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KS4 Chemistry

The Periodic Table

The Periodic Table

Contents

Elements and atomic number

Arranging elements

Electronic structure

Patterns of behaviour

Teacher resources

What are all substances made of?

…to gold, an unreactive metal.

From chlorine, a poisonous gas…

From sodium, a reactive metal…

There are millions of different substances in the world but what are they all made of?

Elements the building blocks of all substances.

There are about 100 different elements in a variety of forms.

…to oxygen, a life-giving gas.

Can you recognise an element by its properties?

You will be given four facts about some everyday substances.

For each one, choose the key fact that shows whether or not it is an element.

1. Is sawdust an element?

Facts about sawdust:a) Sawdust is a poor conductor of electricity.b) You make sawdust by breaking wood into very tiny

pieces.c) When you heat sawdust, it changes to charcoal and

gives off a flammable gas.d) If sawdust is sprinkled on the soil, it slowly rots away.

Choose one key fact.

2. Is oxygen an element?

Facts about oxygen:a) Animal life on Earth depends on oxygen.b) Oxygen is a gas that is very difficult to liquefy.c) Whatever chemical tests you try, oxygen never breaks

down into other substances.d) When oxygen reacts with carbon, it makes carbon

dioxide.


3. Is chalk an element?

Facts about chalk:a) When chalk is heated, it changes into lime and carbon

dioxide.b) When chalk reacts with acids, it forms carbon dioxide.c) Chalk is a common rock; for example, the white cliffs of

Dover are made of chalk.d) Chalk is soft, so it can be used to write with.


4. Is water an element?

Facts about water:a) Water is a liquid at room temperature.b) Fish can live in water by breathing dissolved air.c) When you heat water it boils to make steam; when

steam is cooled it condenses and makes water again.d) When an electric current passes through water, it splits

it up into hydrogen and oxygen.


5. Is salt an element?

Facts about salt:a) Salt enhances the flavour of other foods, making it an

important cookery ingredient.b) Salt is unusual: it is only slightly more soluble in hot

water than in cold water.c) Salt melts at quite a high temperature: 801°C. d) Molten salt changes into sodium and chlorine when an

electric current passes through it.


Can you recognise an element?

In the next section you are not told the names of the substances.

For each one, you have to decide: • Whether it is an element.• Which is the key fact.

You get a bonus mark for each substance you can name correctly.

6. Is Substance 1 an element?Facts about Substance 1:a) It is a brown solid that can be polished to a shiny bright finish.b) When heated, it turns black. At 1085°C it melts to a shiny, runny

liquid.c) The solid and the liquid are very good conductors of electricity.d) When heated, or when it conducts electricity, it does not break

down into other substances.

Is Substance 1 an element?Which is the key fact?What is Substance 1?

7. Is Substance 2 an element?

Facts about Substance 2:a) It is a gas at room temperature.b) It is completely unchanged by heat, electricity or other

chemical substances.c) It glows blue/green when it conducts electricity in a

discharge tube (like a fluorescent light tube).d) About 1% of the Earth’s atmosphere consists of

Substance 2.Is Substance 2 an element?

Which is the key fact?What is Substance 2?

8. Is Substance 3 an element?Facts about Substance 3:a) It is a white, crystalline solid that is non-poisonous and has a

sweet taste.b) When heated it melts, making a thick brown liquid which bubbles

and slowly changes into a black solid.c) Neither the white solid nor the solution conduct electricity.d) It dissolves very well in water.


9. Is Substance 4 an element?

Facts about Substance 4: a) It is a gas at room temperature. b) Below –183°C the gas turns to a liquid. c) The gas is very flammable. d) When it burns, carbon dioxide and water are the only

products.


10. Is Substance 5 an element?Facts about Substance 5: a) It is a solid at room temperature that can exist in several different

forms.b) One form is white, catches fire easily and burns vigorously with a

spluttering yellow flame.c) Another form is reddish brown, catches fire when strongly heated

and burns slowly with a yellow glow.d) Whatever chemical tests you try, none of the forms ever breaks

down into other substances.


Properties of elements

What is a property of an element?

A property is any characteristic of an element.

For example, here are some properties of sodium:

It would be really useful to be able to predict properties of elements instead of having to remember them!

–metallic–highly reactive–solid but melts easily–feels light (low density)

Are there any patterns in the properties of elements?

Properties and atomic number

particleparticle chargecharge relative massrelative mass

proton +1 1

neutron 0 1

electron -1 0.0005

Scientists discovered that the properties of elements seemed to depend on atomic number.

What is the atomic number of an element?

Atoms contain three types of particles:

Where are these particles found in an atom?

What is atomic number?

Atomic number = the number of protons in an atom

proton

electron neutron

heliumnucleus

What are the particles in this helium atom?

What is the atomic number of helium?

Atomic number and electrons

Atoms of elements contain equal numbers of protons and electrons.

Atoms of elements have no charge, they are neutral.

What is the charge on a fluorine atom?

1919

FF99

How are the number of electrons and atomic number related in a neutral atom?

9 protons 9 electrons10 neutrons

charge = +9 charge = - 9 charge = 0

total charge = 0

They are the same.

How does this affect the charge of such atoms?

The Periodic Table

Contents


Arranging elements



Teacher resources

Atomic number and patterns

KH Li NaBe Mg Al PN O S ClF Ne ArSiHe B C

reactive metalsunreactive gases

reactive gases

When scientists arranged elements in order of increasing atomic number they found patterns in their properties.

Positions of similar elements

How many elements are there from one reactive metal to the next?

How many elements are there from one reactive gas to the next?


191 3 114 12 13 157 8 16 179 10 18142 5 6

8

8

Compare the positions of similar elements.

reactive gases reactive metals

Arranging elements

Arranging these strips in rows…

Divide the elements at set intervals, arrange them according to their properties and what patterns do you see?

cut here


191 3 114 12 13 157 8 16 179 10 18142 5 6

cut herecut here

NaMg Al P S Cl ArSi

H He

Li Be N O F NeB C

K

Arranging elements

K

He

Al P SSiMgNa ArCl

Be N OB CLi NeF

When elements are arranged according to their properties what patterns do you see and what element is missing?

reactive metals

unreactive gases

reactive gases

Similar elements go into the same columns.

Hydrogen is an exception. This reactive gas is best positioned above the reactive metals.

Hhydrogen is a special case

The periodic table

Arranging all the elements by atomic number and properties led to the creation of…

the periodic table

H He

Fr Ra Rf Db Sg Bh Hs Mt ? ?Ac ?

K Ca Ga Ge As Se KrSc Ti V Cr Mn Fe Co Ni Cu Zn Br

Cs Ba Tl Pb Bi Po RnHf Ta W Re Os Ir Au HgLa Pt At

Na Mg Al Si P S ArCl

Li Be B C N O NeF

Rb Sr In Sn Sb Te XeY Zr Nb Mo Tc Ru Pd Ag CdRh I

Columns of elements

H

Li

Na

K

Rb

Cs

Fr

Be

Mg

Ca

Sr

Ba

Ra

Ga

In

Tl

Al

B

Ge

Sn

Pb

Si

C

Sb

Bi

P

N

As Se

Te

Po

O

S

He

Kr

Ne

Ar

Rn

Xe

Sc Ti V Cr Mn Fe Co Ni Cu Zn

Y Zr Nb Mo Tc Ru Pd Ag CdRh

Hf Ta W Re Os Ir Au HgLa Pt

Rf Db Sg Bh Hs Mt ? ?Ac ?

Br

At

Cl

F

I

What are columns of elements called?

765432

GroupsGroups

1 0Group number

transition elements

Rows of elements

H He

Li Be N O F NeB C

Na Mg Al P S Cl ArSi

K Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge Se BrCa KrAs

Rb Y Zr Nb Mo Tc Ru Pd Ag Cd In Sn SbSr TeRh I Xe

Cs Ba Hf Ta W Re Os Ir Au Hg Tl Pb Bi PoLa AtPt Rn


PeriodsPeriodsWhat are rows of elements called?

1

2

3

4

5

6

7

Period number

H He

Li

Na

K

Rb

Cs

Fr

Be

Sc Ti

Mg

V Cr Mn Fe Co Ni Cu Zn Ga Ge Se BrCa Kr

Y Zr Nb Mo Tc Ru Pd Ag Cd In Sn SbSr TeRh

Ba Hf Ta W Re Os Ir Au Hg Tl Pb Bi PoLa AtPt

Ra Rf Db Sg Bh Hs Mt ? ?Ac ?

Al P

N O

S Cl

F Ne

Ar

Rn

I

Si

Xe

B C

As

What is the Group and Period of this element?

Mg

C

Group 2 Group 4Group 7

Cl

K

Group 1MgCClK

Name the position

7654321 0

2

3

4

5

6

7

Period 3Period 2Period 3Period 4

1

H1 He

Li

Na

K

Rb

Cs

Fr

Be

Sc Ti

Mg





Al P

N O

S Cl

F Ne

Ar

Rn

I

Si

Xe

B C

As

3

11

19

37

55

87

4

21 22

12

23 24 25 26 27 28 29 30 31 32 34 3520 36

39 40 41 42 43 44 46 47 48 49 50 5138 5245

56 72 73 74 75 76 77 79 80 81 82 83 8457 8578

88 104105106107108109 11111289 110

13 15

7 8

16 17

9 10

18

86

53

14

54

2

5 6

33

Missing elements!

In this periodic table the symbols are replaced by atomic numbers. Some of the numbers are missing – where?

Two more periods of elements fit here but are only shown on some periodic tables. These are called the lanthanides and actinides.

The Periodic Table

Contents


Arranging elements



Teacher resources

Patterns 1: Metals and non-metals

on the left and centre

mostly on the right

Where are different types of elements grouped together on the periodic table?

metals

non-metals

in between metals and non-metalsmetalloids

Metalloids aren’t type of rock music fan!

Metalloids actually have some properties similar to metals and other properties similar to no-metals.

Can you name a metalloid element?

Metals, non-metals and metalloids

H

Li

Na

K

Rb

Cs

Fr

Be

Sc Ti

Mg





Al P

N O

S Cl

F Ne

Ar

Rn

I

Si

Xe

He

B C

As

silicon (Si) metalloidfrancium (Fr) metalscandium (Sc) metalkrypton (Kr) non-metalcobalt (Co) metal

Is this element a metal, non-metal or metalloid?

KrSc

Fr

Si

Co

Metal, non-metal or metalloid?

Only two elements are liquids at room temperature.

Where are elements of different states grouped together on the periodic table?

on the left, in the centre and to the right

only two elements are liquid

solids

liquids

mostly on the far rightgases

mercury bromine

Can you name these two elements?

Patterns 2: Physical state

Physical state

H

Li

Na

K

Rb

Cs

Fr

Be

Sc Ti

Mg





Al P

N O

S Cl

F Ne

Ar

Rn

I

Si

Xe

He

B C

As

krypton (Kr) gas

Kr

niobium (Nb) solid

Nb

barium (Ba)

Ba

solidnitrogen (N)

N

gasbromine (Br)

Br

liquid

Is this element a solid, liquid or gas at room temperature?

Solid, liquid or gas?

Patterns 3: Reactivity of metals

more reactive

mo

re reactive

What happens the reactivity of metals along a period?

H

Li

Na

KRbCs

Fr

Be

Sc Ti

Mg

V Cr MnFe Co Ni Cu ZnGaGeCaY Zr NbMoTc Ru Pd AgCd In Sn SbSr Rh

Ba Hf Ta W ReOs Ir AuHg Tl Pb Bi PoLa Pt

Ra Rf DbSg Bh Hs Mt ? ?Ac ?

Al

What happens the reactivity of metals down a group?

Which is the most reactive metal?

potassium (K) or lithium (Li)

H

Li

Na

KRbCs

Fr

Be

Sc Ti

Mg

V Cr MnFe Co Ni Cu ZnGaGeCaY Zr NbMoTc Ru Pd AgCd In Sn SbSr Rh

Ba Hf Ta W ReOs Ir AuHg Tl Pb Bi PoLa Pt

Ra Rf DbSg Bh Hs Mt ? ?Ac ?

Al

calcium (Ca) or magnesium (Mg)

calcium (Ca) or iron (Fe) copper (Cu) or barium (Ba)

From the positions of these metals in the periodic table, which metal in each pair is the more reactive?

Which metal is more reactive?

Patterns 4: Reactivity of non-metals

more reactive

What are the rules for the reactivity of the non-metals?

1. Group 0 is the most unreactive group of elements.

2. For the remaining non-metals, reactivity increases to the right of a period

Se Br KrTe

At

PN O

S ClF Ne

Ar

Rn I

Si

Xe

HeB C

As

mo

re r

eact

ive

Which is the most reactive non-metal?

unreactive

and up a group.

neon (Ne) or iodine (I)

Which non-metal is more reactive?

Se Br KrTe

At

P

N O

S Cl

F Ne

Ar

Rn I

Si

Xe

HeB C

As

oxygen (O) or silicon (Si) fluorine (F) or chlorine (Cl)

carbon (C) or oxygen (O)

From the positions of these non-metals in the periodic table, which non-metal in the pair is the more reactive?

The Periodic Table

Contents


Arranging elements



Teacher resources

Patterns and atomic number

What links atomic number and the properties of elements?

The periodic table shows that patterns in the properties of elements are linked to atomic number.

electrons H He


K Ca Ga Ge As Se KrSc Ti V Cr Mn Fe Co Ni Cu Zn Br

Cs Ba Tl Pb Bi Po RnHf Ta W Re Os Ir Au HgLa Pt At

Na Mg Al Si P S ArCl

Li Be B C N O NeF

Rb Sr In Sn Sb Te XeY Zr Nb Mo Tc Ru Pd Ag CdRh I

ATOMS All atoms of the same element have the

same proton number.

1H

2He

3Li

5B

4Be 6C

7 N

9F10Ne

11Na12Mg

16S

17Cl

18Ar

19K

20Ca8O

13Al

14Si15P

Elements 1–20

Number of electrons = number of protons (unless the atom is charged).

The size of the nucleus compared with the size of the atom is like ‘the size

of a man’s fist compared with the dome of St Paul’s Cathedral’ (Rutherford).

INSIDE AN ATOM

The nucleus contains almost the entire mass of the atom.

Tiny electrons whizz around the nucleus.

Almost all of the atom is empty space.

ELECTRONSElectrons can’t just go

anywhere. They move in spaces called orbitals.

nucleuselectron

Diagram not to scale.

Orbitals have complicated shapes

which are represented by the circles.

The further away they are from the nucleus, the higher the energy

of the electrons.

ENERGY LEVELS ON A HILLSIDE

Part of a hill

These stones have least energy because they are

nearest the bottom.

This stone has most energy because it has furthest to fall.

Each different height from the ground is an ENERGY LEVEL. Stones must be at one level or

another, not in between.

Increasing energy

Increasing energy

Level 1

Level 2

Level 3

Level 4

2

Nucleus

8

18

32

The further away you move from the nucleus, the more orbitals available, but they are of higher energy.

ENERGY LEVELS AROUND THE NUCLEUS OF AN ATOM

Figures in red show maximum number of electrons in each energy level.

Energy

Level 1

Level 2

Level 3

Level 4

2

Nucleus

8

18

32

ARRANGEMENT OF ELECTRONS IN A HYDROGEN ATOM: 1H

Electronic configuration: 1.

The electron occupies the lowest available

energy level.

Energy

Level 1

Level 2

Level 3

Level 4

2

Nucleus

8

18

32

ARRANGEMENT OF ELECTRONS IN A HELIUM ATOM: 2He

Electronic configuration: 2.

The electron occupies the lowest available

energy level.

Energy

Level 1

Level 2

Level 3

Level 4

2

Nucleus

8

18

32

ARRANGEMENT OF ELECTRONS IN A LITHIUM ATOM: 3Li

Electronic configuration: 2, 1.

The new electron occupies the lowest

available energy level.

filled orbital

most recently filled orbital

Energy

Level 1

Level 2

Level 3

Level 4

2

Nucleus

8

18

32

ARRANGEMENT OF ELECTRONS IN A NEON ATOM: 10Ne

Electronic configuration: 2, 8.



filled orbital


Energy

Level 1

Level 2

Level 3

Level 4

2

Nucleus

8

18

32

ARRANGEMENT OF ELECTRONS IN A POTASSIUM ATOM: 19K

Electronic configuration: 2, 8, 8, 1.



filled orbital


not available

Energy

Level 1

Level 2

Level 3

Level 4

2

Nucleus

8

18

32

ARRANGEMENT OF ELECTRONS IN A CALCIUM ATOM: 20Ca




filled orbital


not available

Energy

Level 1

Level 2

Level 3

Level 4

2

Nucleus

8

18

32

ARRANGEMENT OF ELECTRONS IN A SCANDIUM ATOM: 21Sc




filled orbital


ELECTRON ARRANGEMENTS AND THE PERIODIC TABLE

This periodic table shows all the elements in proton number order. The number of elements in each period is shown in red.

2

8

8

18

18

32

30

FAMILIES OF METALS

Group 1

3Li 2, 1

11Na 2, 8, 1

19K 2, 8, 8, 1

37Rb 2, 8, 18, 8, 1

55Cs 2, 8, 18, 18, 8, 1

Group 2

4Be 2, 2

12Mg 2, 8, 2

20Ca 2, 8, 8, 2

38Sr 2, 8, 18, 8, 2

56Ba 2, 8, 18, 18, 8, 2

Increasing reactivity


FAMILIES OF NON-METALS

Group 6

8O 2, 6

16S 2, 8, 6

Group 7

9F 2, 7

17Cl 2, 8, 7

35Br 2, 8, 18, 7

53I 2, 8, 18, 18, 7



THE NOBLE GASES

Group 0

2He 2

10Ne 2, 8

18Ar 2, 8, 8

36Kr 2, 8, 18, 8

54Xe 2, 8, 18, 18, 8Almost completely

unreactive

FORMING A SODIUM ION

Sodium atom, Na, 2, 8, 1. Sodium ion, Na+, 2, 8.

Na(g) Na+(g) + e–

The sodium ion is much smaller than the sodium atom.

Energy

Level 1

Level 2

Level 3

Level 4

Nucleus

FORMING POSITIVE IONS

The more energy the electron already has, the less extra energy is needed to remove it.

Complete orbitals shield the outer electrons from the pull of the nucleus.

This means it takes less energy to remove an electron from an outer orbital than from an inner one.

Li Li+ + e– requires 520 kJ/mol.

Cs Cs+ + e– requires 376 kJ/mol.

Given enough extra energy, an electron can escape from the pull

of the nucleus.

The higher its energy level, the less extra energy it will

need.

Na Na+ + e– requires 496 kJ/mol.

Estimate the values for K and Rb.

FORMING A CHLORIDE ION

Cl(g) + e– Cl–(g)

The chloride ion is largerthan the chlorine atom.

Chlorine atom, Cl, 2, 8, 7. Chloride ion, Cl–, 2, 8, 8.

Energy

Level 1

Level 2

Level 3

Level 4

Nucleus

FORMING NEGATIVE IONS

The stronger the attraction of the nucleus for an extra electron, the more energy will be given out when a negative ion is formed.

Complete orbitals shield the outer electrons from the pull of the nucleus. So the larger the atom, the less its attraction for an extra electron.

Cl + e– Cl– gives out 349 kJ/mol. Estimate the value

for iodine.

The nucleus can attract

electrons into the outer shell of the atom.

The smaller the atom, the

stronger the pull of the nucleus.

Br + e– Br –

gives out 325 kJ/mol.

Patterns of electron arrangements

2,8,8,1 2,8,8,2

2,8,1 2,8,2

1

2,1 2,2

Consider the electron arrangements of the first 20 elements in the periodic table.

7654321 0

1

2,3 2,4 2,5 2,6 2,7 2,8

2,8,3 2,8,4 2,8,5 2,8,6 2,8,7 2,8,8

2

2

3

4

What is the pattern for the number of outer shell electrons in each group?

Why do elements in the same group have similar chemical reactivity?

Why does reactivity increase going down the group?

Going down Group 1 the outer electron becomes further from the nucleus and so is more easily lost in chemical reactions.

The Group 1 metals are called the alkali metals.

1

2

3

2,1

Li

2,8,1

Na

Group 1 elements have one electron in the outermost shell.

Electrons in Group 1

Group 2 elements have two electrons in the outermost shell.

2,2

Be

2,8,2

Mg

2

2

3

In chemical reactions metals tend to lose their outer electrons to form positive ions.

What is the charge on the ions of Group 2 elements?

These elements lose the two outer electrons and form ions with a 2+ charge.


Group 3 elements have three electrons in the outermost shell.

3

2

3

2,3

B

2,8,3

Al

Metals lose their outer electrons to form positive ions.

What is the charge on the ions of Group 3 elements?

These elements lose the three outer electrons and form ions with a 3+ charge.


Group 4 elements have four electrons in the outermost shell.

4

2

3

2,4

C

2,8,4

Si

The elements at the top of Group 4 are non-metals.

These elements don’t like to lose their electrons and prefer to share them with other atoms.

What type of bonding is this?

The elements at the top of Group 4 bond covalently.


Group 5 elements have five electrons in the outermost shell.

5

2

3

2,5

N

2,8,5

P

How many electrons do the elements shown need for a full outer shell?

The Group 5 elements shown need three more electrons to achieve a full outer shell.


Atoms form negative ions by gaining extra electrons. What type of ions will these Group 6 elements form?

These Group 6 atoms can gain two extra electrons to complete their outer shell and form negative ions with a 2- charge.

6

2

3

2,6

O

2,8,6

S

Group 6 elements have six electrons in the outermost shell.


Group 7 elements have seven electrons in the outermost shell.

7

2

3

2,7

F

2,8,7

Cl

These atoms need one extra electrons for a complete outer shell and form 1- ions.

Why does reactivity increase going up Group 7?

The incoming electrons are pulled more strongly into shells that are closer to the nucleus.


Group 0 (or 8) elements all have a complete set of electrons in the outermost shell.1

2

3

0

2

He

2,8

Ne

2,8,8

Ar

Why are these elements so unreactive?

The Group 0 atoms do not need to lose or gain any electrons to complete their outer shells which means they are unreactive.

The Group 0 elements are called the noble (or inert) gases.


H He

Li

Na

K

Rb

Cs

Fr

Be

Sc Ti

Mg





Al P

N O

S Cl

F Ne

Ar

Rn

I

Si

Xe

B C

As

Mg

C

2, 8, 22, 42, 8, 7

Cl

K

2, 8, 8, 1MgCClK

What is the electron arrangement?

What is the electron arrangement in this element’s atoms?

7654321 0

2

3

4

5

6

7

1

Different types of elements

Periodic table quiz

The Periodic Table

Contents


Arranging elements



Teacher resources

H

Li

Na

K

Rb

Cs

Fr

Be

Sc Ti

Mg





Al P

N O

S Cl

F Ne

Ar

Rn

I

Si

Xe

He

B C

As

Periodic table

THE ALKALI METALS

Alkali metals and the Periodic Table

These are the alkali metals or Group 1 Elements.

H

Li

Na

K

Rb

Cs

Fr

Be

Sc Ti

Mg





Al P

N O

S Cl

F Ne

Ar

Rn

I

Si

Xe

He

B C

As

Li

Na

K

Rb

Cs

Fr

Electronic Structure

• All the Group 1 elements have 1 electron in the outermost shell.

Li

Na

K

Rb

Cs

Lithium

Sodium

Potassium

Rubidium

Caesium

2,8,1

2,8,8,1

2,1

Trends in Density

Lithium, sodium and potassium are all less dense than water and so will float.Densities follow a general, although not perfect, trend.

Element Symbol Density

Lithium Li 0.53

Sodium Na 0.97

Potassium K 0.86

Rubidium Rb 1.53

Caesium Cs 1.88

Melting Points

The atoms in the Group 1 elements are bonded together using just one outer shell electron per atom.

As a result, melting points are low compared to most metals.

Element Melt. Point (C)

Lithium 181

Sodium 98

Potassium

Rubidium 39

Caesium

Can you predict the missing data?

63

29

Trends in Chemical Reactivity

Reactivity increases down the group.

Reactions all involve the loss of the outermost electron which changes the metal atom into a metal 1+ ion.Losing this electron seems to get easier as we go down the group.

Li

Na

K

Rb

Cs

Rea

ctiv

ity I

ncre

ases

Reactivity and Electron Structures

1. The outer electron (-) gets further from the nucleus (+) as you go down the group. This reduces the force of attraction.

2. The inner shells ‘shield’ the outermost electron from the attraction from the nucleus.

Both factors make it easier to lose the outer electron as you go down the group.

Rea

ctiv

ity

Incr

ease

s

Reaction with Water

The Group 1 elements all react vigorously with water.

Hydrogen gas is produced which sometimes catches fire.

An alkali is left behind in the solution which is why these elements are often called ‘The Alkali Metals’.

Reaction of Lithium

H HO

H HO

HH

Li+

+Li

HO-

HO-

LiLi

Reaction of Lithium with Water

Lithium fizzes quickly in water forming lithium hydroxide and hydrogen.

Lithium + water Lithium hydroxide + hydrogen

2Li(s) + 2H2O(l) 2LiOH(aq) + H2(g)

The solution that remains is strongly alkaline.

Reaction of Sodium with Water

Sodium fizzes very quickly in water. The gas given off can be ignited by a lighted splint.

Sodium + water Sodium hydroxide + hydrogen

2Na(s) + 2H2O(l) 2NaOH(aq) + H2(g)

sodium on water enlarged

Potassium with Water

• Lithium fizzes. Sodium reacts more vigorously. • What will potassium do?

Potassium + water

2K(s) + 2H2O(l)

Potassium hydroxide + hydrogen

2KOH(aq) + H2(g)

What will the word equation and chemical equations be for the reaction of potassium with water?

Potassium + water

The Group 1 Metals and oxygen

The Group 1 elements burn in air to form metal oxides. Don’t try to put them out with water!

Lithium + oxygen Lithium Oxide

4Li (s) + O2(g) 2 Li2O (s)

What will the word equation and chemical equations be for the reaction of sodium with air?

Sodium + oxygen

Na(s) + O2 (g)

sodium oxide

2Na2O (s)4

The Group 1 Metals and chlorine

The Group 1 elements burn in chlorine to form metal chlorides.

Lithium + chlorine Lithium chloride

2Li (s) + Cl2(g) 2 LiCl (s)

What will the word equation and chemical equations be for the reaction of sodium with chlorine?

Sodium + chlorine

Na(s) + Cl2 (g)

Sodium chloride

2NaCl (s)2

Uses of the Group 1 Metals

The metals themselves are too reactive to have many uses although sodium vapour gives street lights their yellow glow.

Lithium metal is used to improve the strength of aircraft alloys and is also used in some electrical batteries.

Common sodium compounds include “salt”, (sodium chloride), “bicarbonate” (sodium hydrogen carbonate), washing soda (sodium carbonate) and caustic soda (sodium hydroxide.)Potassium compounds are used in “NPK fertilisers”, in weedkillers, explosives and many other chemicals.

sodium light

potassium

Using sodium to transfer heat

It needs to include:

The benefits of using sodium to transfer heat and the fact that risks resulting from chemical reactivity are containable.

The chemical reactivity of sodium and the fact that if containment did fail the whole power station could blow up.

Whether there are other safer metals that could be used in place of sodium.

The activity

Following an accident at a nuclear power station three groups are represented at a public meeting.

The debate centres around an accident involving a spill of molten sodium metal which was being used to cool the reactor.

The Incident

• Most power stations burn a fossil fuel and use water to transfer heat from the burners to the turbine area.

• An alternative to water is sodium. Although solid it melts fairly easily and is a better conductor of heat than water.

• This has prompted its use as a coolant to absorb and transfer the heat produced in nuclear power stations.

• To Japan, a country with no fossil fuels, nuclear power is particularly attractive. However, in 1996 Japan’s nuclear industry suffered a setback when a split in a stainless steel pipe spewed 3 tonnes of molten sodium over the reactor floor.

• Nuclear representatives say there was no radiation leak and opponents to nuclear power were whipping up public concern.

• Anti-nuclear protestors say that had it leaked underneath the floor the entire nuclear station would have been at risk.

• The government agreed to make plans about how to deal with a nuclear accident just in case one did ever happen.

Nuclear Industry Representatives groupNuclear Industry Representatives group

• Make a case as to why Japan must have nuclear power.

• Spell out the very low accident rate in the industry.• Explain why a liquid that can absorb heat better is a

good thing (safer?) for a nuclear reactor.• Spell out the fact that you understand the common

reactions of sodium and had already set in place systems to prevent these reactions being a danger.

• Make clear that there is no totally safe way of generating energy and that use of fossil fuels also entails accidents and guaranteed pollution.

Anti-Nuclear Protest groupAnti-Nuclear Protest group

• Explain that risk assessment must take account both of the chances of an accident and the impact of that accident. Leaked long lasting radioactive material or even melt-down and nuclear explosion!

• Challenge the use of sodium (rather than larger volumes of water) as representing a needless risk.

• Spell out in detail the possibility of explosive reactions involving sodium and potentially devastating outcomes.

• Other fuels are available even if they have to be imported.

Dr Ivan Idea SyndicateDr Ivan Idea Syndicate

• One of the main reasons for using sodium is that it melts easily and, as a metal, it conducts heat well.

• Check out the melting point, reactivity and toxicity of other metals and consider the feasibility of using them.

• Are there particular risks you would need to guard against? Can you suggest ways to minimise these?

• Or - should you just go back to using water for heat transfer?

Dr Ivan Idea Syndicate 2Dr Ivan Idea Syndicate 2Some data on the metals that melt below 500oC.

Metal Symbol At Mass Melt Point (oC ) Relative costMercury Hg 200.59 -38.7 10Caesium Cs 132.9 28.6 25Gallium Ga 69.72 29.9 1055Francium Fr 223 30 unavailableRubidium Rb 85.47 39 198Potassium K 39.1 63.8 7.4Sodium Na 22.99 98 1Indium In 114.82 156.8 unavailableLithium Li 6.94 179 26

How many electrons do the alkalimetals have in their outer shell?

A. 1B. 2C. 4D. 7

What charge ions are formed by thealkali metals?

A. 4B. 3C. 2D. 1

Which answer places the alkali metals in order of increasing reactivity?

A. Na, Li, K,B. K, Na, LiC. Li, Na, KD. Li, K, Na

When alkali metals react with waterwe get:

A. Hydrogen + a metal oxideB. Oxygen + a metal oxide C. Hydrogen + a metal hydroxideD. Oxygen +a metal hydroxide

What will the melting point of caesium be?

A. -10oC B. 0oC C. 25oC D. 38oC

181

98

63

3929

0

50

100

150

200

0 2 4 6 8

Period

M.P

t (C

)

Li

Na

KRb Cs Fr

Meet the halogens

The elements in Group 7

Discovery

Element Symbol Discovered by Date

chlorine Cl Carl Wilhelm Scheele 1774

iodine I Bernard Courtois 1811

bromine Br Antoine Ballard 1826

fluorine F Joseph Henri Moissan 1886

astatine At Dale Corson 1940

Physical propertiesElement Appearance Electrical

conductivitym.p. (°C)

b.p.(°C)

fluorine F pale yellow gas poor –220 –188

chlorine Cl dense green gas poor –101 –35

bromine Br volatile brown liquid, orange vapour

poor –7 58.8

iodine I shiny dark grey solid, violet vapour

poor 114 184

astatine At

Atomic properties

2, 8, 18, 18, 725412753I2Iiodine

2, 8, 18, 71608035Br2Brbromine

2, 8, 77135.517Cl2Clchlorine

2, 738199F2Ffluorine

Electron arrangement

Molecular weight

Atomic weight

Atomic number

FormulaSymbolElement

Name the halogen (1)

• This halogen is used to make dyes and medicines.

• The vapour is poisonous and has a choking smell.

• One of only two elements that are liquids at room temperature.

• Changes to a brown vapour on warming.


• Made by passing electricity through salt water.

• Poisonous: used as a weapon in the First World War (1914–1918).

• A powerful bleach when moisture is present.

• A green gas at room temperature.


• This halogen can be obtained from seaweed.• Turns bright blue if starch is present in even a

tiny amount.• Dissolves in alcohol and was formerly used as a

disinfectant.• A black solid that changes to a purple vapour on

warming.

Which is the chlorine?

A Green gas

B Colourless gas

C Brown gas

Which is the iodine?

Appearance Effect of heat in a test tube

A Black powder Glows red-hot but otherwise unchanged.

B Black powder Changes into a violet vapour without melting. Vapour turns back to solid on cooling.

C Black powder Glows red-hot and gradually disappears.

Which is the bromine?

Melting point

Boiling point

A 7C 59C

B 113C 445C

C –112C –108C

Which is the fluorine? The coloured circles represent atoms of different elements.

A B C

THE TRANSITIONMETALS

The Transition elements

Transition means “an in betweenin between state” and the transition elements come in between Group 2 and Group 3.


Y Zr Nb Mo Tc Ru Pd Ag CdRh

Hf Ta W Re Os Ir Au HgLa Pt

Rf Db Sg Bh Hs Mt ? ?Ac ?

H

Li

Na

K

Rb

Cs

Fr

Be

Mg

Ga Ge Se BrCa Kr

In Sn SbSr Te

Ba Tl Pb Bi Po At

Ra

Al P

N O

S Cl

F Ne

Ar

Rn

I

Si

Xe

He

B C

As

Gp 2 Gp 3

Transition Elements

General Characteristics

They are less reactivethan Group 1 orGroup 2 metals.

They mostly formcoloured

compounds.

They havehigh melting

points.

They have high density.

Transition metalsare often referred toas ‘typical’ metals.

TransitionElements

They often act as

catalysts.

Properties – density

• Similarities are more noticeable than differences although there are still some broad patterns.

• They are all dense which is what we expect of metals.

0

1

2

3

4

5

6

7

8

9

Density (g/cm-3)

Sc

Ti

V

Cr

Mn

Fe

Co

Ni

Cu

Zn


Properties – melting point

Melting points show no regular pattern – other than nearly all being high which is typical of metals.(Note zinc doesn’t fit very well on either density or melting point.)

0200400600800

100012001400160018002000

Melting Point ( C)

Sc

Ti

V

Cr

Mn

Fe

Co

Ni

Cu

Zn


Properties – reactivity

• Again it is similarities that stand out rather than differences: they tend to react relatively slowly (e.g.) with air, water and acid.

• The general trend is to reduced activity across the Periodic Table but again the trend is far from perfect with zinc in particular being more reactive than you might expect.


General reduced reactivity

Rusting: a slow

but costly

process!

Properties – catalysis

• A catalyst is a substance that speeds up a chemical reaction without being used up.

• Catalysts are hugely valuable in industry where they can save time and energy.

• Many transition elements ( and their compounds) are catalysts.

VTi

Used in plastic manufacture

Fe

Ni

Used in oil hydrogenation

Uses

The three most commonly known transition elements are iron or steel, copper and zinc.

iron or steel

General engineering

metal

copper

Electrical and

plumbing work

zinc

Galvanising steel to

protect it

Pair the metal up with its uses

iron or steel

copper

zinc

Pair the metal catalyst with the substance.

V

Ti

Fe

Ni

Pair the statement about the transition elements with the words.

The **** elements fit between group 2 and 3.

catalysts

They tend to be very**** reactive

Most are not especially *** coloured

They are all typical**** similar

They often form compounds that are ****

transition

They often speed up reactions by acting as ****

metals

Which is a true statement about most

transition elements?

A. They are non-metals.

B. They are light (low density).

C. They are strong.

D. They are non-conductors.

Which of these does copper NOTNOT tend to be

used for?

A. Plumbing work.

B. Electrical work

C. Ornaments and jewellery

D. Tools

Transition elements can speed up other reactions without getting used up in the process. What do we call substances that do this?

A. CapitalistsB. CatalystsC. CatholicsD. Catapults

Transition elements often form coloured compounds. What colour compound does copper usually form?

A.Blue B.Yellow C.RedD.Violet

How would you describe the reactivity of transition elements within the Periodic Table?

A.Always more reactive across periods (left to right).B.Generally less reactive across periods (left to right).C.No change in reactivity. D.Changes but no trends in reactivity.

AcidityIntroducing key ideas

about acidity

Tests for acidity

Reactions of dilute sulfuric acid (10% H2SO

4)

Test Examples ResultsIndicators • methyl orange

• phenolphthalein• universal indicator

Metals • magnesium

Carbonates • sodium carbonate

Oxides • copper oxide

Alkalis • sodium hydroxide solution

Electrical conductivity

• carbon electrodes connected to a lamp and power supply

Tests for acidity

Reactions of concentrated sulfuric acid (98% H2SO

4)

Test Examples ResultsIndicator universal indicator paper (DRY)

Metals magnesium (DRY)

Carbonates sodium carbonate (DRY)

Oxides copper oxide (DRY)


DRY carbon electrodes connected to a lamp and power supply

Diluting sulfuric acid

Water reacts with sulfuric acid, forming H+ ions.H+ ions give acids their acidic properties.

Acids need water before they can react like acids.

water

2–H2SO

4(l)

2H+(aq) + SO

4 (aq)

Always add acid to water, not water to acid.

What is an H+ ion?

hydrogen atom

1 proton + 1 electron

hydrogen ion

1 proton

In water, the proton is attached to a water molecule to make the H+(aq) ion.

Hydrogen chloride, HCl

Test Solution in toluene Solution in waterIndicator paper

Magnesium ribbon

Sodium carbonate

Copper oxide

Sodium hydroxide solution


Hydrogen chloride + water

HCl(g) H+(aq) + Cl– (aq)

Water reacts with hydrogen chloride, forming H+(aq) ions.

H+(aq) ions gives hydrochloric acid its acidic properties.

One mole of HCl gas produces one mole of H+(aq) ions.

water

hydrochloric acid

Strong acids

HX H+(aq) + water

SO4 (aq)+2H+(aq)H2SO4

NO3(aq)+H+(aq)HNO3

Cl–(aq)+H+(aq)HCl

–

2–

X–(aq)

Weak acids

Weak acids partially ionise in water.

One mole of acid gives less than one mole of H+(aq) ions.

CH3CO2(aq)+H+(aq)CH3CO2H

X–(aq)+H+(aq)HXWater

–

Representing Chemicals

Symbols and formulae

Chemical Symbols of elements

• Each element has a symbol. • Many you can predict from the name of the

element.

• And some you can’t!

Atom

PPPhosphorus

NNNitrogen

OOOxygen

HHHydrogen

SymbolName

O

N

H

P

AgAgSilver

PbPbLead

CuCuCopper

NaNaSodium

SymbolAtomName

Na

Cu

Ag

Pb

Chemical formula of elements• Each element has a symbol.

• Some elements exist as particular numbers of atoms bonded together.

• This fact can be represented in a formula with a number which shows how many atoms.

O

N

H H H

P

N N

FormulaMoleculeAtom

O O

P PP

P

O2

N2

H2

P4

The formula of molecular compounds

Water

Carbon dioxide

MethaneFormulaName

C H

H

H

H

CO O

H

HO

• Molecular compounds have formulae that show the type and number of atoms that they are made up from.

CH4

CO2

H2O

The formula of ionic compounds• Ionic compounds are giant

structures.• There can be any number of

ions in an ionic crystal - butbut always a definite ratio of ions.

Name Ratio Formula

Sodium chloride 1:1

Magnesium chloride 1:2

Aluminium chloride 1:3

Aluminium Oxide 2:3

+ -+-

+

--+ +

+-+

-

- --+

++ -

+-+

--+ +

Sodium chloride

A 1:1 ratio

NaCl

AlCl3

Al2O3

MgCl2

Ions with groups of atoms

• Some ions are single atoms with a charge.

• Other ions consist of groups of atoms that remain intact throughout most chemical reactions.

• E.g. Nitrate and sulphate ions commonly occur in many chemical reactions.

Chloride ClCl--

nitride NN3-3-

Sulphide SS2-2-

Cl-

N3-

S2-

nitrate

NONO33--

Sulphate

SOSO442-2-

NO O-

O

S

O

O-O-

O

Use of brackets in formulae• Ions like nitrate and sulphate remain unchanged

throughout many reactions. • Because of this we tend to think of the sulphate ion as a

“group” rather than a “collection of individual” sulphur and oxygen atoms.

• This affects how we write formulae containing them. Aluminium sulphate contains two Al ions and three sulphate ions.

• We write it as AlAl22(SO(SO44))3 3

Not AlAl22SS33OO1212

• Similar rules apply to ions such as nitrate NO3-,

hydroxide OH-, etc.

Use the information to write out the formula for the compound.

1) Calcium bromide (One calcium ion, two bromide ions)

2) Ethane(Two carbon atoms, six hydrogen atoms)

3) Sodium oxide(Two sodium ions, one oxygen ion)

4) Magnesium hydroxide(One magnesium ion, two hydroxide ions)

5) Calcium nitrate(One calcium ion, two nitrate ions)

CaBr2

C2H6

Na2O

Mg(OH)2

Ca(NO3)2

Activity

The Masses of chemicals

Atomic Mass of elements• The atoms of each element have a different mass.• Carbon is given a relative atomic mass (RAM) of 12Carbon is given a relative atomic mass (RAM) of 12..• The RAM of other atoms compares them with carbon.• Eg. Hydrogen has a mass of only one twelfth that of carbon

and so has a RAM of 1.• Below are the RAMs of some other elements.

Element Symbol Times as heavy as carbon R.A.M

Helium He one third

Beryllium Be three quarters

Molybdenum Mo Eight

Krypton Kr Seven

Oxygen O One and one third

Silver Ag Nine

Calcium Ca Three and one third

4

12

96

84

16

108

40

Formula Mass• For a number of reasons it is useful to use

something called the formula mass.• To calculate this we simply add together the

atomic masses of all the atoms shown in the formula. (N=14; H=1; Na=23; O=16; Mg=24; Ca=40)

Substance Formula Formula Mass

Ammonia NHNH33

Sodium oxide NaNa22OO

Magnesium hydroxide Mg(OH)Mg(OH)22

Calcium nitrate Ca(NOCa(NO33))22

14 + (3x1)=17

(2x23) + 16 =62

24+ 2(16+1)=58

40+ 2(14+(3x16))=164

Percentage Composition• It is sometimes useful to know how much of a compound

is made up of some particular element. • This is called the percentage composition by mass.

% Z = (Number of atoms of Z) x (atomic Mass of Z)Formula Mass of the compound

0

20

40

60

80

%

Carbon OxygenE.g. % of oxygen in carbon dioxide (Atomic Masses: C=12. O=16)

Formula = Number oxygen atoms

= Atomic Mass of O = 16 Formula Mass CO2 =

% oxygen =

CO2

2

12 +(2x16)=442 x 16 / 44 = 72.7%

Formula Atoms of O

Mass of O

Formula Mass

%age Oxygen

MgO 1

K2O 1

NaOH 1

SO2 2

• Calculate the percentage of oxygen in the compounds shown below

32+(2x16)=64

32

23+16+1=4016

(2x39)+16 =94

16

24+16=4016 16x100/40=40%

16x100/94=17%

16x100/40=40%

32x100/64=50%

% Z = (Number of atoms of Z) x (atomic Mass of Z)Formula Mass of the compound

Activity

• Nitrogen is a vital ingredient of fertiliser that is needed for healthy leaf growth.

• But which of the two fertilisers ammonium nitrate or urea contains most nitrogen?

• To answer this we need to calculate what percentage of nitrogen is in each compound

Activity

Formula Atoms of N

Mass of N

Formula Mass %age Nitrogen

NH4NO3 2 28

CON2H4 2 28

• Formulae: Ammonium Nitrate NH4NO3: Urea CON2H4

28x100 /80 = 35%

28x100 /60 = 46.7%

14+(1x4)+14+(3x16)=80

12+16+(2x14+(4x1)=

60

And so, in terms of % nitrogen urea is a better fertiliser than ammonium nitrate

0

10

20

30

40

50

1st Qtr

Amm.Nitrate UreaAtomic masses H=1: C=12: N=14: O=16

Activity

Formula from Composition by mass.

Formula Mass• When a new compound is discovered we have to

deduce its formula.• This always involves getting data about the

masses of elements that are combined together.• What we have to do is work back from this data to

calculate the number of atoms of each element and then calculate the ratio.

• In order to do this we divide the mass of each atom by its atomic mass.

• The calculation is best done in 5 stages:

• We found 3.2g of copper reacted with 0.8g of oxygen. What is the formula of the oxide of copper that was formed? (At. Mass Cu=64: O=16)

SubstanceSubstance Copper oxideCopper oxide

1. Elements CuCu OO

2. Mass of each element (g)

3. Mass / Atomic Mass

4. Ratio

5. Formula

3.23.2 0.80.8

3.2/64 =0.053.2/64 =0.05 0.8/16 =0.050.8/16 =0.05

1:11:1

CuOCuO

• We found 5.5g of manganese reacted with 3.2g of oxygen. What is the formula of the oxide of manganese formed? (Atomic. Mass Mn=55: O=16)

SubstanceSubstance Manganese oxideManganese oxide

1. Elements MnMn OO

2. Mass of each element (g)


4. Ratio

5. Formula

5.55.5 3.23.2

5.5/55 =0.105.5/55 =0.10 3.2/16 =0.203.2/16 =0.20

1:21:2

MnOMnO22

• A chloride of silicon was found to have the following % composition by mass: Silicon 16.5%: Chlorine 83.5%

(Atomic. Mass Si=28: Cl=35.5)

SubstanceSubstance Silicon ChlorideSilicon Chloride

1. Elements SiSi Cl

2. Mass of each element (g per 100g)


4. Ratio

5. Formula

16.516.5 83.583.5

16.5/28 =0.5916.5/28 =0.59 83.5/35.5 =2.3583.5/35.5 =2.35

ClCl÷Si = (2.35 ÷ 0.59) = (3.98) ÷Si = (2.35 ÷ 0.59) = (3.98)

Ratio of Ratio of ClCl:Si =4:1:Si =4:1

SiSiClCl44

Divide biggest by smallest

Activity

• Calculate the formula of the compounds formed when the following masses of elements react completely:

(Atomic. Mass Si=28: Cl=35.5)

Element 1Element 1 Element 2Element 2 Atomic MassesAtomic Masses FormulaFormula

Fe = 5.6g Cl=106.5g Fe=56 Cl=35.5

K = 0.78g Br=1.6g K=39: Br=80

P=1.55g Cl=8.8g P=31: Cl=35.5

C=0.6g H=0.2g C=12: H=1

Mg=4.8g O=3.2g Mg=24: O=16

FeClFeCl33

KBrKBr

PClPCl55

CHCH44

MgOMgO

Activity

Formula from Charges on ions

Charges on ions.• Many elements form ions with some definite

charge (E.g. Na+, Mg2+ and O2-). It is often possible to work out the charge using the Periodic Table.

• If we know the charges on the ions that make up the compound then we can work out its formula.

• This topic is covered in more detail in the Topic on Bonding but a few slides are included here on how to work out the charges on ions and use these to deduce the formula of simple ionic compounds.

Charges and Metal ions• Metals usually lose electrons to empty this outer shell. • The number of electrons in the outer shell is usually The number of electrons in the outer shell is usually

equal to the group number in the Periodic Table. equal to the group number in the Periodic Table. • Eg. Li =Group 1 Mg=Group2 Al=Group3

Mg

2.8.2 Mg2+

Al

2.8.3 Al3+

Li

2.1Li+

Charges and non-metal ions• Elements in Groups 4 onwards generally gain electrons

and the number of electrons they gain is equal to the Group Number.

• Oxygen (Group 6) gains (8-6) =2 electrons to form O2-

• Chlorine (Group 7) gains (8-7)=1 electron to form Cl-

ClO

2.62.8 O

O2-

2.8.7 2.8.8 Cl Cl-

• Copy out and fill in the Table below showing what charge ions will be formed from the elements listed.

H He

Li

Na

K

Be

Sc Ti

Mg


Al P

N O

S Cl

F Ne

ArSi

B C

As

Mg

C

Cl

K

Symbol Li N Cl Ca K Al O Br NaGroup No

Charge

1 5 7 2 1 3 6 7 1

1+ 3- 1- 2+ 1+ 3+ 2- 1- 1+

1 2 3 4 5 6 7 0

Activity

The formulae of ionic compounds

This is most quickly done in 5 stages.Remember the total + and – charges must =zeroRemember the total + and – charges must =zero• Eg. The formula of calcium bromide.

1. Symbols: Ca Br

2. Charge on ions 2+ 1-3. Need more of Br4. Ratio of ions 1 25. Formula CaBrCaBr22

BrCa

Br

Ca2+

Br-

Br-

2 electrons

• Eg. The formula of aluminium bromide.

1. Symbols: Al Br

2. Charge on ions 3+ 1-3. Need more of Br4. Ratio of ions 1 35. Formula AlBrAlBr33

BrAl

Br

Br

3 electrons

Al3+ Br-

Br-

Br-


• Eg. The formula of aluminium oxide.

1. Symbols: Al O2. Charge on ions 3+ 2-3. Need more of O4. Ratio of ions 2 3 (to give 6 e-)5. Formula AlAl22OO33

OAl

O

OAl

2e-

2e-

2e-

Al3+

O2-

O2-

O2-

Al3+


• Eg. The formula of magnesium chloride.

1. Symbols: Mg Cl2. Charge on ions3. Need more of4. Ratio of ions5. Formula

2+ 1-

Cl1:2

MgCl2

Cl

MgCl

1e-

1e-

Cl-

Mg2+

Cl-

The formulae of ionic compoundsActivity

• Eg. The formula of sodium oxide.

1. Symbols: Na O2. Charge on ions3. Need more of4. Ratio of ions5. Formula

ONa

Na 1e-

1e- Na+

O2-

Na+

1+ 2+Na

2 : 1Na2O

ActivityThe formulae of ionic compounds

• Using the method shown on the last few slides, work out the formula of allall the ionic compounds that you can make from combinations of the metals and non-metals shown below:

•Metals: Li Ca Na Mg Al K

•Non-Metals: F O N Br S Cl

Activity

Representing Chemical reactions:Equations.

Word Equations• All equations take the general form:

Reactants ProductsWord equations simply replace “reactants andproducts” with the names of the actual reactants and products. E.g

ReactantsReactants ProductsProducts

Magnesium + oxygenMagnesium + oxygen

Sodium + waterSodium + water

Magnesium + lead nitrateMagnesium + lead nitrate

Nitric acid + calcium Nitric acid + calcium hydroxidehydroxide

Magnesium oxideMagnesium oxide

Magnesium nitrate + leadMagnesium nitrate + lead

Sodium hydroxide + hydrogenSodium hydroxide + hydrogen

Water + calcium nitrateWater + calcium nitrate

• Write the word equations for the descriptions below.1. The copper oxide was added to hot sulphuric acid and it

reacted to give a blue solution of copper sulphate and water.

water+copper sulphate

sulphuric acid+Copper oxide

2. The magnesium was added to hot sulphuric acid and it reacted to give colourless magnesium sulphate solution plus hydrogen

hydrogen+Magnesium sulphate

sulphuric acid+Magnesium

Activity

• Write the word equations for the descriptions below.3. The methane burned in oxygen and it reacted to give

carbon dioxide and water.

water+Carbon dioxide

oxygen+methane

4. The copper metal was placed in the silver nitrate solution. The copper slowly disappeared forming blue copper nitrate solution and needles of silver metal seemed to grow from the surface of the copper

silver+Copper nitrate

Silver nitrate+copper

Activity

Chemical Equations• Step 1: Write down the word equation.• Step 2: Replace words with the chemical formula .• Step 3: Check that there are equal numbers of each

type of atom on both sides of the equation. If not, then balance the equation by using more than one.

• Step 4: Write in the state symbols (s), (l), (g), (aq).

22MgO(s)MgO(s)22Mg(s)Mg(s) +O+O22(g)(g)

22MgOMgO22MgMg ++ OO22

Oxygen doesn’t balance.Need 2 MgO and so need 2 MgOxygen doesn’t balance.Need 2 MgO and so need 2 Mg

MgOMgOMgMg ++ OO22

magnesium oxidemagnesium oxidemagnesium + oxygenmagnesium + oxygen

ProductsProductsReactantsReactants

• Step 1:Step 1: Write down the word equation.• Step 2:Step 2: Replace words with the chemical formula .• Step 3:Step 3: Check that there are equal numbers of each


• Step 4:Step 4: Write in the state symbols (s), (l), (g), (aq).


sodium + watersodium + water hydrogen + sodium hydroxidehydrogen + sodium hydroxide

++ ++

++ ++

++ ++

NaNa HH22OO HH22 NaOHNaOH

22NaNa 22HH22OO 22NaOHNaOHHH22

22Na(s)Na(s) 22HH22O(l)O(l) HH22(g)(g) 22NaOH(aq)NaOH(aq)

Hydrogen doesn’t balance. Hydrogen doesn’t balance. Use 2 HUse 2 H22O, NaOH, 2NaO, NaOH, 2Na

Chemical Equations

• Step 1:Step 1: Write down the word equation.• Step 2:Step 2: Replace words with the chemical formula .• Step 3:Step 3: Check that there are equal numbers of each


• Step 4:Step 4: Write in the state symbols (s), (l), (g), (aq).


magnesium + lead nitratemagnesium + lead nitrate magnesium nitrate + leadmagnesium nitrate + lead

++ ++

++ ++

MgMg Mg(NOMg(NO33))22 PbPb

Mg(s)Mg(s) Pb(NOPb(NO33))22(aq)(aq) Mg(NOMg(NO33))22(aq)(aq) Pb(s)Pb(s)

Already balances. Already balances. Just add state symbolsJust add state symbols

Pb(NOPb(NO33))22

Chemical Equations

• Below are some chemical equations where the formulae are correct but the balancing step has not been done. . Write in appropriate coefficients (numbers) to make them balance.


AgNOAgNO33(aq)(aq) ++ CaClCaCl22(aq)(aq) Ca(NOCa(NO33))22(aq)(aq) + AgCl(s)+ AgCl(s)

CHCH44(g) (g) + O+ O22(g)(g) COCO22(g)(g) ++ H H22O(g)O(g)

Mg(s)Mg(s) ++ AgAg22O(s)O(s) MgO(s)MgO(s) ++ Ag(s) Ag(s)

NaOHNaOH + H+ H22SOSO44(aq)(aq) NaNa22SOSO44(aq)(aq) ++ H H22O(l)O(l)

22

2 2

2

2 2

Activity

Reacting Masses

Conservation of Mass • New substances are made during chemical reactions• However, the same atoms are present before and after

reaction. They have just joined up in different ways.• Because of this the total mass of reactants is always equal

to the total mass of products. • This idea is known as the Law of Conservation of Mass.

Reaction but no

mass change

• There are examples where the mass may seemseem to change during a reaction.

• Eg. In reactions where a gas is given off the mass of the chemicals in the flask will decrease because gas atoms will leave the flask. If we carry the same reaction in a strong sealed container the mass is unchanged.

Mg

HCl

Gas given off.

Mass of chemicals in flask decreases

11.71

Same reaction in sealed container:

No change in mass

Conservation of Mass

Reacting Mass and formula mass

• The formula mass in grams of any substance contains the same number of particlescontains the same number of particles. We call this amount of substance 1 mole.

Atomic Masses: H=1; Mg=24; O=16; C=12; N=14

1 mole of methane molecules12 + (1x4)CH4

1 mole of magnesium oxide24 + 16MgO

1 mole of hydrogen molecules1x2H2

1 mole of nitric acid1+14+(3x16)HNO3

ContainsFormula MassSymbol

Reacting Mass and Equations

• By using the formula masses in grams ( moles) we can deduce what masses of reactants to use and what mass of products will be formed.

carbon + oxygen carbon dioxide

C + O2 CO2

12 + 2 x 16 12+(2x16)

12g 32g 44g

So we need 32g of oxygen to react with 12g of carbon and 44g of carbon dioxide is formed in the reaction.

Atomic masses: C=12; O=16

aluminium + chlorine aluminium chloride

2Al + 3Cl2 2AlCl3

2 x 27 + 3 x 35.5 2x (27+(3x35.5)

54g 106.5g 160.5g

So 54g of aluminium react with 106.5g of chlorine to give 160.5g of aluminium chloride.

Atomic masses: Cl=35.5; Al=27

• What mass of aluminium and chlorine react together?

Activity

magnesium + oxygen

+

+

Atomic masses: Mg=24; O=16

• What mass of magnesium and oxygen react together?

Magnesium oxide

Mg O2 MgO22

2 x 24 2x16 2x(24+16)

48g 32g 80g

So 48g of magnesium react with 32g of oxygen to give 80g of magnesium oxide.

Activity

Sodium + hydrochloric + hydroxide + acid

+ +

Atomic masses: Na = 23 O = 16 H = 1 Cl = 35.5

• What mass of sodium chloride is formed when sodium hydroxide and hydrochloric acid react together?

Sodium chloride

NaOH HCl NaCl

23+1+16 1+35.5 23+35.5

40g 36.5g 58.5g

So 40g of sodium hydroxide react with 36.5g of hydrochloric acid to give 58.5g of sodium chloride.

H2O

water

(2x1)+16

18g

Activity

Step 1 Word EquationWord Equation

Step 2 Replace words with correctcorrect formulaformula.

Step 3 Balance the equation.Balance the equation.

Step 4 Write in formula massesWrite in formula masses.Remember: where the equation shows more than 1 molecule to include this in the calculation.

Step 5 Add gramsAdd grams to the numbers.

• It is important to go through the process in the correct order to avoid mistakes.

Na is the symbol for?

1. Nitrogen

2. Nickel

3. Neodynium

4. Sodium

Which of these does NOTNOT exist as a diatomic molecule (2 bonded atoms)?

1. Nitrogen

2. Oxygen

3. Calcium

4. Chlorine

How many oxygen atoms are represented in the formula Pb(NO3)2?

1. One

2.Two

3.Three

4.Six

What is the formula mass of MgCl2 ?

Mg=24 Cl=35.5

1. 59.5

2. 83.5

3. 95

4. 119

What is the formula mass of Mg(OH)2 ?

Mg=24 O=16 H = 1

1. 41

2. 42

3. 57

4. 58

What is the percentage nitrogen in ammonium sulphate (NH4)2SO4?

1. 21%

2. 42%

3. 63%

4. 84%

What is the formula of a compound containing 1.4g nitrogen and 3.2g of oxygen? (N=14 O=16)

1. N2O

2. NO

3. NO2

4. N2O3

What is the formula of a compound containing 6.5g zinc and 1.6g oxygen?

(Zn=65 O=16)

1. ZnO

2. Zn2O3

3. ZnO2

4. Zn2O

What is the formula of a compound formed between Cr3+ ions and O2- ions?

1. CrO

2. Cr2O3

3. CrO2

4. Cr3O2

What is the formula of a compound formed between Cr3+ ions and OH- ions?

1.CrOH3

2.Cr3OH

3.Cr(OH)3

4.Cr2OH3

What is the word equation for the reaction described below?

A small piece of strontium metal was added to water. It fizzed giving off hydrogen gas leaving an alkaline solution of strontium hydroxide.

1.Strontium + water hydrogen + strontium hydride

2.Strontium + water oxygen + strontium hydroxide

3.Strontium + water hydrogen + strontium hydrate

4.Strontium + water hydrogen + strontium hydroxide

What numbers a - da - d are needed to balance the equation?

Strontium + water hydrogen + strontium hydroxide

aa Sr + bb H2O cc H2 + dd Sr(OH)2

11 aa=1 bb=1 cc=1 dd=1

22 aa=1 bb=2 cc=1 dd=1

33 aa=1 bb=1 cc=2 dd=1

44 aa=1 bb=1 cc=1 dd=2

What is the mass of 2 moles of magnesium nitrate Mg(NO3)2?

1. 86g

2. 134g

3. 148g

4. 296g

How many moles of iron atoms is 280g of iron? (Fe=56)

1. One mole

2. Two moles

3. Four moles

4. Five moles

When iron rusts it forms the iron oxide Fe2O3.

What mass of oxygen reacts with 112g of iron? (Fe=56 O=16)

1. 1g

2. 16g

3. 48g

4. 168g

Hydrogen reacts with chlorine to form hydrogen chloride HCl.

H2 + Cl2 2HCl

What mass of hydrogen chloride will be obtained from 4g of hydrogen gas? (H=1 Cl=35.5)

1 36.5g2 73g3 109.5g4 146g

Imagine that you can see atoms, molecules and ions

What does the world of particles look like?

Which represents the particles in a solid, liquid and gas?

Solids, liquids and gases

What happens to water particles when the liquid freezes?

Which have a definite volume?

Why do gases diffuse?Which have a definite shape?

What happens to the particles when you pour a liquid?

Which can easily be squashed?

What is happening here?

What is happening here?

START FINISH

Mixing water and alcohol

50 cm3

water

50 cm3

alcohol

98 cm3

mixture

41 g50 g

91 g

How can you explain this?

What does a beaker full of water mean?

powdered copper sulfate

spatula being shaken very gently

specks of copper sulfate fall into

the water and

dissolve

water level so high another drop would make the water overflow

How much copper sulfate can be dissolved in a beaker already

completely full of water?

Hard WaterHard Water C3 3.3C3 3.3 What are the What are the advantages and advantages and disadvantages of hard disadvantages of hard water?water?

Did your mum ever have to tell you to wash when you were a kid? Perhaps it would have been more fun if there was more foam?

Foam on this scale needs a big machine! And the right sort of water!

www.dannyk.co.ukwww.dannyk.co.uk

Hard water contains dissolved chemicals which react with soaps. Instead of producing large fluffy bubbles you end up with a greasy scum. Not nice! You can get bubbles but it takes a lot more soap.

Foam machines use modern detergents, not old-fashioned soap. This means you do not get scum. The detergent is also carefully chosen to make sure it does not hurt your eyes – you don’t want to end up crying at the party!

The chemicals in hard water also come out of solution when it evaporates. This can clog up kettles, boilers and washing machines. This hard substance is called scale.

So hard water is a bad thing? Well, yes and no. Hard water has some benefits…

Beer contains a lot of water and beer made in hard water areas tends to be darker and have more flavour than beer made in soft water areas. Some brewers even add chemicals to water to make it hard so that the beer will taste better.

And the calcium and magnesium salts dissolved in the water are useful to the body. Calcium builds strong bones and teeth, and magnesium is essential for a range of chemical reactions in the body. The amount supplied by the water is usually quite small – but every little helps.

Purifying water

Natural water contains ...

• Insoluble impurities such as mud and the remains of plants and animals.

• Soluble impurities such as minerals.• Biological impurities: microorganisms such as

small fresh-water creatures; bacteria.

What do we mean by pure water?

Tap-water must be free from substances harmful to health.

Laboratory water must from free from ALL impurities.

Screening out solid lumps

River water

Screens of progressively finer mesh remove big chunks of solids

Water containing

• Small particles.• Minerals.• Microorganisms.• Pollutants.

Filtering with filter paperdirty water

filter paper

undissolved solids trapped by filter paper

water containing dissolved solids and microorganisms

On an industrial scale, gravel beds are used for filtering instead of paper.

The ions and molecules of dissolved solids are small enough to pass through the pores in the filter paper.

Distillation

Dissolved solids are left behind when water vaporises.

HEAT

boiling water

arrows show steam rising

steam condenses on cold glass

droplets of water

distilled water

Cooling water from tap

Cooling water to sink

kills microbes

Water softening

Hard water

contains Ca2+(aq) and Mg2+(aq) ions

Soft water

Na+(aq) ions replace the Ca2+

(aq) and Mg2+(aq) ions

calcium ion

water molecule

magnesium ion

sodium ion

by adding sodium carbonate

Ca2+ + CO32– CaCO3

Mg2+ + CO32– MgCO3

Waste water containing calcium and magnesium ions

Brine containing sodium ions

Hard water containing calcium and magnesium ions

Softened water containing sodium ions

ion exchange resin

calcium ion

magnesium ion

sodium ion

Ion exchange

Water treatmentWater treatment C3 3.5C3 3.5 How do we make water How do we make water safe to drink?safe to drink?

Welcome to Sungai Wain Rainforest reserve! A paradise for birds, animals, plants, insects and the source of much of the drinking water for Balikpapan city 20 km away.

At least 3000 mm of rain falls onto the forest every year. The ground holds most of the water in the rainforest, acting like a giant sponge. Some escapes into rainforest streams like this one.

The streams join to form the Wain river which drains most of the rainforest.

The smaller Bugis river is little more than a stream itself - but notice how clear the water is.

This is the Wain reservoir on the southern edge of the rainforest. It holds billions of litres of water and feeds the Pertamina pumping station.

The Pertamina pumping station supplies 18 million litres of water a day to Balikpapan through a 20 km long pipeline.

The pumping station works day and night and supplies about a quarter of the city’s water needs.

The rainforest provides a store of water and releases it into the streams and rivers slowly. This ensures Balikpapan is never without clean water.

But cutting trees for foreign customers can make big money. Here a security patrol checks that these loggers have the correct permits.

Because when the tree cover is lost the rain washes soil and silt into the rivers. The silt ends up in the reservoir where it has to be removed.

In Balikpapan itself the water is allowed to settle and then treated with chlorine before it is pumped to people’s houses. Of course, some is also used for fountains in the local park!

Match the water use to the activity

Using the dishwasher

6 litres

16 litres

50 litres

23 litres

75 litres

Flushing the toilet

A quick shower

A relaxing bath

Using the washing machine =

Using the washing machine: 50 litres

Using the dishwasher:16 litres

A relaxing bath: 75 litres

Flushing the toilet:

6 litres

A quick shower: 23 litres

Water fit to drinkWater fit to drinkC3 3.6C3 3.6How can we provide How can we provide clean water for people?clean water for people?

Supplying clean water to rural villages produces a huge improvement in public health. This village has benefited from a scheme that supplies clean water for drinking, cooking and washing and deals with human waste.

This illustrates the problem for many rural villages in India. There is plenty of water - this is the river during the dry season - but the same source is used for drinking water, washing and even getting rid of human wastes. Treating dirty water is expensive and difficult.

This pump supplies clean water for washing. It is fed from a water tower built by the village and so is owned by the people living there.

This is the shower and toilet block for the village. By carefully managing human wastes the water sources in the area are kept unpolluted.

Waste from the toilets passes into a large tank where it is broken down by bacteria into harmless substances. Banana trees are planted around the pit to make use of these. Now that’s what I call organic fruit!

This building houses the water tank and pump which feeds clean water to the showers and homes. Because the river is kept clear of pollution treatment is simple and cheap. A charity has helped to fund the construction of the building but the village contributes labour and land.

An unexpected benefit of clean water? Healthier children who can spend more time at school. This means they can get better jobs and make more money. The whole village benefits.

• In 1990 only 1% of children in rural India had access to clean water supplies and efficient sewerage systems to keep

human faeces out of rivers.

• By 2004 this had risen to 18%.

• Villages with these systems have reduced infant mortality. Mothers are healthier and are less likely to die during childbirth. The whole village’s earning capability improves.

• No other development initiative produces such good results at such low cost.

Brainstorm the list of benefits clean water and sewage treatment brings to people - in India and in the UK.

KS4: Energy Transfer inReactions

Exothermic Reactions

• Examples include:– Burning reactions including the

combustion of fuels.– Detonation of explosives.– Reaction of acids with metals.

Thermit reaction

Magnesium reacting with acid

Exothermic reactions increase in temperature.

Say whether these processes are exothermic.1. Charcoal burning2. A candle burning.3. A kettle boiling4. Ice melting5. A firework exploding

yes

yes

yes

no

no

You have to put heat inin for boiling and melting.

You get heat outout from all the other processes

Activity

• Magnesium + Hydrochloric acid

Gets hot

25o C 45o Cmagnesium

Hydrochloricacid

Heatenergygivenout


• If heat is given out this energy must have come from chemical energy in the starting materials (reactants).

Reactants convert chemical energy to heat energy.

The temperature rises.

25o C45o C


45o C

• Almost immediately the hot reaction products start to lose heat to the surroundings and eventually they return to room temperature.

25o CChemical energy becomes heat energy.

The reaction mixture gets hotter.

Eventually this heat is lost to the surroundings.

It follows that reaction products have less chemical energy than the reactants had to start with.


Ene

rgy

/ kJ

)

Progress of reaction (time)

Energy Level Diagram for an Exothermic Reaction

reactantsReactants have more chemical energy.

Some of this is lost as heat which spreads out into the room.

productsProducts now have less chemical energy than reactants.

Ene

rgy

/ kJ

Progress of reaction

reactants

products

H=negative

Energy Level Diagram for an Exothermic Reaction 2.

H is howmuch energyis given out

H is negativebecause the products have less energy than the reactants.

Energy Level Diagram for an Exothermic Reaction

Exothermic reactions give out energy. There is a temperature rise and H is negative.

Exothermic Reaction - Definition

products

Ene

rgy

/ kJ

)


reactants

H is negative

Activity

Endothermic Reactions

• Endothermic chemical reactions are relatively rare.

• A few reactions that give off gases are highly endothermic - get very cold.

• Dissolving salts in water is another process that is often endothermic.

Endothermic reactions cause a decrease in temperature.

Cools

Heatenergytakenin as the mixture returns back to room temp.

Starts 25°C Cools to 5°C

Ammoniumnitrate

Water

Endothermic reactions cause a decrease in temperature.

Returns to 25°C


• Extra energy is needed in order for endothermic reactions to occur.

• This comes from the thermal energy of the reaction mixture which consequently gets colder.

Reactants convert heat energy into chemical energy as they change into products. The temperature drops.

25o C5o C


25o C

• The cold reaction products start to gain heat from the surroundings and eventually return to room temperature.

5o C The reactants gain energy.25o C

This comes from the substances used in the reaction and the reaction gets cold.

Eventually heat is absorbed from the surroundings and the mixture returns to room temperature.

Overall the chemicals have gained energy.


products

Ene

rgy

/ kJ

)


reactants

H=+

Energy Level Diagram for an Endothermic Process

This is positivebecause the products have more energy than the reactants.

This is howmuch energyis taken in

Endothermic reactions take in energy. There is a temperature drop and H is positive.

Endothermic Reaction Definition

H=+

products

Ene

rgy

/ kJ


reactants

Are these endothermic or exothermic?1. A red glow spread throughout the mixture

and the temperature rose. 2. The mixture bubbled vigorously but the

temperature dropped 150C.3. Hydrazine and hydrogen peroxide react

so explosively and powerfully that they are used to power rockets into space.

4. The decaying grass in the compost maker was considerably above the outside temperature.

exo

endo

exo

exo

Activity

Sketch the two energy diagrams and label exothermic and endothermic as appropriate.

H=+

products

Ene

rgy

/ kJ


reactantsproducts

Ene

rgy

/ kJ

)


reactants

H=-

Activity

Breaking chemical bonds

• Most chemicals will decompose (break up) if we heat them strongly enough.

• This indicates that breaking chemical bonds requires energy – is an endothermic process.

Heat taken in

Energy needed to overcome the

bonding between the atoms

En

erg

y in

ch

emic

als

Energy needed

Making chemical bonds

• It is reasonable to assume that bond making will be the opposite of bond breaking

• Energy will be given out in an exothermic process when bonds are formed.

Heat given out

Energy given out as bonds form between

atoms

En

erg

y in

ch

emic

als

Energy given out

Changes to chemical bonds Endothermic Reactions

• In most chemical reactions some existing bonds are broken (endothermic)

Energy taken in as old bonds break

• But new bonds are made (exothermic)

En

erg

y in

ch

emic

als

reactants

products

Energy given out as new bonds form

H

Overall endothermic in this case

Changes to chemical bonds Exothermic Reactions

• Again some existing bonds are broken (endothermic)

Energy taken in as old bonds break

• And new bonds are formed (exothermic)

En

erg

y in

ch

emic

als

reactants

products

Energy given out as new bonds form

H

Overall exothermic – in this case

Summary – Bond Changes• Where the energy from bond forming exceeds

that needed for bond breaking the reaction is exothermic.

• Where the energy for bond breaking exceeds that from bond forming the reaction is endothermic.

En

erg

y in

ch

emic

als

reactants

products

H

Bo

nd

s b

reak

Bo

nd

fo

rmin

g

En

erg

y in

ch

emic

als

reactants

products

H Bo

nd

s b

reak

Bo

nd

s fo

rm

Exo Endo

• The formation of nitrogen (IV) oxide (formula NO2) from reaction of nitrogen with oxygen in car engines has a H value of +33.2kJ per mol of nitrogen oxide.

1. Write a word equation for the reaction.2. Write a chemical equation for the reaction.3. Is H positive or negative?4. Is the reaction exothermic or endothermic?5. Draw an simple energy diagram for the reaction (not

showing bond breaking and forming.) 6. Which involves the biggest energy change: bond

breaking or bond forming?

Activity

1. Nitrogen + oxygen nitrogen(IV)oxide2. N2 + 2O2 2NO2.3. H positive (+33.2kJ/mol).4. The reaction is endothermic.5. Energy diagram 6. Bond breaking involves

the biggest energy change.products

Ene

rgy

/ kJ


reactants

Answer

• This is an exothermic reaction

Bond Forming

BondBreaking


En

erg

y in

ch

emic

als

OO

OO

H

CHHH

O OOO

C H H H H

O C OO

OH H

H H

H

Burning Methane

• Hydrogen peroxide decomposes as shown:

1. Calculate energy for bond breaking.

2. Calculate the energy from bond making

3. What is the value of H for the reaction shown

O

H H

O

H H

O O

H

H

O O

H

H

O O

Bond Energy (kJ)

H-O 464

O-O 146

O=O 498

Activity

Bond breaking. (endothermic)4(O-H) + 2(O-O)=1856+292 = +2148kJ

Bond forming: (exothermic)4(O-H) + 1(O=O)=1856+498 = -2354kJ

H = +2148 – 2354 = -206kJ

(Exothermic)

O

H H

O

H H

O O

H

H

O O

H

H

O O

Bond Energy (kJ)

H-O 464

O-O 146

O=O 498

Answer

Activation Energy.• Most chemical reactions, including exothermic

reactions, seem to need an input of energy to get the reaction started.

• This fits completely with what we have already explained:

– Before new bonds can be formed we need to break at least some existing chemical bonds.

– This requires an energy input –known as the activation energy (Eactivation energy (Eaa or E Eactact))

– Once an exothermic reaction is underway it can provide its own activation energy (from the bond forming stage) and so sustains the reaction.

Ene

rgy

/ kJ

)


reactants

products

H= -

Activation Energy and Exothermic Reactions

Ea= +Activation energy

Ene

rgy

/ kJ

)


reactants

products

H=+

Ea= +Activation energy

Activation Energy and Endothermic Reactions

Copy the energy diagram and use it to help you explain why garages can store petrol safely but always have notices about not smoking near the petrol pumps.

Ene

rgy

/ kJ

)


Petrol +

oxygen

Carbon dioxide + water

ActivationEnergy

Activity

The reaction is exothermic but requires the Activation energy to be provided before the reaction can get underway.This is necessary to break some of the bonds in the oxygen or petrol before new bonds can start forming.

Ene

rgy

/ kJ

)


Petrol +

oxygen

Carbon dioxide + water

ActivationEnergy

Answer

Copy the summary using the words from the box to fill in the gaps:

endothermic lose positive

exothermic common

1. Exothermic reactions are _____.

2. Reactions that get cold are called _____.

3. Bond forming is an _______ process.

4. Endothermic reactions have a _____ H.

5. In exothermic reactions the chemicals ___ chemical energy. continued

common

endothermic

exothermic

positive

lose

Activity

Copy the summary using the words from the box to fill in the gaps:

more endothermic activation

1. The energy needed to start off a reaction is called the ______ energy

2. In endothermic reactions bond breaking requires ___ energy than is produced by bond forming.

3. Bond breaking is an _________ process.

activation

more

endothermic

Activity

Summary • Exothermic reactions:

– Are common,– Give out heat.– Have a negative H.– Bond forming gives out more energy than

bond breaking consumes.– Have reactants that contain more chemical

energy than the products.• Endothermic reactions – are the opposite!• Bond breaking is endothermic.• Bond forming is exothermic.• Reactions require an activation energy to

help start the bond breaking process.

Which of the following is an endothermic process?

A. Burning woodB. Reacting an acid and alkaliC. Reacting magnesium with acidD. Dissolving ammonium nitrate in water

Which of the following is true for an exothermic process?

products

Ene

rgy

/ kJ


reactants

A. The reactants lose energy to the surroundings

B. The reaction gets coldC. The energy diagram will

be as shownD. The reaction will have a

H that is positive (+).

Which of the following is true when chemical bonds are broken?

A. The process is exothermicB. Energy is given outC. A physical change is occurringD. The reaction will have a H that is

positive(+).

Which of the following is true for an exothermic reaction?

A. Bond breaking involves a bigger energy change than bond making

B. Bond making involves a bigger energy change than bond breaking

C. Bond making involves the same energy change as bond breaking

Which of the following is the activation energy:

A. XB. YC. Z

Hydrogen molecule to hydrogen atoms

2HH2

H + HH–H

Energy input H = +436 kJ/mol

Oxygen atoms to oxygen molecule

2O O2

O=OO + O

Energy output ΔH = –498 kJ/mol

Chlorine molecule to chlorine atoms

2ClCl2

Cl–Cl Cl + Cl

Energy input ΔH = +243 kJ/mol

Nitrogen atoms to nitrogen molecule

2N N2

N + N NN

Energy output ΔH = –945 kJ/mol

Hydrogen + chlorine to hydrogen chloride

H2 + Cl2 2HCl

H–H + Cl–Cl H–Cl + H–Cl

Breaking bonds Making bonds

H–H H + H +436 H + Cl H–Cl –432

Cl–Cl Cl + Cl +243 H + Cl H–Cl –432

Total +679 Total –864

H = +679 – 864 = –185 kJ Exothermic

Hydrogen + oxygen to water

2H2 + O2 2H2O

H–H + H–H + O=O H–O–H + H–O–H


H–H H + H +436 H + O O–H –464

H–H H + H +436 H + O O–H –464

O=O O + O +498 H + O O–H –464

H + O O–H –464


H = +1370 – 1856 = –486 kJ Exothermic

Methane burning

O=C=O + H–O–H + H–O–HH–C–H + O=O + O=O

CH4 + 2O2 CO2 + 2H2O


C–H C + H4 413

+1652 C + O C=O2 805

–1610

O=O O + O2 498

+996 H + O O–H4 464

–1856


H = +2648 – 3466 = –818 kJ Exothermic

H

H

Energy from fuelsEnergy from fuels C3 4.4C3 4.4 Are you an energy hog?Are you an energy hog?

How much energy do you use every day? Probably too

much! But what do we do that needs so much

energy?

Sort these objects from low to high

energy users.

HighLow

Low High

High

Essential

Not needed

LowNow sort the objects from

essential to not needed

Things in here are not needed and use lots of energy - get rid of them first!

Bit of as problem! You need these things but they use lots of energy. Try to use them as little as possible - and buy the most energy efficient ones.

You don’t really need the things here - but they are not using much energy anyway. Look at them after you’ve sorted the high energy ones next door.

OK, these things are essential and they use less energy. Nothing to do down here. Relax!

High

Not needed

Low

Essential

Flame test

No flame colour

Yellow Red Green Lilac

No ions detected

A trace of yellow?

Bright, golden, yellow?

Brightred?

Brick red?

Na+ impurity

Na+ Li+ Ca2+

Ba2+ K+

tests

conclusions

results

Testing for metal ions

by flame test

test unreliable

Add NaOH(aq)

to soln.

Coloured precipitate

No precipitate

White precipitate

Light blue?

Green (slowly turning brown)?

Reddish-brown?

Warm soln. & test for ammonia

NH3 smell; litmus

turns blue

Add more NaOH

solution

Cu2+ Fe2+ Fe3+ Precipitate dissolves

Precipitate insoluble

Al3+ Ca2+ or Mg2+

NH4+

No ammonia

No ions detected

Testing for metal ions with

sodium hydroxide solution

tests

conclusions

results

Instrumental v traditional methods of analysis

What to do

•Slide 3 contains a template for a cube (a net) and six text boxes.

•The faces of the cube describe six facts about instrumental methods of chemical analysis compared with traditional methods.

•There are three advantages and three disadvantages.

•Decide which is the most important advantage of instrumental methods. Drag the text box with +3 to this face of the cube.

•Decide which is the next most important advantage. Drag the +2 box to this face.

•Finally, drag the +1 text box to the least important advantage.

•In the same way, place the –3, –2 and –1 boxes on the three faces that show the disadvantages of modern instrumental methods.

•Print your template. Cut around the outline, fold the white tabs inwards.

•Fold the faces and glue the tabs to make a cube.

Highly accurate

Tests work with very

small quantities

Quick

Users need special training

Results need specialist

interpretation

Usually very

expensive

+3

+2

+1

–3

–2

–1

How to play

1. A group of up to four people play together.

2. Each person has their own dice. (It doesn’t matter if they have chosen different numbers for the faces from others in the group.)

3. All throw their dice together. Each person scores between +3 and –3 according to their dice.

4. The first person to score above +9 is the winner.

5. Keep your own score.

It’s a clean machine It’s a clean machine C3 5.4C3 5.4How can we detect very low levels of How can we detect very low levels of metalsmetals

Jim needs to be careful - as you can see! He suffers from complete kidney failure which means he must be connected to a kidney machine three times a week. Luckily, he’s not scared of heights!

As you can see, Jim needs dialysis three times a week to keep his blood clean.

The kidney machine works by bringing Jim’s blood very close to a special cleaning solution. The blood and solution are separated by a very thin membrane. Wastes pass into the solution and can be flushed away.

This is the solution used in the kidney machine to clean Jim’s blood. It is called dialysate. It is not pure water but contains a very carefully controlled collection of chemicals. In the early days the solution was made with treated tap water.

In the 1970’s people receiving dialysis were healthy for years but then began to suffer from a strange disease. Their blood seemed to be clean but the disease was always fatal. The doctors were mystified and started to talk of a mystery virus - but they could not detect it at all.

Eventually they tracked it down to the water used to make the dialysate. In some areas this contained tiny amounts of aluminium - as low as a few parts per billion! Because kidney patients needed dialysis so often the chemical began to build up in their blood. This was causing the illness.

Modern dialysate is made with aluminium-free water and the kidney machine is checked regularly for even the smallest levels of aluminium. This is done automatically by machines called atomic absorption spectrometers.

Varian IncVarian Inc

• How does the acidity of the water affect the solubility of aluminium?

2 Why might kidney patients in areas with more acid water supplies be first to show the mysterious disease?

2 What is the connection between aluminium in water and acid rain?

2 Why might water companies use atomic absorption spectrometers for?

Cheat! Cheat! C3 5.5C3 5.5 How can we identify How can we identify chemicals?chemicals?

Hello, my name is Dr Jackie Snow. I work for Analytical Chemists Ltd, a company that identifies unknown chemicals in mixtures. We have carried out work for governments, research scientists, food and drink companies and even for the United Nations.

Whenever we are given a new mixture to analyse, the first job is to sort it out. We use a variety of techniques but the most common ones are to do with chromatography. The picture shows our high performance liquid chromatogram (HPLC) and we also use a gas-liquid chromatogram (GLC). In our Bristol offices, we have some ion-exchange chromatography machines and a gel permeation unit.

Varian IncVarian Inc

We do some drug testing work for the Olympic Committee. Our most famous case was Ben Johnson in 1988. He won the Gold Medal for the 100 m sprint at the Seoul Olympics but lost it a few days later when we showed his urine contained samples of a banned substance.

Some companies in the USA test their employees for drug use. They take a small sample of hair and dissolve it in special solvents. The mixture is run through an HPLC machine and then the individual parts are sent to a spectrometer.

We use three different spectrometers – they can use ultraviolet and infrared radiation to identify compounds. We also have a mass spectrometer (MS) that can measure the molecular mass of individual compounds and identify them in that way.

Pure gold bars are not really pure – they contain tiny amounts of other metals called trace metals. Gold from different mines contain different amounts of these metals. This gives them a unique ‘chemical fingerprint’.

During WWII the Nazis stole gold from many countries. They hoped that when it was melted down no-one would be able to trace it. Wrong! Our MS can detect the trace elements and work out where the gold came from. We have been able to return gold to its rightful owners using this technique.

ILNV1.128

We regularly test food and water samples for safety. We regularly test food and water samples for safety. Even small amounts of some metals can be dangerous. Even small amounts of some metals can be dangerous. We even had to close down one set of vegetable We even had to close down one set of vegetable allotments because it was on the site of an old rubbish allotments because it was on the site of an old rubbish dump. We detected tiny amounts of toxic metals in the dump. We detected tiny amounts of toxic metals in the vegetables grown there.vegetables grown there.

We also test organic vegetables to see if any pesticides are present. If they are, the vegetables are not organic – so we can tell if your greengrocer is trying to cheat you by charging extra for ‘organic’ leeks!

Flame test

No flame colour

Yellow Red Green Lilac

No ions detected

A trace of yellow?

Bright, golden, yellow?

Bright red?

Brickred?

Na+ impurity

Na+ Li+ Ca2+

Ba2+ K+

tests

conclusions

results

Testing for metal ions

by flame test

test unreliable

Add NaOH(aq)

to soln.

Coloured precipitate

No precipitate

White precipitate

Lightblue?

Green(slowlyturningbrown)?

Reddish-brown?

Warm soln. & test for ammonia

NH3 smell; litmus

turns blue

Add more NaOH

solution

Cu2+ Fe2+ Fe3+ Precipitate dissolves

Precipitate insoluble

Al3+ Ca2+ or Mg2+

NH4

No ammonia

No ions detected

Testing for metal ions with

sodium hydroxide solution

tests

conclusions

results+

Add dil. HCl

Fizzes No fizz

Lime water test

Add BaCl2(aq)

Lime water milky

Whiteprecipitate

CO3 SO4

White precipitate

Cream precipitate

Yellow precipitate

Add AgNO3(aq) + dil. HNO3

Warm with NaOH(aq)

NH3 smell; litmus

turns blue

No ammonia

NH3 smell; litmus

turns blue

NO3

conclusionstests

results test unreliable

Testing for

negative ions

Add Al powder and warm

NH4 presentCl– Br– I–

+

–2– 2–

What to do1. Be very careful:

• To use tiny amount of each substance.

• Not to mix them up – even a speck.

2. Put 2–3 cm depth of tap-water in a test tube (not distilled water – it’s just to keep the tube cold).

3. Try the test tube in a flame – there should be no flame colour.

4. Damp the bottom of the test tube with distilled water. Use it to pick up a few specks of solid.

5. Introduce the solid into the edge of the Bunsen flame. Note any colour. Don’t keep the test tube there long.

6. Use a different test tube for each solid to avoid contamination.

Flame test

Testing for metal ions with sodium hydroxide solution

What to do

1. Your solid must first be dissolved in distilled water.

2. Put about 2 cm depth of the solution in a test tube (A).

3. Add sodium hydroxide solution carefully, drop by drop (B).

4. Swirl after each drop and look carefully for any precipitate (C).

Testing for carbonate What to do

1.Carefully add dilute HCl to the substance.

2.Carbonates fizz because they give off carbon dioxide.

3.Carry out the lime water test.

• Suck up carbon dioxide using a teat pipette (A).

• Bubble it through a small amount of lime water in a small test tube (B).

• Lime water goes milky if carbon dioxide is present.

Take care• Don’t suck up acid in the pipette: it neutralises

the lime water.• Don’t suck up any carbonate. If it’s a white

powder it will make the lime water look milky.• Use as little lime water as you can: it makes the

test more sensitive.

Testing for sulfate

What to do1. Your sulfate needs to be dissolved in

distilled water.

2. Acidify the solution with dilute HCl.

3. Put about 2 cm depth of the acidified sulfate solution in a test tube (A).

4. Add barium chloride solution (TOXIC) drop by drop (B).

5. Look for a dense white precipitate (barium sulfate) (C).

Testing for halide (chloride, bromide, iodide)

What to do1. Your halide needs to be

dissolved in distilled water.

2. Put about 2 cm depth of halide solution in a test tube (A).

3. Acidify the solution with dilute HNO3.

4. Add silver nitrate solution, drop by drop (B).

5. If a precipitate forms (C) look at its colour to identify your halide.

white chloride

cream bromide

yellow iodide

What to do1. Your nitrate needs to be dissolved

in distilled water.

2. Put about 2 cm depth of solution in a BOILING TUBE. Add a few drops of sodium hydroxide solution.

3. Warm gently to boiling (A).

4. If you notice a smell of ammonia, and litmus paper turns blue, you have an ammonium salt and the nitrate test won’t work properly.

5. If there is no ammonia so far, add a pinch of aluminium powder and boil gently (B).

6. A positive ammonia test now, but not in the earlier step, shows that nitrate is present.

Testing for nitrate

sulfate testSO42–

carbonate testCO32–

nitrate testNO3–

halide testBr–, Cl–, I–

hydroxide precipitation with NaOH

Al3+, Ca2+, Cu2+, Fe2+, Fe3+, Mg2+, NH4

+.

flame testBa2+, Ca2+, K+, Li+, Na+.

ConclusionResultTestIons

Results of analytical tests

The compound is

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