the periodic table of elements @mohdnorihwan.blogspot.com

8/3/2019 The Periodic Table of Elements @mohdnorihwan.blogspot.com

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Chapter 4

THE PERIODIC TABLEOF ELEMENTS


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Historical developmenty Antoine Lavoisier (1743 1794)

- he drew up a list of simple substances, or elements

- he classified elements into 4 groups

- table Lavoisier not accepted because it contains:

a) Non-elements such as heat and light

b) Compounds such as silica, magnesia, chalk, barita

and alumina

Group I Group II Group III Group IV

Heat Carbon Silver Silica

Oxygen Sulphur Lead Magnesia

Hydrogen Chlorine Tin Chalk

Nitrogen Fluorine Cobalt Barita

Phosphorus Bismulth Alumina

Zinc

Nickel


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y Johann W. Dobereiner (1780 1849)

he observed that certain elements had similarproperties

These elements occur in triads, or groups of three

Each triad, the atomic mass of the middle element is

equal to the average mass of the first and last element

Triad table was not accepted because the table only

true for a few elements only

Triads Lithium Sodium Calcium

Atomic

weight

7 23 39

Average

weight

( 7 + 39 ) 2 = 23 = weight of Sodium


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y John Newlands (1837 1898)

He arranged the elements in order of increasing

nucleon number in horizontal rows

He found that the chemical properties of every eighth

element are similar ( law of octaves )

His pattern not successful because :

a) The law of octaves was only accurate for the first 16

elements ( from Li to Ca )

b) There were no positions allocated for elements yet to be

discovered

Li Be B C N O F

Na Mg Al Si P S Cl

K Ca


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y Lother Meyer (1830 1895)

He stated that the properties of the elements areperiodic. They follow their atomic weights

He devised a method to calculate the atomic volume

of an atom :

Atom volume = mass of t

h

e atom of th

e elementdensity of the element

From the value of the atomic volume, he was able to

plot a graph

of atomic volume against atomic massFrom the graph, he conclude that elements with

similar properties occupy similar positions in their

graphs.


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y Dmitri Mendeleev

He arranged the elements in order of increasing

atomic mass

He was more successful for several reasons :a) He left gaps for elements yet to be discovered. He even

used the table to predict the existence and properties if

undiscovered elements.

b) He changed the order if the chemical properties are not

similar

I II III IV V VI VII VIII

1 H

2 Li Be B C N O F

3 Na Mg Al Si P S Cl

4 K Ca ( ) Ti V Cr Mn Fe,Co,Ni

5 Cu Zn ( ) ( ) As Se Br

6 Rb Sr Y Zr Nb Mo ( ) Ru,Rh,Pd


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y Henry G.J.Moseley (1887-1915)

Afterhe obtaining the proton number of the elements,

he arranged the elements according to the increase

proton numbers

Just like Mendeleev did, he left gaps ( ) for elements

yet to be discovered.Moseley work proved that elements should be

arranged by proton number and not by atomic weight.

This is the way the elements of the Periodic Table are

arranged today


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Modern Periodic Tabley

The elements are arranged in order of increasing protonnumber.

y This order is also related to the electron arrangement of

the elements

y Elements wit

hthe same c

hemical properties are placedin the same group

y Refer to you Periodic Table

y The vertical columns are called group. there are 18

groups in the Periodic Table

y Each member of a group shows similarchemical

properties.

y Physical properties such as density, melting point and

colour may show a gradual change when descending the

group


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y Group 1 elements are called alkali metals

y Group 2 elements are called alkaline earth metalsy Group 17 elements are called halogens

y Group 18 elements are called noble gases

y A block of elements called transition elements

separates Group 2 and Group 13

y The horizontal rows are called periods. There are

seven periods

a) Period 1 has two elements only

b) Periodic 2 and 3 have eight elements each. The first

three periods are called the short periods

c) Periods 4 and 5 have 18 elements each. They

called the long periods


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d) Period 6 has 32 elements. Not all the elements can

be listed on the same horizontal row. These

elements are separated below (Lanthanide Series)

e) Period 7 has 31 elements. Not all the elements can

be listed on the same horizontal row. These

elements are separated below ( Actinide Series )

y All members of the same group have the samenumber of valence electrons.

y Valence electrons are electrons in the outermost

shell

a) Group 1 elements have one valence electron

b) Group 2 elements have two valence electrons

c) Group 17 elements have seven valence electrons


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y The number of valence electrons of Group 1 and

Group 2 elements is the same as its group number

y Except forHelium.

y Elements with more than 2 valence electrons

(groups 13 to 18), the group number = 10 + number

of valence electronsPeriods 1 have one electron shell

Periods 2 have two electron shells

Periods 3 have three electron shells

Periods 4 have four electron shells

y So all elements in the same period have the same

number of filled electron shells


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Group 18 Elementsy

Physical properties

Called noble gas and make up almost 1% of the air

All noble gas do not

a) Dissolve in water

b) Conduct electricityc) Conduct heat

They are monoatomic gases at room temperature

a) Boiling point increase down the group

b) Melting point increase down the group

c) Atomic radius increase down the group

d) Density increase down the group

All noble gas have low melting point and boiling

point compare to other gas because intermolecular

force of attraction is low


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y Chemical properties

Noble gas are unreactive because they have filledouter shells of electrons which are a stable electron

arrangement

He have attained the stable duplet electron

arrangementThe other noble gas have attained the stable octet

electron arrangement

Therefore the noble gases do not need to accept,

donate orshare electrons with other elements

All chemical reactions involve either gaining, losing or

sharing electrons


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Uses of Group 18 Elements

y Helium

Used as super-conductors

Fill airships and weather balloons

y Neon

Used in advertising light

y Argon

Used to fill in light bulbs

y KryptonUsed in laser surgery during eye surgery

y Xenon

Used in lighthouse lamps. It gives a beautiful blue light


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Group 1 Elements

y All element in this group are metals which react with

water to form alkaline solutions

Physical properties

y They are all conductors of electricity

y They have low boiling point and melting point

y - Melting point decrease down the group

- Boiling point decrease down the group

- Electropositivity increase down t

he group

( is a measure of the ability of an atom to lose its valence

electron )

- Hardness decrease down the group

-Density increase down t

he group


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Chemical properties

y The alkali metals are the most reactive group of metals in

the Periodic Table

y The alkali metals atoms achieve the stability of a duplet

or octet by giving away its valence electron and form

positive ion

example: Li Li+ + e

2.1 2

Na Na+ + e

2.8.1 2.8

y The reactivity of alkali metal elements increase down the

group


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y Reaction with Oxygen

1) Alkali metals react with oxygen gas to form metal

oxides

example : Na(s) + O2(g) Na2O

2) Alkali metals react with water to form alkaline metal

hydroxide solutions and hydrogen gas

example : 2K(s) + 2H2O(l) 2KOH(aq) + H2(g)

3) Alkali metal react easily with oxygen and water. To

prevent this, alkali metals are kept in oil

4) The alkali metals become more reavtive down the

group

5) Reaction of K, Rb, Cs, Fr with water is explosive.

Thus ,a very small piece should be used during

experiment


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y Reaction with Halogen

1)R

eaction with

halogen will produce colourless,crystalline ionic salts called halides. Example :-

2Na(s) + Cl2(g) 2NaCl(s)

Sodium + chlorine sodium chloride

2) In the above reaction, every alkali atom will donateone electron to the halogen atom. Every halogen

atom will receive one electron from the alkali atom

Li Li+ + e

Br + e Br -

Li+ + Br- LiBr

3) The increase in reactivity is because.


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Group 17 Elementsy Group 17 elements are also known as halogens

y Halogens exist as diatomic molecules(F2, Cl2, Br2, I2 and

At2)

y Halogens are very reactive elements and naturally exist

as halide salts.

Physical properties

y - melting point increase down the group

- boiling point increase down the group

- density increase down the group- size increase down the group

- electronegativity decrease down the group

(electronegativity measures the ability of an element to

accept electrons)


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y At room temperature.

a) Chlorine is a gas

b) Bromine is a liquidc) Iodine is a solid

y Chlorine, bromine and iodine are

a) Not conductors ofheat

b) Not conductors of electricity

Chemical properties

y Reaction withAluminium

a) no reaction was seen until aluminium was heated

b) Whitish, powdery solid halides were produced

2Al(s) + 3Cl2(g) 2AlCl3(s)

Aluminium chloride


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y Reaction with Other Metals

halogens react with almost all metals in the Periodic

Table to yield metal halides

2Al(s) + 3Br2(g) 2AlBr3(s) aluminium bromide

y Reaction with Hydrogen

halogens react withhydrogen to form halides

H2(g) + Br2(g) 2HBr(g) hydrogen bromide

y Reaction with Other Halogens

the halogen also react among themselves

I2(s) + Cl2(g) 2ICI(s) iodine chloride


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y Reactivity decrease down the group

Safety precautions in handling Halogeny the vapor of fluorine, chlorine and bromine are

poisonous

y Astatine is a hazardous material because it is

radioactivey The following precaution should be taken when handling

halogen:

a) halogen gas and liquid should be handled inside a fume

chamber

b) Safety goggles should be used when handling halogen

fumes

c) Gloves should be used when handling halogen materials


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Elements In A Period

y The horizontal rows of elements in the Periodic Table

are called periods

y The elements are arranged from left to right. Each step

will involve an increase in

a) 1 proton particleb) 1 proton number

c) 1 valence electronElements in

Period 3Na Mg Al Si P S Cl Ar

Protonnumber 11 12 13 14 15 16 17 18

Electron

configuration2.8.1 2.8.2 2.8.3 2.8.4 2.8.5 2.8.6 2.8.7 2.8.8

Valence

electron1 2 3 4 5 6 7 8


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Changes in Properties Across

Period 3y The following properties increase from left to right of each

period

a) Proton numberb) The number of valence electron

c) Electronegativity

y The following properties decreases from left to right

a) Electropositivityb) Radius

c) Melting point

d) Boiling point


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y The elements changes from

a) Solid to gas

b) Metallic to non-metallic

c) Conductor to non-conductor

y Uses of Semi-metals(metalloid) in Industry

1) Silicon is a semi-metal. It is widely used in the

semiconductor industry

2) Silicon is used to make

a) Transistor

b) Diode

c) Electric componentsd) Microchips

3) Germanium is another semi-metal. It is also used

extensively in the electronic industry


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Transition Elements

y The transitional elements lie in between group 2 andgroup 13 in the Periodic Table

y All elements in this block of Periodic Table have similar

properties

Physical propertiesy The transition elements are.

a) Hard

b) Shiny

c) Densey They are good.

a) Conductors ofheat

b) Conductors of electricity


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y They.

a) Are malleable and ductile

b) Have high tensile strength

y The radius of all the transition elements is almost

constant

y The following properties decrease from left to right

a) Boiling point

b) Melting point

y The following increase from left to right

a) Proton number

b) Density

y Electronegativity is low for all the elements. However, it

increase slowly from left to right in the Periodic Table


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Special Characteristic ofTransition Elements

1. Majority of the transition elements have more than one

oxidation number in their compound

Elements Compound Formula Oxidation number

Chromium Potassium dichromate(IV) K2Cr2O7 +6

Chromium(III) chloride CrCl3 +3

Iron Iron(II) chloride FeCl2 +2

Iron(III) chloride FeCl3 +3

Nickel Nickel(II) sulphate NiSO4 +2

Nickel(III) bromide NiBr 3 +3

Copper Copper(I) ch

loride CuCl +1Copper(II) oxide CuO +2


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2. Most transition elements form coloured ions

3. Many of the transition elements are able to form

complex ions

Ions Formula of the ions Colour (aqueous)

Chromate(VI) CrO42- Yellowish

Dichromate(VI) Cr 2O72- Orange

Iron(II) Fe2+ Greenish

Iron(III) Fe3+ Brownish

Copper(II) Cu2+ Bluish

Cobalt(II) Co2+ Pale reddish

Manganate(VII) MnO4- Purple

Elements Complex ion Formula

Copper Copper(II) tetra amine Cu(NH3)42+

Chromium Chromium(III) hexa amine Cr(NH3)63+


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4. Many of the transition elements can act as a catalyst

5. Catalysts are used in chemical reaction to speed up

the rate of a reaction

Precious Stones1. All precious stones have brilliant colours

2. These colours are due to the present of transition

elements in the stones

Transition elements Catalyst used in (process)

Nickel Used in hydrogenation of alkenes to produce alkane and

hydrogenation of margarine

Vanadium(

V) oxide

Used in Contact process to produce sulp

huric acid

Iron Used in Haber process to produce ammonia

Platinum Used in Ostwald process to produce nitrogen oxide and

finally to produce nitric acid


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Uses ofTransition Elements in IndustriesWe use catalysts in industries to speed up manufacturing

processes

Precious stones Colour Transition elements

Emerald Green Nickel, Iron

Ruby Red Chromium

Sapphire Deep blue Iron, Titanium

Turquoise Blue-green, blue, or green Copper

Amethyst Violet Manganese, Iron

Manufacture of Catalyst

A

mmonia IronMargarine Nickel

Sulphuric acid Vanadium(V) oxide

Nitric acid Platinum, Rhodium


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The Importance of Diverse

Elements and Compoundsy The uses of elements in our everyday lives

Elements Uses

Hydrogen, H2 Used to cut or weld metals

Used to hydrogenate palm oil to make margarine

Helium, He Used to fill up weather balloons and air ships

Oxygen, O2 Used during respiration of all living things

Use during the burning or oxidation of materials

Nitrogen, N2 Used to make ammonia

Aluminium,Al Used to make electric cables, alloys, windows and doors

Silicon, Si Used to make microchips

Phosphorus, P Used to make matches

Iron, Fe Used to produce steel which is used to make metal

objects such as cars


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y The uses of compounds

Compounds Uses

Ammonia, NH3 Fertilisers, nitric acid

Silver bromide, AgBr Photographic film

Carbon dioxide, CO2 Fire extinguisher, carbonated drinks

Chlorofluorocarbon,

CFC

Freon in air conditioner and

refrigerator

Ethanol, C2H5OH Liquor and Flavour

Iron(II) sulphate, FeSO4 Iron pills for anaemic patientsMagnesium oxide, MgO Antacid for gastric patients

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