Science 10 – Unit A

Chapter A2 – Elements and Compounds

A2.1 – The Periodic Table

Elements

· There are about , and (made in a lab, not found in nature)

· The elements are organized in a table called the

· based on both their

· elements can be sorted into three classes

·

·

·

· Relating the structure of the atom

· In order to understand the organization of the periodic table, we must review what we know

Particle

PROTONS

NEUTRONS

ELECTRONS

symbol

charge

number in an atom

location

mass

· Subatomic particles and the periodic table

· The elements in the periodic table are

· remember, this number does not change, it is like the ID number for that element

· this is why the number of protons is also called

· The elements also increase according to the mass of the element

· the mass is mostly based on its

· in smaller elements, the number of neutrons is

· since the job of the neutrons is to separate the protons to keep them from repelling each other, it reasons that

· The arrangement of elements into rows corresponds to

· The row number is equal to the number of energy levels into which the electrons are organized

· The three classes of elements, (metals, metalloids and non-metals) are so divided based on

·

·

Metals

· Location on the periodic table: to the

· Physical properties

· COLOUR: most are

· CONDUCTIVITY: most are good conductors of

· ABILITY TO CHANGE SHAPE: most are both

· STATE AT ROOM TEMP: all are

· Chemical properties

· REACTIVITY: varies, as some are and others are

· DURING A CHEMICAL REACTION: metals react by giving away “loose” electrons, which gives them

Non-metals

· Location: to the

· Non-metals vary widely in their properties, and are

· Physical properties

· COLOUR: vary

· CONDUCTIVITY: all are

· STATE AT ROOM TEMP: five are , one (bromine) is and the rest are

· Chemical properties

· REACTIVITY: some are and others,

· FORMATION OF MOLECULES: about half the non-metals exist as

· DURING A CHEMICAL REACTION: non-metals , either by

·

· or by

Metalloids

· Location on the periodic table:

· Properties are

· They rarely

Hydrogen – the exception

· Some periodic tables position hydrogen (element number 1) on the left side

· Other periodic tables position it

· Recall, the elements are classified according to

· the reason hydrogen can be in either spot is because it is capable of

The Periodic Table

· PERIOD (row)

· based on

· the number of elements in each period

· GROUP or FAMILY (column)

· groups of elements with similar chemical and physical properties

· GROUP 1:

· soft, shiny and silver

· very reactive

· form (e.g. table salt)

· examples:

· GROUP 2:

· shiny and silver

· less reactive than Group 1

· produce colourful flames, which is why they

· examples:

· GROUP 17:

· poisonous

· react easily

· examples:

· GROUP 18:

· gases that

· can be made to glow when electricity is passed through them

· examples:

The role of neutrons

· Recall the expression “opposites attract” – this applies to the protons (+) and electrons (-)

· We would expect, since they have all the same charge, that the

· We might also expect, since they have an opposite charge, that

· The job of the neutrons is to prevent either of these things from happening by

· It makes sense then, that larger elements that have more protons,

Isotopes

· While the number of protons in an element never changes, the number of neutrons can vary

· Atoms of the same element that

· We distinguish between different isotopes by writing the name of the element followed by the mass number

· the mass number is

· e.g. carbon-12 and carbon-14 both have 6 protons but vary in their number of neutrons ( )

· One of the pieces of information included on the periodic table for each element is the atomic molar mass

· this can be thought of as the average mass number of

· e.g. the atomic molar mass of carbon is 12.01. From this we can determine that , however there are other isotopes that

· Practice problem: Complete the following table

Isotope

Mass number

Number of protons

Number of neutrons

Most common isotope? (Y/N)

oxygen-18

nitrogen-14

lithium-6

20

10

19

21

13

yes

Electrons and energy levels

· Energy levels are regions around the nucleus

· Different levels can hold a different number of electrons, called

· The lowest energy level and can hold up to

· The next two energy levels

· Beyond that, the pattern is more complicated, so you’re only responsible for the arrangement of the first 20 elements, not the transition metals

Bohr diagrams

· Bohr diagrams are drawing to illustrate elements’ atomic structure

· They use a

· The number of protons and neutrons are

· The electrons are

· The outermost level (or shell) is called and the electrons are

· Drawing Bohr diagrams

· Start by drawing a circle for the nucleus

· Inside the circle,

· Draw rings around the nucleus – the number of rings is the same

· Start placing electrons in the rings remembering the octet rule:

· you must begin

· the first energy level (closest to the nucleus) can fit 2 e-

· the next energy level can fit 8 e-

· the next energy level can fit 8 e-

· electrons will be drawn

· Practice problem

· Draw Bohr diagrams for elements 11 – 18

· Compare these diagrams to the ones above. What do you notice?

· The three elements in Group 1:

· The three elements in Group 18:

· Elements in the same group (family)

· Relating Bohr diagrams to chemical properties

· Compare the two Bohr diagrams to the right

· Fluorine , and as a halogen,

· Neon’s valence shell , and as a noble gas,

· Is there a connection between the number of valence electrons and the reactivity of an element?

· YES! Elements want to adopt the electron arrangement of

· How do non-metals become more stable?

· Recall, non-metals react in a chemical reaction by

· and become like the nearest noble gas

· How do metals become more stable?

· Recall, metals react in a chemical reaction by

· Rather than try to gain seven electrons to fill their valence shell, to become like the nearest noble gas

Atoms vs. ions

· Atoms have the same number of electrons as their atomic number

· since # e- = # p+, the positive charges and negative charges cancel each other out

· atoms therefore have

· Ions are formed

· now, # e- # p+, which means that the

· metal ions form when so they have which gives them

Atom of lithium

3p+ and 3e-

Net charge = 0

Ion of lithium

3p+ and 2e-

Net charge = 1+

· non-metal ions form when so they have which gives them

Atom of oxygen

8p+ and 8e-

Net charge = 0

Ion of oxide

8p+ and 8e-

Net charge = 2-

· Ion charge

· Your periodic table will tell you the charge on that element’s ions

· Some elements do not have an ion listed – this occurs when

· Some metals have more than one ion listed – these are called multi-valent metals, and occur because , but try different strategies to become more stable

· Practice problem: Complete the following table

Element

Metal or non-metal

Number of protons

Number of electrons in an atom

Number of electrons in an ion

Number of electrons gained or lost

Ion charge

calcium

nitrogen

magnesium

chlorine

potassium

fluorine

oxygen

argon

Elements combine to form compounds

· A chemical reaction can occur when a metal atom comes in contact with a non-metal atom

· The metal atom will transfer its electrons to the non-metal, making the metal and the non-metal

· The resulting cation and anion are bonded together in an and form an

· Example – how salt is formed

· An atom of sodium has one valence electron it wants to

· An atom of chlorine has one empty space in its valence shell it wants to

· If you react sodium and chlorine together, you make the compound

A2.2a - Naming Ionic Compounds

IUPAC

· The is a group of scientists responsible for the naming rules for elements and compounds

· the system developed by IUPAC ensures that

Ionic compounds

· Ionic compounds form when electrons transfer from one atom to another

· When the two kinds of ions group together,

· Properties of ionic compounds

· besides forming crystal lattices, ionic compounds have some common properties

· all are

· they are very stable, which means they

· all ionic compounds and the solutions

· Crystal lattices

· Different shapes of crystals are formed by different ratios of cations to anions

· Formula units

· A formula unit is the ratio of cations to anions

· The chemical formula for an ionic compound represents this ratio

· e.g. the formula for sodium chloride is NaCl this indicates that you need

· this makes sense if you recall what you know about the structure of the two ions

· sodium has and the chloride has

· The ratio of cations to anions is based on the number of electrons the metal has to give away, compared to the number of electrons the non-metal has room for

· e.g. calcium fluoride

· calcium

· fluorine only has

· we need

· the formula for calcium fluoride, therefore, is CaF2

· Naming ionic compounds

· The IUPAC system of naming ionic compounds is very simple – it just requires you to

· name the cation first by

· name the anion second by

· the name of the anion is written under the element’s symbol on the periodic table

· e.g. K3N potassium & nitrogen

· e.g. MgF2 magnesium & fluorine

Practice problem:

· Name the following compounds

· Li2S

· Ca3N2

· MgO

· RbI

· Ba3P2

· Name the ionic compound formed during the reaction of:

· aluminium and oxygen

· chlorine and yttrium

· nitrogen and magnesium

· zirconium and sulfur

· Formulas for ionic compounds

· As we saw in the previous examples, the formula for an ionic compound uses the

· Subscripts (small numbers written at the bottom) are used (e.g. in MgCl2 , the 2 indicates that you need 2 chloride ions to accommodate the electrons from the magnesium)

· You do not need a subscript 1 when there is only one of an ion in the formula.

· Lastly, the state of the compound at room temperature is indicated

· (s) = , (l) = , (g) = , and (aq) = which means

· Since all ionic compounds are solid, each formula will be followed by (s), unless they are dissolved in water, (aq)

· The key to writing the correct formula is ensuring your charges are balanced, which means

· Writing formulas for ionic compounds

· Identify the ions and their charges

· Determine the total charges needed to balance (use the lowest common multiple)

· Note the ratio of cations to anions

· Use subscripts to write the formula, if needed

· e.g. calcium nitride

· Ca2+ (gives away 2) and N3- (takes in 3) the lowest common multiple is 6 electrons

· we need 3 calciums and 2 nitrogens to balance charges Ca3N2

Practice problems:

· Write the formulas for the following ionic compounds

· magnesium chloride

· sodium sulfide

· calcium phosphide

· potassium nitride

· calcium fluoride

· Compounds with multivalent metals

· Recall, some elements in the transition metals have more than one possible ion charge –

· In the formula, you can tell which of the ions it is based on

· e.g. copper has two ions, Cu2+ and Cu+ the copper in CuCl2 has to be Cu2+ in order for the charges to be balance

· In the name, the charge of the ion for a multivalent metal is indicated by

· e.g. copper (II) chloride

Practice problems:

·

· Write the formulas for

· iron (III) chloride

· lead (IV) oxide

· copper (I) sulfide

· Write the names for:

· Ni2S(s)

· CuF2(s)

· Cr2S3(s)

· Polyatomic ions

· are made up of several non-metallic atoms joined together, which have a charge as an entire group

· some common polyatomic ions include:

· hydroxide, nitrate, sulfate, carbonate,

· polyatomic ions behave the same way as a simple anion –

· a list of common polyatomic ions is included above your periodic table in your data booklet

· additional rules for polyatomic ions

· Writing formulas for compounds with polyatomic ions

· because we’re treating the ion as one unit, if you need more than one of the ion to balance charges, you must

· e.g. calcium nitrate Ca2+ and NO3- Ca(NO3)2(s)

· if you only need one of the ion,

· e.g. magnesium carbonate Mg2+ and CO32- MgCO3(s)

· Naming compounds with polyatomic ions

· the process is exactly the same as for simple anions except that

· you simply name the metal and the polyatomic ion, as it is listed above your periodic table

· e.g. NaNO3(s) sodium nitrate

· e.g. Ca3(PO4)2(s) calcium phosphate

· one exception: ammonium

· ammonium is , making it the only polyatomic cation

· the formula for ammonium is NH4+ (1+ charge)

· the same rules still apply – you simply name the cation (ammonium) and the anion

· e.g. NH4Cl(s)

Practice problems

·

· Write the formulas for:

· barium hydroxide

· iron (III) carbonate

· copper (I) nitrate

· Write the names for:

· Au(NO3)3(s)

· (NH4)3PO4(s)

· K2SO3(s)

A2.2b - Naming Molecular Compounds

Quick review of ionic compounds

· A result of

· Ionic bonds form between

· Naming: the metal is always first, the non-metal second. The non-metals name is changed to have an “ide” ending

· (e.g. sodium chloride)

· Properties:

· Ionic compounds

· In solution,

· Ionic compounds tend to

· Ionic Bonds

· In ionic bonding, valence electrons are completely transferred from one atom to another.  The result? Ions = Electrically charged atoms.

· Cations are positively charged (Mg2+, H+, Na+)

· Anions are negatively charged (O2-, Cl-)

· The oppositely charged ions are attracted to each other by electrostatic forces.

Molecular compounds

· What happens where there’s no metal to give up electrons?

· An ionic compound can only form if

· How can a non-metal become more stable of there’s no metal? The answer is

· This type of compound is called a molecular compound and is

· Consider the atomic structure of oxygen and fluorine atoms

· The oxygen has room for two more electrons, and the fluorines each have room for one

· Since there are no metals to donate electrons, the three non-metals

· The result is a molecular compound

· The oxygen and fluorines are attached by a

· The name of this compound is

Naming molecular compounds

· Recall, writing the formula for ionic compounds involves balancing the charges, which means

· However in molecular compounds, there is no balancing because both compounds are non-metals with negative charges

· For this reason, the names of molecular compounds have to

· Example

· In these diagrams, carbon is represented by the black spheres and oxygen by the red spheres

· Both these molecules have carbon sharing electrons with oxygen

· one is

· the other is

· If these two gases have different physical and chemical properties, they must – we can’t just name them both carbon oxide

· the first:

· the second:

· Naming molecular compounds

· The two elements are named much the same way as ionic compounds – you name

· However, you need to use prefixes to tell you how many of each element

· e.g. the name carbon dioxide indicates one carbon atom, two oxygen atoms

·

· 1 –

· 2 –

· 3 –

· 4 –

· 5 –

· 6 –

· 7 –

· 8 –

· 9 – (ennea)

· 10 -

·

· one additional rule:

· if there is only one of the FIRST element,

· if there is only one of the SECOND element,

· e.g. SO2(g) is named and H2S(g) is named

Practice problems:

·

· Name the following molecular compounds:

· CO2(g)

· N2O(g)

· PCl3(g)

· CF4(g)

· SeBr2(g)

· Write the formulas for:

· oxygen difluoride gas

· dinitrogen tetrasulfide gas

· sulfur trioxide gas

· solid tetranitrogen decaoxide

Covalent bonds

· The bonds of molecular compounds are called

· Each atom donates half of the electrons to be shared.

· If you think of the electron energy levels as being clouds of negative charge, then

Molecular (Polyatomic) elements

· Some non-metals are so unstable (reactive) on their own that they

· Instead, the atoms group together and

· Several elements are diatomic, meaning these are _____, _____, _____, _____, _____, _____, and _____

· Two elements are polyatomic, meaning these are _____ and _____

· To remind you, the polyatomic elements are all listed

Molecular compounds with common names

· While all molecular compounds have IUPAC names (e.g. ) some are better known by their common names (e.g. )

· Some examples you should know are:

·

· water

· glucose

· sucrose (table sugar)

· methane

· methanol

· ethanol

· ammonia

A note about molecular formulas

· Recall, ionic formulas are called formula units, because they describe

· This means, if it is possible, you should e.g. Mg2O2 should be written as

· Molecular formulas are different

· They describe

· They

· Two different compounds may have the same ratio, but are different substances, e.g. ethyne and benzene

Summary of ionic and molecular compounds

IONIC

MOLECULAR

How to recognize them

Type of bonding

What’s happening to the electrons

What the formula represents

How do you know how many of each element?

A2.3 – Properties and Classification of Ionic and Molecular Compounds

Identifying ionic compounds

· Ionic compounds are easily recognizable by formula or name because it

· Can you recognize an ionic compound based on its properties? Yes!

· Even though there are over a million different ionic compounds that are found in nature, all

Explaining ionic properties

· We’ve already seen some of the properties that ionic compounds share, such as:

·

·

·

·

· These properties can all be explained if you think about the

· Solid at Room Temperature

· The state of a substance at room temperature (about 200C) depends on the

· An ionic bond, which occurs when electrons are transferred, is

· This means that it takes to break the bonds

· At 200C, the particles simply do not have enough energy to separate, as they do in a

· High melting/boiling point

· the strength of the ionic bonds, and the fact that it takes

· also explains why ionic compounds have

· Salt

· Compare that to sugar which

· Form crystalline solids

· The ability to form crystals is not exclusively a property of ionic compounds, for example,

· However, ionic crystals are than sugar crystals

· This is again, due to , and the fact that ionic compounds form from repeating units of , which gives them an organized structure

· Crystal lattices

· Different shapes of crystals are formed by different ratios of cations to anions

· Solubility in water

· All ionic compounds , whereas most molecular compounds are insoluble in water

· To understand this, we have to first explain something about the molecular structure of water

· Water: a polar molecule

· As a molecular compound,

· However, the sharing of those electrons is not done equally

· imagine that the electron pair is like the rope in a tug-of-war

· in some molecular compounds, the electron sharing is like a tug-of-war between identical twins because both atoms the electron pair sits

· in water, however, the tug-of-war is between a large, strong individual ( ) and two small, weak individuals ( ), so the electrons sit

· This unequal sharing of electrons makes the oxygen end of the molecule and the hydrogen end (the symbol δ = “slightly”)

· Because it has a δ- pole and a δ+ pole, we call water

· Molecular compounds that share electrons equally, so do not have a δ- pole and a δ+ pole are called

· Polar solvents such as water will dissolve , because their +/- poles will

· However, non-polar molecules such as , but rather

· Solubility in water

· Because water is polar, when an ionic compound dissolves in it,

· If the attraction is strong enough, the entire solid will dissolve easily in water and we say that the compound is

· If the attraction between ions is stronger than the attraction between the ions and water, then the compound will only dissolve a little bit and we say that it is

· You can determine whether or not an ionic compound is soluble by using a , like the one found in your data booklet

· To use the table, locate the anion (- ion) in the header, read down

· if the cation (+ion) is listed in the top row, , and you should list its state as

· if the cation (+ ion) is listed in the bottom row , and you should list its state as

Practice problems

· Indicate the solubility of each of these substances by recording the state as (aq) if the compound is highly soluble in water, and (s) if the compound is slightly soluble in water

·

· (NH4)2S

· AgCl

· PbSO4

· Sr(OH)2

· PbI4

· CuS

·

· State whether or not the following compounds are very soluble or slightly soluble in water.

·

· potassium carbonate

· iron (II) nitrate

· copper (I) chloride

· barium hydroxide

· ammonium sulfite

· calcium sulfide

· lead (IV) bromide

· Conduct electricity in solution

· Substances that conduct electricity do so because

· When ionic compounds dissolve in water,

· This means that electrons are moving from , and the solutions will conduct an electrical current

· Ionic compounds that are highly soluble and those that are slightly soluble

Properties of molecular compounds

· Recall, molecular compounds are composed of

· The attraction between individual atoms in a molecule but the attraction between neighbouring molecules

· As a result:

· molecular compounds can be

· their melting points are

· some form crystals but they

· while some molecular compounds are soluble in water,

Special properties of water

· Because of its polarity, water has some special properties that

· other molecular compounds that are similar in size and structure to water are

· if water were not polar, it would boil at around -800C that would mean that

· The formation of ice is also a

· The 3D structure of ice crystals results from the unusually strong , and means that:

·

·

A2.4 – Acids & Bases

Acids & bases in your body

· The human body contains several fluids that are either acidic or basic, most of which are located

· saliva – slightly basic to protect your teeth

· stomach acid – contains hydrochloric acid to dissolve food and speed up

· pancreas – located just after the stomach in the digestive tract, produces basic compounds to neutralize any acids left in the food leaving the stomach

· Buffers

· Buffers are compounds that , despite the addition of

· Buffers are important in the body because even a change of 0.1 in the pH of the blood

· Buffers are also found in nature – in Alberta, buffering compounds naturally found in our lakes means we don’t experience

pH

· “pH” stands for the

· the lower the pH, the more hydrogen is present in the solution, and

· a movement of one number on the pH scale corresponds to a

· Practice problems

· How much more acidic is a lemon (pH 3) compared to a tomato (pH 5)?

· While most soaps have a pH of 10, shampoo is “pH balanced” to be gentler on the hair. What does the term “pH balanced” mean in terms of the shampoo’s ingredients?

Properties of acids and bases

ACIDS

BASES

Flavour

Feel

Examples in your home

Examples in the lab

Look for formulas that contain…

Reaction with metals

pH

Reaction with litmus

Universal indicator

pH indicators

· pH indicators are chemicals that turn colour based on the presence and amount of acids or bases in a solution

· litmus paper is used to identify a solution as acidic, neutral or basic, but it does not

· another pH indicator, called universal indicator, is a mixture of chemicals that turn a specific colour for a specific pH

Naming acids

· Two different systems exist for naming acids

· classical names such as “hydrochloric acid” or “sulfuric acid” are the ones still used in labs

· IUPAC names have also been developed to tell you exactly what elements are present in the acid, e.g. “aqueous hydrogen chloride” and “aqueous hydrogen sulfate”

· Three types of acid formulas exist

· hydrogen + non-metal anion (ending in “ide”)

· e.g. HCl(aq) - aqueous hydrogen

· e.g. H2S(aq) – aqueous hydrogen

· hydrogen + polyatomic ion ending in “ate”

· e.g. HClO3(aq) – aqueous hydrogen

· e.g. H2SO4(aq) – aqueous hydrogen

· e.g. HNO3(aq) – aqueous hydrogen

· hydrogen + polyatomic ion ending in “ite”

· e.g. HNO2(aq) – aqueous hydrogen

· e.g. H2SO3(aq) – aqueous hydrogen

· When named using the classical system, they become

· hydro_______ic acid

· e.g. HCl(aq) -

· e.g. H2S(aq) –

· ______ic acid

· e.g. HClO3(aq) –

· e.g. H2SO4(aq) –

· e.g. HNO3(aq) –

· ______ous acid

· e.g. HNO2(aq) –

· e.g. H2SO3(aq) –

· Practice problems

· Complete the following table

· If necessary, consult the polyatomic ions table above your periodic table, or on page 491 of your textbook

Formula

IUPAC name

Classical name

H2CrO4(aq)

aqueous hydrogen chromate

chromic acid

HI(aq)

hydroiodic acid

H3PO4(aq)

CH3COOH(aq)

aqueous hydrogen acetate

chlorous acid

aqueous hydrogen carbonate

boric acid

Naming bases

· Because bases are one type of ionic compound, they are named exactly the same way as any others

· Bases are harder to recognize by their formula, but many

Neutralization

· When an acid and a base react together, their properties cancel each other out

· this is a reaction called

· the products of this reaction are

· E.g. the reaction between hydrochloric acid and sodium hydroxide

· HCl(aq)+ NaOH(aq) H2O(l) +NaCl(aq)

·

A2.5 - Our Chemical Society

Hazardous chemicals

· Thousands of chemicals are classified as hazardous, or as “controlled substances” by the Canadian government, based on

·

· e.g. CFCs are compounds found in aerosol containers and old fridges that

· e.g. benzene is a compound used in the manufacture of plastics, dyes, detergents, and some medicine but has to be controlled due to its

·

· level of toxicity

· addictive properties (e.g. alcohol, nicotine)

Chemistry-related careers

· Many different careers require a knowledge of chemistry, even if the person isn’t a chemist or chemical engineer

· Practice problem:

· With a partner, brainstorm three careers that use chemistry and describe two chemicals used in that career.

Homework

· Check and Reflect A2.4 (p. 69)

· #1 (a, c, e…)

· #3 (b, d, f…)

· #4 (a, c, e…)

· #6, 8