C2 Topic 1 and 2

C2.1 Mendeleev

• Mendeleev created the periodic table in 1871.

• He arranged elements in order of their properties.

• -groups = down.

• -period= across

• Metals are on the left hand side of the periodic table.

He arranged them by the following properties:

• Atomic mass• Density• Melting Point• Formula of the oxide

Patterns emerged down the groups and across the periods which confirmed his predictions.

C2.2 Structure of the atom

• Atoms are made up of PROTONS, NEUTRONS and ELECTRONS.

• They are found in the positions shown on the diagram.

• Atom is the smallest of particles.

Electron shells

Nucleus containing protons and neutrons

Particle Relative Mass

Relative Charge

Proton 1 +1

Neutron 1 0

Electron 1/1840 -1

Electrons fill shells from the middle in the order of2, 8, 8, 18 (how many elements are in each period)

The group number corresponds to the number of electrons in the outer shell.

C2.3 The Modern Periodic Table• Top number – MASS NUMBER

The number of protons and neutrons

• Bottom number – ATOMIC NUMBER

The number of protons

(also the same as electrons)

Al27

13

Protons = 13Electrons = 13Neutrons = 27-13 = 14

Protons and neutrons are packed together tightly in the nucleus (high density)

Electrons are spread out in shells (low density)

Isotope -Elements with the same number of protons and electrons but different number of neutrons.

C2.4 Electron shells

• Electron located in the shell.

• Electronic configuration = how the electrons are arranged in an atom.

C2.5 Ionic Bonding

• Ionic bonds form between METALS and NON-METALS.

• Ionic bonding involves the transfer of ELECTRONS.

• Metallic Ions are POSITIVELY charged (ANIONS).

• Non-metallic elements are NEGATIVELY charged (CATIONS).

Loose electron +

Common IonsCharged Particles.

To become positively charged an atom must lose electrons. To become negatively charged and atom must gain electrons.

C2.5 Ionic compounds- non metal and a metal.

• Conduct electricity when MOLTEN (melted) and in an AQUEOUS SOLUTION (dissolved in water)

• DO NOT conduct electricity as a SOLID

• Have high MELTING and BOILING points

• Usually SOLID at ROOM TEMPERATURE

Ion = an atom with a positive or negative charge. Cations = metal atoms lose electrons to form positively charged ions called cations. Anions = Non-metal atoms gain electrons to form negatively ions called anions.

Transferring electrons = ionic bonds.

Ionic compounds have a lattice structure, with a regular arrangement of ions, held together by electrostatic forces between oppositely charged ions.

C2.6 Ionic compounds

• Ionic compounds contain ions. Below are some of the common ones.

Compound ions = contain more than one element.

Names of ionic compounds =If the compound contains oxygen it ends with an –ate…..eg….. Iron sulfate = Fe SO4

If no oxygen then they end in an –ide…….Iron Sulfide….FeS

C2.7 Properties of ionic Compounds • Solid = does not conduct electricity

• Liquid = conduct electricity…WHY….ions are free to move around and they are charged.

• Melting points = when a substance changes from solid to liquid.

• Boiling point = changes from a liquid to a gas.

• Ionic substances = high boiling points and high melting points.

• Ionic bonds = strong and lots of them to break so needs lots of energy.

C2.8 Solubility Soluble = substance dissolves. Insoluble = does not dissolveSalt = Acid + alkaliTable explains which salts are soluble and which are not.

2.10 Precipitations. silver nitrate (soluble) + sodium chloride (soluble) → silver chloride (insoluble) + sodium nitrate (soluble)

AgNO3 (aq) + NaCl (aq)→ AgCl (s) + NaNO3 (aq)

Precipitation reaction - An insoluble solid formed when two soluble substances are mixed.

Barium sulfate is used as a ‘barium meal’ to x-ray patients because it is 1. Opaque to x-rays2. Safe to use3. Insoluble so doesn’t enter the blood

C2.10 Precipitates• Precipitates are SALTS that are formed in chemical reactions that DO NOT

DISSOLVE in the solvent used in the reaction.

C2.11 Ion Tests• Ion tests for metals

(ANIONS) are usually done by FLAME TESTS.

• Each ION produces a certain flame colour.

Testing for CATIONS is done through chemical testing.

1. Chloride – add nitric acid and silver nitrate, if a white precipitate forms then chloride ions are present.

2. Sulphate – add hydrochloric acid and barium chloride, if a white precipitate forms then sulphate ions are present.

3. Carbonate – add an acid and if the gas produced turns limewater MILKY the carbonate ions were present.(carbonate release carbon dioxide)

C2 Topic 3 & 4

C2.12 Covalent Compounds

Learn these covalent molecules. Be able to draw them using dot and cross diagrams.

Covalent bond is when a pair of electrons are shared between two atoms forming a molecule.

Methane CH4

Water H2O

Hydrogen H2Carbon Dioxide CO2

Hydrogen Chloride HClOxygen O2

C2.13 Properties of Covalent Substances

Simple Covalent Substances

• Low melting point

• Low boiling point

• Poor conductor of electricity

Why?

• Because there are weak forces between molecules.

Giant Covalent Substances

• High melting point

• High boiling point

Why?

• Because there are strong forces between molecules.

2.13 Diamond vs. Graphite

Diamond• Used to make cutting tools.

• Very hard with strong bonds between molecules.

• Does not conduct electricity because there are no free electrons.

Graphite• Used to make electrodes and

lubricant.

• There are strong forces between molecules within the layers – but there are weak forces between the layers.

• There is one free electron for each carbon atom meaning it can conduct electricity.

Both examples of giant covalent molecules. Both made from CARBON.

C2.15 Miscible or Immiscible?Key definitions

Miscible – Liquids that completely mix to form a solution.

Immiscible – Liquids that do not form a solution but separate into two layers e.g. oil and water.

Separating two immiscible liquidsUse a separating funnel.1. Open the tap and let the lower liquid flow out and collect in a beaker. 2. Close the tap before the upper liquid starts to run out. 3. Change the beaker and then let the other liquid flow out.

Separating two miscible liquidsUse fractional distillation to separate liquid air to form nitrogen and oxygen. Exploits the fact they have different boiling points.

1. Cool air to -200oC to liquefy it. 2. Warm up to -185oC to evaporate the nitrogen and keep the oxygen liquid.

C2.16 ChromatographyUsed to separate mixtures of coloured compounds including inks, dyes and colouring agents in food.

1. A spot of the mixture is placed near the bottom of a piece of chromatography paper and the paper is then placed upright in a suitable solvent, e.g. water.

2. As the solvent soaks up the paper, it carries the mixtures with it.

3. Different components of the mixture will move at different rates.

4. This separates the mixture out.

Rf valuesDifferent chromatograms and the separated components of the mixtures can be identified by calculating the Rf value using the equation:

The Rf value of a particular compound is always the same - if the chromatography has been carried out in the same way. This allows industry to use chromatography to identify compounds in mixtures.

Rf = distance moved by the compound ÷distance moved by the solvent

C2.17 Chemical Classification

Type of bonding

Melting Point Boiling Point Solubility in Water

Conductivity

Ionic High High Most Dissolve Conduct electricity when molten or in solution, not when solid

Simple molecular covalent

low low Some dissolvein water

Do not conduct electricity

Giant molecularcovalent

High High Insoluble Do not conduct exceptgraphite

Metallic High except mercury

High except mercury

Insoluble Good conductors

C2.14 Classifying Substances

Substance Melting Point Boiling Point Electrical Conductivity

Solubility in water

Type of Bonding

Sodium Chloride

High High Yes in solution or molten

Soluble IONIC

Magnesium Sulfate

High High Yes in solution or molten

Soluble IONIC

Hexane Low Low No Insoluble SIMPLE COVALENT

Paraffin Low Low No Insoluble SIMPLE COVALENT

Silicon dioxide High High No Insoluble GIANTCOVALENT

Copper sulphate

High High Yes in solution or molten

Soluble IONIC

Sucrose High High Soluble GIANTCOVALENT

Could you classify these substances based on their properties? Know these examples!

C2.18 Metallic Bonding and Transition MetalsThe structure of metals – a regular arrangement of positive ions surrounded by a sea of delocalised electrons.

Metals are malleable because ions can slide over each other if a large enough force is applied. The electrons hold the ions together meaning the metal spreads out rather than breaks.

Metals conduct electricity because the delocalised electrons are free to move. If a voltage is applied, the electrons all move in the same direction and this is called a current.

Most metals are transition metals and they typically have high melting points and produce coloured compounds.

C2.19 Alkali MetalsAlkali metals are soft with relatively low melting points. Lithium, Sodium and Potassium react with water to form hydroxides (which are alkaline) and hydrogen gas.

Alkali metals get more reactive as you move down the groups because the atoms lower down have more electron shells. This means the outer electron is further away from the nucleus, not held in place as strongly, and easier to lose – making it more reactive.

Lithium + water Lithium Hydroxide + HydrogenSodium + water Sodium Hydroxide + HydrogenPotassium + water Potassium Hydroxide + Hydrogen

C2.20 Halogens

Halogen Colour State at room temperature

Fluorine Pale Yellow Gas

Chlorine Green/yellow Gas

Bromine Brown Liquid

Iodine Grey Solid

Metal + Halogen Metal Halide

Potassium + Bromine Potassium Bromide2K(s) + Br2(l) 2KBr2(S)

Calcium + Chlorine Calcium Chloride2Ca(s) + Cl2(l) 2KCl2(S)

They all follow the same

pattern. Learn them.

C2.21 Displacement of the halogens• Displacement reactions – a more reactive element

will displace (take the place of) a less reactive element.

Potassium Bromide + Chlorine Potassium Chloride

Potassium Chloride + Bromine No reaction

Chlorine is more reactive than

bromine so will displace the

bromine.

Sodium Iodide + Chlorine Potassium Chloride

Sodium Chloride + Iodine No reaction

Chlorine is more reactive than iodine so will displace the

iodine.

C2.22 More halogen reactions

Halogens react with hydrogen to make hydrogen halides which will dissolve in water to make acidic solutions.

Hydrogen + Fluorine Hydrogen FluorideH2(g) + F2(g) 2HF(g)

Hydrogen + Chlorine Hydrogen ChlorideH2(g) + Cl2(g) 2HCl(g)

Salt

Sodium fluoride

Sodium chloride

Sodium bromide

Sodium iodide

Hal

oge

n

Fluorine Reaction Reaction Reaction

Chlorine No reaction

Reaction Reaction

Bromine No reaction

No reaction

Reaction

Iodine No reaction

No reaction

No reaction

Displacement reactions can

be used to work out the

relative reactivity of

halogens.

C2.23 Noble gases

Noble gases are chemically inert(unreactive) because they have a full outer shell of electrons.

Discovery of Noble Gases1. Chemists noticed the

density of nitrogen made in a reaction was different from that of nitrogen in the air.

2. Chemists made a hypothesis about the composition of the air.

3. Chemists performed tests to show the presence of the Noble gases in the air.

Uses of Noble Gases Reason

Xenon and Argon inside filament lamps

To stop the hot filament reacting with oxygen and burning away

Argon and Helium used in welding

To form a blanket over the hot metal to stop it reactingwith oxygen in the air

Argon used in fire extinguishing systems

It is non flammable and can be used to fill a computer server room (for example) if a fire breaks out.

Helium used to fill balloons and air ships

It has low density

Neon in fluorescent lamps Produces a red light when electric current is passed through it under low pressure

C2Topic 5 Chemical Reactions

C2.24 and C2.25 Temperature changes

Keywords

• Endothermic – reaction that takes heat energy in, decreasing the temperature of the reaction mixture and its surroundings

• Exothermic – reaction that releases heat energy, increasing the temperature of the reaction mixture and its surroundings

Facts:

• During a chemical reaction there is usually a transfer of energy between the reactant and the surroundings.

Endothermic

• Not many reactions are endothermic

• E.g.

Sodium hydrogen carbonate + Hydrochloric acid Sodium Chloride + Water + Carbon dioxide

• Other endothermic reactions include:

– Photosynthesis

– Dissolving ammonium nitrate

• Takes in heat energyExothermic

• Gives out heat

• Most reactions are exothermic

• Temperature increase

• All combustion reactions are exothermic

• E.g. Methane + Oxygen

• Explosions – release a lot of heat and gases very quickly

Making/breaking bonds

• Energy needed to break bond

• Energy released when bonds made

C2.26, 2.27 and 2.28 Rates of Reactions and Collision Theory

Keywords

• Rate of reaction – The speed at which a reaction takes place

• Concentration – A measure of how much solute is dissolved in a fixed volume of solvent.

• Surface area– The total area of all the surfaces of an object or substance

Factors affecting Rate

1. Concentration

• More concentrated =

more particles

• More particles = morecollisions = faster reaction

2. Temperature

• Higher temperature = faster reaction

e.g. And egg cooks faster in boiling water than warm water

• Particles have more energy = move faster

– More effective collisions (collide with more energy)

– Collide more frequently

3. Surface area (SA)

• Solid broken up into smaller pieces = larger SA

• Greater surface area = faster reaction

• More surface area = more particles on the surface therefore more frequent collisions

• A = Smaller SA (block)

• B = Larger SA (powder)

Examples

• Fast reactions = Burning, explosions

• Slow reaction = Rusting, apple browning

Catalysts

• Many chemical processes use catalysts

to increase rate of production of products

• Catalysts help to lower

the temperature and pressure needed = less energy needed = saves money

Keywords

• Catalyst – A substance that speeds up the rate of a reaction without being used up in the reaction

• Catalytic converter – Device fitted to car exhausts with a thin layer of transition metal catalyst on a honeycomb structure giving a large surface area.. The catalyst speeds up the reaction to combine Carbon monoxide and unburned petrol into carbon dioxide and water.

C2.29 Catalysts

Catalytic converters

• Reduce pollutants in exhaust gases

• Combine Carbon monoxide (CO) with oxygen

• Carbon dioxide and water released instead

• Contain transition metals (platinum, rhodium or palladium)

• Expensive metals so small amounts used

• Catalyst spread over a honeycomb structure = large Surface Area

• Works faster with the hot gases from the engine heat it up

B2Topic 6 Quantitative Chemistry

C2.30 and 2.31 Relative Mass

RAM

• Compares mass to that of carbon 12

• E.g. Hydrogen is 12X lighter that carbon

RFM

• Sum of all masses in the formula

• E.g.

EF

• Simplest whole number ratio of atoms/ions

• E.g. H2O there are double the number of hydrogens to oxygen

Keywords

• Relative Atomic mass (RAM) – The mean mass of an atom relative to the mass of an atom of carbon-12, which has a mass of 12.

• Empirical formula (EF) – The simplest whole number ration of atoms of each element in a compound

• Molecular formula (MF) - The actual of atoms of each element that combine to make a molecule of a compound.

• Relative formula mass (RFM)– The sumof the relative atomic masses of all the atoms in a formula

B2.32 Percentage composition

• No atoms are lost or made in a chemical reaction.

• They are rearranged into new substances

• You can use relative mass and balanced equations to calculate the mass of a reactant or product.

Percentage by mass of an element

in a compound

A

M100

Number of atoms of element

= X X

C2.33 Yields

Products need to be make as cheaply as possible. Chemists need to make sure the reaction creates as much product as possible.

Theoretical Yield

1. Maximum calculated amount of a product that could be formed from a given amount of reactants.

2. Can be calculated from the balanced equation

3. Assumes all reactant are turned into products and all products harvested

Actual Yield

1. The actual amount of product obtained from a chemical reaction.

Percentage Yield

1. The actual yield divided by the theoretical yield as a percentage

Yield usually less than expected – 3 reasons:

1. Reaction may be incomplete

2. Some product is lost

3. Other unwanted reactions may occur making a different product.

Keywords

Yield – the amount of useful product obtained from a reaction.

C2.34 Waste and Profit

Cost Effective Process

• All factories must consider environmental impacts including disposal of waste.

• Companies want the most profit

• Reactions need to be• High in percentage yield

• All products are useful so there are no waste products (or uses found for waste products – econimically viable)

• Reactions are fast (quick to make lots of product)

Disposal of Waste Products• Industry make many useful substances (cement, pesticides, plastics)• Many of the reactions make waste products: Not useful Must be disposed of following strict laws Expensive to dispose Can cause environmental problems Can cause social problems (house prices drop or unpleasant smells)

Keywords

• By-products – Any product formed in a reaction in addition to the required product

• Waste products – By-products that have no uses