GCSE Chemistry topics

How small is an atom?

Atoms are about a ten-millionth of a millimetre across — a scale best handled with powers of ten.

Written against: AQA 8464 5.1.1.5 · Foundation and Higher

Builds on: Atoms, elements & compounds — “Before asking how small an atom is, know what one is.” · Standard form: large numbers (MATH) · Standard form: small numbers (MATH) — “Atomic sizes are written in standard form with negative powers of ten.”

Testing common gases

Identifying a mystery gas with a small, sharp test: a squeaky pop for hydrogen, a relit splint for oxygen, milky limewater for carbon dioxide.

Written against: AQA 8464 5.8.2.1 · AQA 8464 5.8.2.2 · AQA 8464 5.8.2.3 · Foundation and Higher

Builds on: Signs of a chemical reaction — “Each gas test is a tiny reaction with one visible sign.” · Combustion

Acids + carbonates

Acids fizz with carbonates too — but the gas this time is carbon dioxide, and limewater proves it.

Written against: AQA 8464 5.4.2.2 · Foundation and Higher

Builds on: Testing common gases · Acids, alkalis & pH — “Acid chemistry first; the fizz is a special case.”

Moles — counting by weighing

Scaling from grams to numbers of atoms.

Written against: AQA 8464 5.3.2.1 · Higher only

Builds on: Balancing symbol equations · Concentration — “Moles scale the concentration idea down to atoms.” · Standard form: large numbers (MATH) · Rearranging simple formulae (MATH) · Relative formula mass — “Moles are mass divided by relative formula mass, so formula mass comes first.”

Inside the atom

A GCSE peek: atoms have their own parts — protons and neutrons in a tiny nucleus, electrons around it.

Written against: AQA 8464 5.1.1.4 · Foundation and Higher

Builds on: Atoms, elements & compounds — “Splitting the atom's story open only works once the atom itself is familiar.” · How small is an atom? · Forces between charges (PHYS)

Ions — atoms with a charge

A GCSE peek: when an atom loses or gains electrons it becomes charged — an ion. Salts are built from them.

Written against: AQA 8464 5.2.1.2 · Foundation and Higher

Builds on: Inside the atom — “Ions are atoms with electrons missing or gained — you need the electrons.” · Electronic structure — “Dot and cross diagrams move outer-shell electrons, so shells come first.” · The three types of chemical bond

Electrons explain the table

A GCSE peek: the table's shape comes from how electrons arrange themselves — group number matches the outer electrons.

Written against: AQA 8464 5.1.2.1 · Foundation and Higher

Builds on: Groups & periods — “The pattern being explained is groups and periods.” · Inside the atom — “Electron arrangements explain the table — you need the electrons.” · Electronic structure — “Group number is the number of outer-shell electrons, so electronic structure comes first.”

Strong & weak acids

A GCSE peek: two acids at the same concentration can have different pH — some acids simply hold their hydrogen back.

Written against: AQA 8464 5.4.2.5 · Higher only

Builds on: Acids, alkalis & pH — “Strong versus weak refines what 'acidic' means — the scale comes first.” · Measuring pH accurately · The pH scale and neutralisation in terms of ions — “Strength is about how many hydrogen ions an acid releases.” · Concentration in grams per cubic decimetre — “Dilute and concentrated are concentration words, and the topic turns on not confusing them with weak and strong.”

Naming compounds and writing equations

Name a compound from its formula, and write word equations, formulae and balanced symbol equations for every reaction in the course. *Higher tier only (was 5.1.1.1c, Half equations and ionic equations):* Write equations that show only the ions that change, and half equations that show electrons being lost or gained.

Written against: AQA 8464 5.1.1.1 · Foundation and Higher, with some Higher-only content

Builds on: Balancing symbol equations — “Balancing simple equations is the Year 9 skill; GCSE asks for it on every reaction in the course.” · Writing simple formulae — “An equation cannot be balanced until each formula in it is right.” · Naming compounds: -ide and -ate · Ions — atoms with a charge — “Ionic equations are written in ions, so ions have to come first.”

Mixtures and how to separate them

A mixture is not chemically joined, so it can be separated by physical methods: filtration, crystallisation, simple and fractional distillation, and chromatography; choose the right one for a given mixture.

Written against: AQA 8464 5.1.1.2 · Foundation and Higher

Builds on: Separating mixtures — “The KS3 separation methods are the starting set; GCSE adds crystallisation and fractional distillation.” · Compounds vs mixtures — “Physical separation only works because a mixture is not chemically joined.” · Chromatography

How the model of the atom developed

The story from solid spheres to the plum pudding model, the alpha-scattering experiment and the nuclear model, then Bohr's electron orbits, the proton and Chadwick's neutron, as an example of evidence changing a model.

Written against: AQA 8464 5.1.1.3 · Foundation and Higher

Builds on: Atoms, elements & compounds — “The story is about what an atom is, so the atom itself must be familiar.” · Forces between charges (PHYS) · Inside the atom — “The models being compared are built from protons, neutrons and electrons.”

Mass number and isotopes

Mass number counts protons plus neutrons; atoms of one element with different numbers of neutrons are isotopes; work out the protons, neutrons and electrons in any atom or ion.

Written against: AQA 8464 5.1.1.5 · Foundation and Higher

Builds on: Inside the atom — “Mass number counts the protons and neutrons that section introduces.”

Relative atomic mass

The relative atomic mass of an element is a weighted average of its isotopes; calculate it from their percentage abundances.

Written against: AQA 8464 5.1.1.6 · Foundation and Higher

Builds on: Percentages of amounts (MATH) — “A weighted average of isotope masses is a percentages calculation.” · Mass number and isotopes — “The average is taken over isotopes, so isotopes come first.”

Electronic structure

Electrons fill the innermost shells first; write or draw the arrangement for the first twenty elements (sodium is 2,8,1).

Written against: AQA 8464 5.1.1.7 · Foundation and Higher

Builds on: The periodic table · Inside the atom — “Electrons can only be placed in shells once you know how many an atom has.”

How the periodic table developed

Early tables ordered elements by atomic weight and misplaced some; Mendeleev left gaps and swapped some pairs, his predictions were confirmed, and isotopes later explained why weight order sometimes fails.

Written against: AQA 8464 5.1.2.2 · Foundation and Higher

Builds on: Mendeleev's gaps — “Mendeleev's gaps are the centre of the story; GCSE adds what came before and why it was later explained.” · Mass number and isotopes

Metals and non-metals

Metals are the elements that form positive ions; explain the differences between metals and non-metals, and where each sits in the table, from their electron arrangements.

Written against: AQA 8464 5.1.2.3 · Foundation and Higher

Builds on: Properties of metals — “The KS3 checklist of metal properties is what the GCSE explanation has to account for.” · Properties of non-metals — “The same goes for the non-metal checklist.” · Metals to non-metals across a period · Electronic structure — “The explanation is in terms of outer-shell electrons.”

Group 0: the noble gases

The noble gases are unreactive because their outer shells are full; their boiling points rise going down the group.

Written against: AQA 8464 5.1.2.4 · Foundation and Higher

Builds on: Group 0: the noble gases — “"Unreactive" was the KS3 fact; a full outer shell is the GCSE reason.” · Electronic structure — “The reason is the electron arrangement.”

Group 1: the alkali metals

Alkali metals have one outer electron; describe how lithium, sodium and potassium react with oxygen, chlorine and water, and explain why reactivity increases down the group.

Written against: AQA 8464 5.1.2.5 · Foundation and Higher

Builds on: Group 1: the alkali metals — “The reactions with water and the trend are KS3; GCSE adds oxygen, chlorine and the reason.” · Electronic structure — “The single outer electron is the explanation.”

Group 7: the halogens and their trends

Halogens have seven outer electrons and exist as two-atom molecules; melting and boiling points rise and reactivity falls down the group; describe the compounds they form with metals and non-metals.

Written against: AQA 8464 5.1.2.6 · Foundation and Higher

Builds on: Group 7: the halogens — “The family and its reactivity trend are KS3; GCSE adds the molecules, the physical trends and the reason.” · Electronic structure — “Seven outer electrons is the explanation.”

Halogen displacement reactions

A more reactive halogen pushes a less reactive one out of a solution of its salt.

Written against: AQA 8464 5.1.2.6 · Foundation and Higher

Builds on: Displacement reactions — “Metal displacement taught the rule "the more reactive one takes the place"; halogens follow it too.” · Group 7: the halogens — “The reactivity order down Group 7 decides which halogen wins.” · Group 7: the halogens and their trends — “Displacement is the trend in reactivity, put to work.”

The three types of chemical bond

Ionic bonds hold oppositely charged ions together, covalent bonds are shared pairs of electrons and metallic bonds are a shared sea of electrons; which one forms depends on whether the elements are metals or non-metals.

Written against: AQA 8464 5.2.1.1 · Foundation and Higher

Builds on: Forces between charges (PHYS) — “All three bonds are attractions between opposite charges.” · Molecules · Electronic structure — “Bonds form by transferring or sharing outer-shell electrons.” · Metals and non-metals

Ionic compounds: the giant lattice

An ionic compound is a giant regular lattice of ions attracting in all directions; recognise it from a diagram, say what each kind of diagram gets wrong, and read off the simplest formula.

Written against: AQA 8464 5.2.1.3 · Foundation and Higher

Builds on: Particle diagrams of substances · Writing simple formulae · Ions — atoms with a charge — “The lattice is built from the ions that ionic bonding makes.”

Covalent bonds and small molecules

Non-metal atoms bond by sharing pairs of electrons; draw dot and cross diagrams for eight named small molecules, including water, ammonia and methane.

Written against: AQA 8464 5.2.1.4 · Foundation and Higher

Builds on: Molecules — “KS3 said atoms join into molecules; a shared pair of electrons is how.” · Reading chemical formulae · Electronic structure — “Sharing is worked out from the outer-shell electrons.” · The three types of chemical bond

Drawing polymers and giant covalent structures

Show covalent bonds as lines in small molecules, in the repeating unit of a polymer and in part of a giant structure; say what each kind of diagram cannot show, and read a molecular formula from a model.

Written against: AQA 8464 5.2.1.4 · Foundation and Higher

Builds on: Polymers: long-chain molecules — “The repeating unit drawn at GCSE is the "small unit repeated" from KS3.” · Covalent bonds and small molecules — “The lines in these diagrams are the covalent bonds from the first half of the section.”

Metallic bonding

A metal is a giant regular structure of atoms whose outer electrons are free to move through the whole piece; sharing those electrons is what holds it together.

Written against: AQA 8464 5.2.1.5 · Foundation and Higher

Builds on: Properties of metals · The three types of chemical bond — “Metallic bonding is the third of the three bond types in detail.”

States of matter and the forces between particles

Melting and boiling points depend on how strong the forces between particles are, which depends on the bonding; predict the state of a substance at a given temperature from data. *Higher tier only (was 5.2.2.1b, Limits of the simple particle model):* The simple model shows particles as solid spheres with no forces between them, which is why it cannot fully explain changes of state.

Written against: AQA 8464 5.2.2.1 · Foundation and Higher, with some Higher-only content

Builds on: Particle model & states — “The particle pictures of solid, liquid and gas are the model being used.” · Melting & freezing — “Melting was particles breaking free; GCSE asks how strong the forces holding them were.” · Reading heating curves · Limits of the particle model — “Year 9 already teaches where the simple model breaks down; Higher tier asks for it by name.” · The three types of chemical bond

State symbols

Add (s), (l), (g) and (aq) to chemical equations to show the state of each substance.

Written against: AQA 8464 5.2.2.2 · Foundation and Higher

Builds on: Balancing symbol equations — “State symbols are added to the symbol equations that can already be balanced.” · Dissolving & solutions

Properties of ionic compounds

Ionic compounds have high melting points because the lattice has many strong bonds to break, and they conduct electricity only when melted or dissolved, because then the ions can move.

Written against: AQA 8464 5.2.2.3 · Foundation and Higher

Builds on: Melting & freezing · Current around a series loop (PHYS) · Ionic compounds: the giant lattice — “The properties follow from the giant lattice.”

Properties of small molecules

Substances made of small molecules melt and boil easily because only the weak forces between molecules are overcome, not the strong bonds inside them; they do not conduct.

Written against: AQA 8464 5.2.2.4 · Foundation and Higher

Builds on: Boiling vs evaporating · Covalent bonds and small molecules — “The molecules in question are the covalent ones.”

Polymers as very large molecules

Polymer molecules are long chains held together by covalent bonds, and the forces between chains are strong enough to make polymers solid at room temperature.

Written against: AQA 8464 5.2.2.5 · Foundation and Higher

Builds on: Polymers: long-chain molecules — “KS3 introduced the long chain; GCSE explains why it makes a solid.” · Properties of small molecules — “Polymers are the small-molecule story with much larger molecules.”

Giant covalent structures

In diamond, graphite and silicon dioxide every atom is covalently bonded to its neighbours throughout, so these solids have very high melting points.

Written against: AQA 8464 5.2.2.6 · Foundation and Higher

Builds on: Covalent bonds and small molecules — “A giant structure is covalent bonding with no molecule to stop at.” · Properties of small molecules

Properties of metals and alloys

Metals have high melting points and can be bent because their atoms sit in layers that slide; an alloy is harder because different-sized atoms distort the layers.

Written against: AQA 8464 5.2.2.7 · Foundation and Higher

Builds on: Properties of metals — “KS3 listed the metal properties; GCSE explains them.” · Describing properties precisely · Metallic bonding — “The explanation uses the metallic structure.”

Metals as conductors

Metals conduct electricity and heat well because their free electrons carry charge and energy through the structure.

Written against: AQA 8464 5.2.2.8 · Foundation and Higher

Builds on: Properties of metals — “Conducting is on the KS3 checklist of metal properties.” · Conduction: heat through solids (PHYS) · Metallic bonding — “The free electrons come from metallic bonding.”

Diamond

Each carbon atom in diamond makes four covalent bonds, which is why diamond is so hard, melts only at a very high temperature and does not carry a current.

Written against: AQA 8464 5.2.3.1 · Foundation and Higher

Builds on: Giant covalent structures — “Diamond is the first worked example of a giant covalent structure.”

Graphite

Each carbon atom in graphite makes three bonds, forming layers of hexagons with one free electron per atom, which explains its properties, including why it conducts like a metal.

Written against: AQA 8464 5.2.3.2 · Foundation and Higher

Builds on: Giant covalent structures — “Graphite is the second worked example of a giant covalent structure.” · Metallic bonding

Graphene and fullerenes

Graphene is a single layer of graphite; fullerenes are hollow cages and tubes of carbon atoms, including buckminsterfullerene and nanotubes, with uses in electronics and materials.

Written against: AQA 8464 5.2.3.3 · Foundation and Higher

Builds on: Graphite — “Graphene is one layer of graphite, and fullerenes are built from the same rings.”

Relative formula mass

Add up the relative atomic masses in a formula to get its relative formula mass, and use it to find the percentage by mass of an element in a compound.

Written against: AQA 8464 5.3.1.2 · Foundation and Higher

Builds on: Counting atoms in formulae — “Relative formula mass adds up the atoms you can already count in a formula.” · Percentages of amounts (MATH) · Relative atomic mass — “Formula mass is built from relative atomic masses.”

Uncertainty in measurements

Every measurement has some uncertainty; estimate it from the spread of repeat readings around their mean.

Written against: AQA 8464 5.3.1.4 · Foundation and Higher

Builds on: Averages & range (MATH) — “Uncertainty is estimated from the range of repeat readings about their mean.” · Comparing fuels fairly

Reacting masses from equations

Read a balanced equation as a recipe in moles and use it to calculate the mass of a product or reactant from a given mass of another.

Written against: AQA 8464 5.3.2.2 · Higher only

Builds on: Balancing symbol equations — “The mole ratio is read from the balancing numbers.” · Ratio & proportion problems (MATH) — “Scaling a mole ratio up or down is a proportion problem.” · Moles — counting by weighing — “The calculation converts mass to moles and back.”

Using moles to balance equations

Work out the balancing numbers of an equation from the masses that reacted, by converting to moles and finding the simplest whole-number ratio.

Written against: AQA 8464 5.3.2.3 · Higher only

Builds on: Balancing symbol equations — “The answer is a balanced equation, reached from the other direction.” · Ratio notation (MATH) · Moles — counting by weighing — “The masses are first converted to moles.”

Limiting reactants

When one reactant is in excess, the other runs out first and limits how much product can form.

Written against: AQA 8464 5.3.2.4 · Higher only

Builds on: Acids + carbonates · Reacting masses from equations — “The limit is worked out with a reacting-mass calculation.”

Concentration in grams per cubic decimetre

Concentration is how much solute, by mass, is dissolved in each unit volume of solution, in g/dm³; calculate the mass of solute in a known volume.

Written against: AQA 8464 5.3.2.5 · Foundation and Higher, with some Higher-only content

Builds on: Concentration — “KS3 concentration was "amount per volume"; GCSE fixes the units and runs the calculation both ways.” · Rearranging simple formulae (MATH)

Metal oxides: oxidation and reduction

Metals react with oxygen to form oxides; gaining oxygen is oxidation and losing it is reduction.

Written against: AQA 8464 5.4.1.1 · Foundation and Higher

Builds on: Oxidation — “Oxidation as gaining oxygen is KS3; reduction is the same idea run backwards.”

The reactivity series

Order eight named metals, with carbon and hydrogen, by how they react with water and dilute acid; reactivity is how readily a metal forms its positive ion, and a more reactive metal displaces a less reactive one.

Written against: AQA 8464 5.4.1.2 · Foundation and Higher

Builds on: The reactivity series — “The league table of metals is KS3; GCSE names the metals and explains the order.” · Displacement reactions — “Displacement is the evidence the series is built from.” · Acids + metals · Ions — atoms with a charge

Oxidation and reduction as electron transfer

Oxidation is losing electrons and reduction is gaining them; write ionic equations for displacement reactions and say which substance is oxidised and which reduced.

Written against: AQA 8464 5.4.1.4 · AQA 8464 5.4.2.1 · Higher only

Builds on: Displacement reactions — “Displacement reactions are the examples the ionic equations describe.” · Acids + metals — “The reaction being explained is the KS3 one.” · Metal oxides: oxidation and reduction — “The oxygen definition comes first; the electron definition replaces it.” · Ions — atoms with a charge — “Losing and gaining electrons is how ions form.” · Naming compounds and writing equations — “The evidence is written as ionic and half equations.”

Neutralisation and making salts

Acids are neutralised by alkalis and insoluble bases to give a salt and water, and by carbonates to give a salt, water and carbon dioxide; predict the salt and work out its formula from the ions.

Written against: AQA 8464 5.4.2.2 · Foundation and Higher

Builds on: Neutralisation — “Acid plus alkali gives salt plus water is the KS3 rule being widened.” · Naming salts — “Naming the salt from the acid is KS3; working out its formula is the GCSE step.” · Acids + carbonates · Ions — atoms with a charge — “Salt formulae are built by balancing ion charges.”

The pH scale and neutralisation in terms of ions

Acids release hydrogen ions in water and alkalis release hydroxide ions; pH runs from 0 to 14 with 7 neutral, and neutralisation is hydrogen ions and hydroxide ions making water.

Written against: AQA 8464 5.4.2.4 · Foundation and Higher

Builds on: Acids, alkalis & pH — “The pH scale is KS3; GCSE says which ions the numbers are measuring.” · Neutralisation — “Neutralisation is rewritten as one reaction between two ions.” · Ions — atoms with a charge — “Acids and alkalis are now defined by the ions they release.”

Electrolysis: the process

A molten or dissolved ionic compound conducts electricity; passing a current sends positive ions to the negative electrode and negative ions to the positive electrode, where they turn into elements.

Written against: AQA 8464 5.4.3.1 · Foundation and Higher, with some Higher-only content

Builds on: Current around a series loop (PHYS) — “An electrolyte completes a circuit: the current here is ions moving.” · Forces between charges (PHYS) · Properties of ionic compounds — “Electrolysis works only because ions are free to move when molten or dissolved.”

Electrolysis of molten ionic compounds

Electrolysing a molten compound of two elements gives the metal at the negative electrode and the non-metal at the positive electrode; predict the products.

Written against: AQA 8464 5.4.3.2 · Foundation and Higher

Builds on: Electrolysis: the process — “It is the simplest case of the general process.”

Extracting metals by electrolysis

Metals too reactive for carbon are extracted by electrolysis, which uses a great deal of energy; aluminium is made from aluminium oxide dissolved in molten cryolite, and the carbon positive electrode has to be replaced regularly.

Written against: AQA 8464 5.4.3.3 · Foundation and Higher

Builds on: Extracting metals from ores — “Carbon extracts only the less reactive metals; electrolysis is what is left for the rest.” · The reactivity series · Electrolysis of molten ionic compounds — “Aluminium extraction is the electrolysis of a molten compound.”

Electrolysis of solutions in water

In a solution, water supplies its own ions; hydrogen forms at the negative electrode if the metal is more reactive than hydrogen, and oxygen forms at the positive electrode unless a halide is present.

Written against: AQA 8464 5.4.3.4 · Foundation and Higher

Builds on: Testing common gases · Electrolysis: the process — “It is the general process with water's ions added.” · The reactivity series — “What is discharged depends on where the metal sits against hydrogen in the reactivity series.” · Test for chlorine

Half equations at the electrodes

At the negative electrode ions gain electrons (reduction) and at the positive electrode they lose electrons (oxidation); write the half equation for each.

Written against: AQA 8464 5.4.3.5 · Higher only

Builds on: Electrolysis: the process — “The half equations describe what happens at each electrode.” · Oxidation and reduction as electron transfer — “Each electrode reaction is a reduction or an oxidation in electron terms.” · Naming compounds and writing equations — “This is where half equations are used most.”

Exothermic and endothermic reactions

Energy is conserved in reactions; exothermic reactions warm their surroundings and endothermic ones cool them; know examples and everyday uses of each.

Written against: AQA 8464 5.5.1.1 · Foundation and Higher

Builds on: Exothermic & endothermic — “Sorting reactions by temperature change is KS3; GCSE adds where the energy goes.” · Energy is always conserved (PHYS) — “Energy conservation is why the products must hold less energy when the surroundings warm up.” · Comparing fuels fairly

Reaction profiles and activation energy

Particles react only if they collide with enough energy, the activation energy; draw and read an energy diagram showing reactants, products, the activation energy and the overall change.

Written against: AQA 8464 5.5.1.2 · Foundation and Higher

Builds on: Exothermic and endothermic reactions — “The diagram shows whether a reaction is exothermic or endothermic.”

Bond energy calculations

Breaking bonds takes energy in and making bonds gives energy out; calculate the overall energy change of a reaction from supplied bond energies.

Written against: AQA 8464 5.5.1.3 · Higher only

Builds on: Balancing symbol equations · Exothermic and endothermic reactions — “The answer says whether the reaction is exothermic or endothermic.” · Covalent bonds and small molecules — “The calculation counts every covalent bond in the molecules.”

Test for chlorine

Chlorine bleaches damp litmus paper white.

Written against: AQA 8464 5.8.2.4 · Foundation and Higher

Builds on: Testing common gases — “Chlorine is the fourth gas test, added to the three learnt at KS3.” · Using indicators

Rates of reaction

A GCSE peek: reactions go faster when particles collide more often or harder — heat, concentration and surface area all raise the collision rate.

Written against: AQA 8464 5.6.1.3 · Foundation and Higher

Builds on: Gas pressure · Catalysts — “Catalysts opened the speed question; collision theory answers it.” · Concentration · Direct proportion y = kx (MATH) · Reaction profiles and activation energy — “Activation energy was defined with reaction profiles in Paper 1.” · Factors that affect the rate of reaction — “Collision theory is the explanation for the list of factors.”

Earth's early atmosphere

A GCSE peek: the air was not always like this — early volcanoes made a carbon-dioxide-rich sky, and life slowly rewrote the recipe.

Written against: AQA 8464 5.9.1.2 · Foundation and Higher

Builds on: The atmosphere's recipe — “Today's recipe is the puzzle; the early atmosphere is the backstory.” · The carbon cycle

Life-cycle assessment

A GCSE peek: judging a product fairly means costing its whole life — raw materials, making, use and disposal — not just the shelf price.

Written against: AQA 8464 5.10.2.1 · Foundation and Higher

Builds on: Polymers: long-chain molecules · Recycling & finite resources — “Life-cycle assessment is the recycling argument, done formally.”

Making water safe to drink

A GCSE peek: potable water is separation at city scale — sieve, settle, filter, then sterilise; distil only when you must.

Written against: AQA 8464 5.10.1.2 · Foundation and Higher

Builds on: Separating mixtures — “Making water drinkable is separating mixtures, scaled up to a city.” · Recycling & finite resources · Pure substances & mixtures — “"Potable" is not "pure": the chemist's meaning of pure from Year 7.” · Measuring pH accurately

Mean rate of reaction

Rate is how much reactant is used or product made per second; calculate a mean rate from masses or gas volumes and the time taken.

Written against: AQA 8464 5.6.1.1 · Foundation and Higher

Builds on: Gradient as a rate (MATH) — “A rate is "change per second": a gradient read as a rate.” · Conservation of mass

Rate graphs and tangents

Draw and read graphs of amount against time, and draw a tangent to the curve to judge the rate at one moment.

Written against: AQA 8464 5.6.1.1 · Foundation and Higher, with some Higher-only content

Builds on: Gradient as a rate (MATH) — “The slope of the curve at one moment is the rate at that moment.” · Finding a line's equation (MATH) · Mean rate of reaction — “A graph shows how the mean rate changes as the reaction goes on.” · Moles — counting by weighing · Gradient of a curve (MATH)

Factors that affect the rate of reaction

Concentration, gas pressure, surface area, temperature and catalysts all change how fast a reaction goes; recall the effect of each.

Written against: AQA 8464 5.6.1.2 · Foundation and Higher

Builds on: Catalysts — “Catalysts were the first rate factor met at KS3.” · Concentration — “Concentration is the factor the required practical varies.” · Mean rate of reaction — “A factor cannot be said to change the rate until a rate can be measured.”

Catalysts and activation energy

A catalyst speeds up a reaction without being used up by offering a route with a lower activation energy; enzymes are biological catalysts.

Written against: AQA 8464 5.6.1.4 · Foundation and Higher

Builds on: Catalysts — “The two KS3 facts about catalysts are the starting point; GCSE says how they work.” · Enzymes in digestion (BIOL) · Reaction profiles and activation energy — “A catalyst's effect is drawn as a lower hump on a reaction profile.” · How enzymes work (BIOL)

Reversible reactions

In some reactions the products can react to re-form the reactants; changing the conditions changes the direction.

Written against: AQA 8464 5.6.2.1 · Foundation and Higher

Builds on: Chemical reactions & equations — “A reversible reaction is still reactants and products, with the arrow pointing both ways.” · Physical vs chemical change

Energy changes in reversible reactions

If a reversible reaction gives out energy in one direction it takes in exactly the same amount in the other.

Written against: AQA 8464 5.6.2.2 · Foundation and Higher

Builds on: Reversible reactions — “The statement is about the two directions of a reversible reaction.” · Exothermic and endothermic reactions — “It uses the words exothermic and endothermic.”

Equilibrium

In a sealed container a reversible reaction reaches equilibrium, where the forward and backward reactions go at the same rate.

Written against: AQA 8464 5.6.2.3 · Foundation and Higher

Builds on: Reversible reactions — “Only a reversible reaction can reach equilibrium.” · Mean rate of reaction

Le Chatelier's principle

When the conditions of a system at equilibrium are changed, the system shifts to oppose the change; use this to predict what happens.

Written against: AQA 8464 5.6.2.4 · Higher only

Builds on: Equilibrium — “The principle describes how an equilibrium responds.”

Changing concentration at equilibrium

Adding more of a reactant makes more product until equilibrium is restored; removing product pulls the reaction forward.

Written against: AQA 8464 5.6.2.5 · Higher only

Builds on: Concentration · Le Chatelier's principle — “It is the principle applied to concentration.”

Changing temperature at equilibrium

Raising the temperature favours the endothermic direction and lowering it favours the exothermic direction.

Written against: AQA 8464 5.6.2.6 · Higher only

Builds on: Le Chatelier's principle — “It is the principle applied to temperature.” · Energy changes in reversible reactions — “One direction is exothermic and the other endothermic.”

Changing pressure at equilibrium

For gases, raising the pressure favours the side of the equation with fewer molecules.

Written against: AQA 8464 5.6.2.7 · Higher only

Builds on: Gas pressure — “Pressure is gas particles hitting the walls, so fewer molecules means less pressure.” · Balancing symbol equations · Le Chatelier's principle — “It is the principle applied to pressure.”

Crude oil and hydrocarbons

Crude oil is a finite resource formed from ancient plankton buried in mud; it is a mixture of many compounds, most of them hydrocarbons, which contain only hydrogen and carbon.

Written against: AQA 8464 5.7.1.1 · Foundation and Higher

Builds on: Fossil fuels are finite — “How oil formed and why it is finite is KS3; GCSE says what it is made of.” · Pure substances & mixtures

Alkanes

The alkanes are a family of hydrocarbons with the general formula CnH2n+2; name and draw the first four: methane, ethane, propane and butane.

Written against: AQA 8464 5.7.1.1 · Foundation and Higher

Builds on: Substituting into formulae (MATH) · Crude oil and hydrocarbons — “Alkanes are the main hydrocarbons in crude oil.” · Covalent bonds and small molecules — “A displayed formula shows each covalent bond as a line.”

Fractional distillation and petrochemicals

Crude oil is separated into fractions of similar-sized molecules by evaporating it and condensing each fraction at a different height; the fractions become fuels and the raw material for solvents, lubricants, polymers and detergents.

Written against: AQA 8464 5.7.1.2 · Foundation and Higher

Builds on: Separating mixtures — “Fractional distillation is KS3 distillation applied to many liquids at once.” · Boiling vs evaporating · Crude oil and hydrocarbons — “Crude oil is the mixture being separated.” · Mixtures and how to separate them

Hydrocarbon properties and molecule size

Boiling point, viscosity and flammability change in a regular way as hydrocarbon molecules get bigger, which decides how each is used as a fuel.

Written against: AQA 8464 5.7.1.3 · Foundation and Higher

Builds on: Alkanes — “The trend runs along the alkane family.” · Properties of small molecules — “Bigger molecules have stronger forces between them, which is why boiling point rises.”

Complete combustion of hydrocarbons

Burning a hydrocarbon in plenty of air oxidises its carbon and hydrogen to carbon dioxide and water and releases energy; write the balanced equation for a given fuel.

Written against: AQA 8464 5.7.1.3 · Foundation and Higher

Builds on: Combustion — “What burning needs and makes is KS3; GCSE writes it as a balanced equation.” · Balancing symbol equations — “The equation has to be balanced.” · Alkanes — “The fuels being burned are alkanes.”

Cracking

Long hydrocarbon molecules are broken into shorter, more useful ones using heat with a catalyst or with steam, because small-molecule fuels are in higher demand; balance equations for cracking.

Written against: AQA 8464 5.7.1.4 · Foundation and Higher

Builds on: Thermal decomposition · Catalysts · Fractional distillation and petrochemicals — “Cracking deals with the long-chain fractions that distillation produces.”

Alkenes and the bromine water test

Cracking also makes alkenes, which are more reactive than alkanes, change the colour of bromine water, and are the starting material for polymers.

Written against: AQA 8464 5.7.1.4 · Foundation and Higher

Builds on: Polymers: long-chain molecules · Cracking — “Alkenes are a product of cracking.”

Formulations

A formulation is a mixture designed as a useful product, with each ingredient in a measured amount for a purpose; fuels, paints, medicines, alloys and fertilisers are examples.

Written against: AQA 8464 5.8.1.2 · Foundation and Higher

Builds on: Pure substances & mixtures — “A formulation is a mixture, made on purpose.” · Properties of metals and alloys

Chromatography and Rf values

Chromatography separates substances by how they share themselves between a moving solvent and the paper; calculate an Rf value and use it to identify a substance or show that it is pure.

Written against: AQA 8464 5.8.1.3 · Foundation and Higher

Builds on: Chromatography — “Running and reading a chromatogram is KS3; GCSE adds the two phases and the Rf calculation.” · Significant figures (MATH) · Pure substances & mixtures

How oxygen increased

Algae, and later plants, released oxygen by photosynthesis from about 2.7 billion years ago, until there was enough for animals to evolve.

Written against: AQA 8464 5.9.1.3 · Foundation and Higher

Builds on: Photosynthesis — the word equation (BIOL) — “The oxygen came from photosynthesis, first met in biology.” · Earth's early atmosphere — “The early atmosphere is the starting point that oxygen changed.” · The photosynthesis reaction (BIOL)

How carbon dioxide decreased

Carbon dioxide was removed by photosynthesis and by being locked into sedimentary rocks and fossil fuels; explain how limestone, coal, crude oil and natural gas formed.

Written against: AQA 8464 5.9.1.4 · Foundation and Higher

Builds on: The carbon cycle — “The carbon cycle shows the routes by which carbon leaves the air.” · Fossil fuels are finite — “How coal and oil formed is the KS3 half of this section.” · The three rock families · Earth's early atmosphere — “The early atmosphere is where the carbon dioxide started.”

Greenhouse gases

Water vapour, carbon dioxide and methane keep the Earth warm enough for life by letting short-wavelength radiation in and absorbing long-wavelength radiation on its way out.

Written against: AQA 8464 5.9.2.1 · Foundation and Higher

Builds on: Greenhouse effect & climate — “That greenhouse gases hold warmth in is KS3; GCSE explains it with wavelengths.” · Thermal radiation (PHYS) — “The explanation rests on radiation arriving from the Sun and leaving the Earth.”

Human activities and the evidence for climate change

Name two human activities that add carbon dioxide and two that add methane; judge the evidence for human-caused warming, including uncertainty, peer review and biased reporting.

Written against: AQA 8464 5.9.2.2 · Foundation and Higher

Builds on: Greenhouse effect & climate — “The main human sources of carbon dioxide were named at KS3.” · Evidence for climate change (GEOG) · Greenhouse gases — “The gases being added are the greenhouse gases.” · Natural and human causes of climate change (GEOG)

Effects of global climate change

Describe four possible effects of a rising average global temperature and discuss their scale and risk.

Written against: AQA 8464 5.9.2.3 · Foundation and Higher

Builds on: Evidence for climate change (GEOG) · Human activities and the evidence for climate change — “The effects follow from the extra greenhouse gases.” · How climate change affects people and the environment (GEOG)

The carbon footprint

A carbon footprint is the total greenhouse gas emitted over the whole life of a product, service or event; describe ways to reduce it and why they are hard to carry out.

Written against: AQA 8464 5.9.2.4 · Foundation and Higher

Builds on: Responding to climate change (GEOG) · Human activities and the evidence for climate change — “A footprint counts the gases from human activities.” · Life-cycle assessment

Pollutants from burning fuels

Burning fuels can release carbon monoxide, soot, sulfur dioxide and oxides of nitrogen as well as carbon dioxide and water; explain how each forms and predict the products for a given fuel.

Written against: AQA 8464 5.9.3.1 · Foundation and Higher

Builds on: Combustion — “KS3 combustion assumed plenty of oxygen and a clean fuel; pollutants appear when either fails.” · Complete combustion of hydrocarbons — “Complete combustion is the case these pollutants depart from.”

Effects of atmospheric pollutants

Carbon monoxide is a poisonous gas that cannot be seen or smelt; sulfur dioxide and nitrogen oxides cause breathing problems and acid rain; particulates dim the sunlight reaching the ground and harm health.

Written against: AQA 8464 5.9.3.2 · Foundation and Higher

Builds on: Weathering of rocks · Pollutants from burning fuels — “These are the pollutants whose formation was just explained.”

The Earth's resources and sustainable development

People rely on finite and renewable resources; sustainable development meets today's needs without harming future generations; read data on resources from charts and tables.

Written against: AQA 8464 5.10.1.1 · Foundation and Higher

Builds on: What counts as a resource (GEOG) — “Geography has already sorted resources into those that regrow and those that run out.” · Recycling & finite resources — “That the Earth's stores are limited is the KS3 starting point.”

Waste water treatment

Sewage and industrial waste water are cleaned by screening, settling into sludge and effluent, then digesting the sludge without air and treating the effluent with air; compare how easy it is to get drinking water from waste, ground and salt water.

Written against: AQA 8464 5.10.1.3 · Foundation and Higher

Builds on: Separating mixtures · Microbes: friend and foe (BIOL) · Making water safe to drink — “Treated waste water is compared with the other sources of drinking water.”

Phytomining and bioleaching

Copper can be won from low-grade ores by growing plants that absorb metal compounds, or by bacteria that dissolve them; the metal is then recovered by displacement with scrap iron or by electrolysis.

Written against: AQA 8464 5.10.1.4 · Higher only

Builds on: Extracting metals from ores — “These are alternatives to digging ore and heating it with carbon.” · Displacement reactions — “Copper is recovered from solution by displacement with scrap iron.” · Electrolysis of solutions in water