Top of the Bench papers don't test obscure trivia — they test whether a Year 9 or 10 chemist really knows the KS3 core: particles, the periodic table, reactions, and acids and alkalis, tested at speed and under a bit of friendly pressure. We build our own KS3 chemistry flashcards for Top of the Bench practice, and pulling together the facts that came up again and again across those cards gives a genuinely useful revision list — useful whether or not your child's school still runs a heat this year. For the background on the competition itself, see our full guide to Top of the Bench.

The periodic table underpins more Top of the Bench questions than any other single topic, and most of it comes down to a handful of trends.

  • Group 1 (the alkali metals — lithium, sodium, potassium) react with water to give hydrogen gas and a metal hydroxide, which is why the family is called "alkali" metals — the metal itself isn't an alkali, but what it leaves behind in the water is. Going down the group, the metals get more reactive, softer, and lower-melting: lithium fizzes, sodium melts into a darting ball, potassium bursts into a lilac flame.
  • Group 7 (the halogens — fluorine, chlorine, bromine, iodine) run the opposite way: they get less reactive going down. Fluorine, the smallest, is the most reactive of all — reactive enough to attack glass. At room temperature chlorine is a green gas, bromine an orange-brown liquid (the only liquid non-metal), and iodine a grey solid that gives off a purple vapour on gentle warming.
  • Group 0 (the noble gases — helium, neon, argon) are unreactive, exist as single atoms rather than molecules, and sit in the one column with no metals at all. Helium fills balloons and argon fills light bulbs precisely because nothing happens to them.
  • A period is a row, not a column — elements in the same period have the same number of electron shells, and properties shift from metal on the left to non-metal on the right as you move across.
  • Chemical symbols aren't always the first letter of the English name. Several come from Latin: sodium is Na (natrium), potassium is K (kalium), iron is Fe (ferrum), copper is Cu (cuprum), silver is Ag (argentum), gold is Au (aurum), lead is Pb (plumbum), and mercury is Hg. Writing "S" for sodium is a classic slip — S is sulfur, and no chemical symbol has two capital letters.
  • Metals conduct electricity because their outer electrons are delocalised — free to drift across the whole structure rather than tied to one atom. The same "sea of electrons" picture explains why metals are malleable (hammered into sheets) and ductile (drawn into wires): the layers of positive ions can slide past each other without the structure breaking.
  • An alloy is a mixture, not a compound. Steel (iron plus a little carbon) is harder than pure iron because the different-sized atoms stop the layers sliding — but the atoms keep their own identities and there's no fixed formula.

Atoms, elements, compounds and particle diagrams

  • An element has one kind of atom; a compound has more than one kind, chemically bonded; a mixture just has particles jumbled together, not bonded. Reading a particle diagram is a two-step check: how many kinds of atom, and are they joined or just mixed. A mixture can be separated by physical means (filtering, evaporating, distilling); a compound needs a chemical reaction.
  • A small number after a bracket in a formula, like the 2 in Ca(OH)₂, multiplies everything inside the bracket — so Ca(OH)₂ is one calcium, two oxygens and two hydrogens, five atoms in total. This is exactly what "is this equation balanced?" questions are really testing.
  • Isotopes are atoms of the same element with different numbers of neutrons — same protons (so same element, same reactions), different mass. Chlorine-35 and chlorine-37 are both chlorine; that's why the periodic table shows chlorine's mass as 35.5, an average over the natural mix.
  • A polymer is a very long molecule made of thousands of small molecules (monomers) joined end to end — ethene molecules link up to make polythene, the plastic in carrier bags.
  • Diamond and graphite are allotropes — different structural forms of the same element, carbon. Same atoms, different arrangement, completely different properties: diamond is hard with no free electrons; graphite is soft, slippery and conducts.

Reactions, energy changes and conservation of mass

  • Atoms are never created or destroyed in a reaction, only rearranged — conservation of mass. When magnesium burns and the ash weighs more than the metal did, the extra mass is oxygen captured from the air. When a metal carbonate is heated and loses mass, carbon dioxide has escaped. The trick to any "where did the mass go" question is asking which gas came in or went out.
  • Exothermic reactions release energy to the surroundings (temperature rises); endothermic reactions take energy in (temperature falls). Burning, neutralisation and most metal-plus-acid reactions are exothermic; melting, evaporating and thermal decomposition of a carbonate are endothermic.
  • Thermal decomposition breaks a compound apart using heat alone, with nothing added — heating copper carbonate turns the green powder black as copper oxide forms and carbon dioxide escapes.
  • A catalyst speeds up a reaction and comes out chemically unchanged, so a small amount keeps working indefinitely. It is not a reactant and doesn't appear in the equation.
  • Displacement: a more reactive metal takes the place of a less reactive one in a compound — iron displaces copper from copper sulfate solution, turning the blue solution paler as brown copper forms. A metal can only displace one below it in the reactivity series.
  • A reversible reaction, shown with a double-headed arrow (⇌), can run both ways at once — as fast as product forms, some converts back. Hydrated copper sulfate turning white on heating and blue again with water is the classic KS3 example.

Testing gases and reading observations

  • Hydrogen: a lit splint gives a squeaky pop. Oxygen: a glowing splint relights. Carbon dioxide: it turns limewater milky. Chlorine: it bleaches damp blue litmus paper. Mixing up the lit-splint and glowing-splint tests is one of the most common slips.
  • Metal plus acid gives a salt plus hydrogen; carbonate plus acid gives a salt plus water plus carbon dioxide. These are easy to swap under pressure — the giveaway is whether a carbonate or a bare metal is reacting.
  • A precipitate is an insoluble solid that appears when two clear solutions are mixed and swap partners — the cloudiness when limewater meets carbon dioxide is a familiar example.

Acids, alkalis and everyday chemistry

  • The pH scale runs from 0 (most acidic) to 14 (most alkaline), with 7 neutral — a lower number is more acidic, not less, which trips people up because it looks backwards next to "bigger is stronger."
  • Neutralisation always follows the same pattern: acid + alkali → salt + water. The salt's name borrows the metal from the alkali and a surname from the acid — hydrochloric acid gives chlorides, sulfuric acid gives sulfates, nitric acid gives nitrates.
  • Everyday acid names worth knowing: vinegar is ethanoic acid, lemons and oranges contain citric acid, and sour milk contains lactic acid.
  • Iron rusts only when both oxygen and water are present — take away either one (dry air, or boiled water sealed under oil) and a nail stays bright. Rust is hydrated iron oxide.

The atmosphere and energy

  • Dry air is roughly 78% nitrogen, 21% oxygen, and a mixture of the rest — including only about 0.04% carbon dioxide, despite carbon dioxide's outsized role in climate.
  • The ozone hole and global warming are different problems with different causes. The ozone hole came from CFCs (once used in aerosols and fridges) breaking up ozone high in the atmosphere; global warming comes from rising carbon dioxide and methane trapping heat. Banning CFCs helped the ozone hole; it did nothing for global temperatures.
  • A greenhouse gas absorbs infrared radiated from the ground and sends some of it back down, rather than blocking sunlight coming in — carbon dioxide, methane and water vapour all do this; nitrogen and oxygen don't.

Where these facts come from — and where to go next

This list is built from our own KS3 chemistry flashcard decks written for Top of the Bench-style practice: the general toolkit deck plus themed decks for individual years, including 2025 and 2024. If your child finds any of these facts shaky rather than solid, that's exactly what regular, spaced flashcard review is for — see our guide to preparing for Top of the Bench with spaced repetition.

Knowing a fact once is not the same as being able to recall it instantly under pressure at the bench. For the mistakes that come from almost knowing these facts — the misremembered trend, the swapped test, the confused pair — see Top of the Bench: common mistakes and misconceptions. And if you're curious which of these ideas show up most consistently across different years' themes, Top of the Bench: what keeps coming up every year digs into that pattern directly.

FAQ

Do I need to enter Top of the Bench for this list to be useful?

No. Every fact here is core KS3 chemistry — particles, the periodic table, reactions, acids and alkalis, energy changes and the atmosphere. It's useful revision whether or not your child's school runs a heat this year.

Is this list exhaustive — is this everything a heat could ask?

No single list can promise that, and we wouldn't claim it. What's here are the facts that came up again and again across our own set of Top of the Bench practice cards, spanning the toolkit deck and each yearly themed deck from 2016 to 2025.

My child struggles to remember all these facts — what actually helps?

Spaced repetition, reviewed little and often, works far better than reading a list once. See our companion piece on preparing for Top of the Bench with flashcards for how that works in practice.

Duke Harewood runs aitutors.me and built its KS3 science tutors, including Professor Curie for chemistry.