GCSE-readyGCSE and International GCSE Chemistry: common mistakes
The wrong answers students pick most often in our Chemistry questions, and why they are wrong. Read these before a test, then open the lesson for anything that surprises you.
Getting started
- Getting started: particles and dissolving
- Not “Salt”. Salt is the solute: the substance that dissolves.
- Not “Salt water”. Salt water is the solution.
- Not “Liquid particles do not move”. Liquid particles do move; diffusion happens in liquids, just more slowly.
- Getting started: atoms, elements, compounds and formulae
- Not “Fluorine”. Fluorine is F.
- Not “O2”. O2 has only oxygen atoms, so it is an element.
- Not “He”. Helium is an element.
- Getting started: chemical reactions and conservation of mass
- Not “Atoms are destroyed”. Atoms are never destroyed in a chemical reaction.
1 Key concepts in chemistry
- How the model of the atom developed
- Not “1”. That is the mass of a proton or neutron.
- Not “−1”. −1 is its relative charge, not its mass.
- Atomic structure
- Not “Atoms with different numbers of protons”. Changing the number of protons changes the element.
- Ionic, covalent and metallic bonding
- Not “Diamond”. Diamond is giant covalent.
- Not “Magnesium oxide”. Magnesium oxide is ionic.
- Not “Copper”. Copper is metallic.
- Ions, ionic formulae and ionic lattices
- Not “NH3”. NH3 is ammonia, a molecule.
- Not “NO3−”. That is nitrate.
- Not “NH4−”. The ammonium ion is positive.
3 Chemical changes
- Neutralisation and salts
- Not “It turns limewater milky”. That is the test for carbon dioxide.
- Not “It relights a glowing splint”. That is the test for oxygen.
- Not “It bleaches damp litmus paper”. That is the test for chlorine.
1(a) to (b) States of matter, and elements, compounds and mixtures
- Elements, compounds and mixtures
- Not “Oxygen”. Oxygen is an element.
- Not “Air”. Air is a mixture.
- Not “Sea water”. Sea water is a mixture.
1(c) to (d) Atomic structure and the Periodic Table
- Atoms, molecules and relative atomic mass
- Not “He”. Helium exists as single atoms.
1(f) to (i) Bonding, structure and electrolysis
- Covalent molecules and their properties
- Not “Larger molecules have more covalent bonds to break when boiling”. Boiling does not break covalent bonds.