GCSE Physics resources
AQA GCSE Atomic structure
Atomic notation counts particles; scattering evidence explains why those particles are arranged in a tiny nucleus rather than spread through the atom.
Start here
Atomic notation counts particles; scattering evidence explains why those particles are arranged in a tiny nucleus rather than spread through the atom.
Before you revise
Choose an answer from memory. Your result tells you what to watch for in the guide.
Core revision guide
Atomic notation counts particles; scattering evidence explains why those particles are arranged in a tiny nucleus rather than spread through the atom.
Scope: 8463 and 8464 · Foundation and Higher
Z is proton number and identifies the element. A is protons plus neutrons, so neutrons = A − Z. A neutral atom has Z electrons; losing electrons makes a positive ion without changing its nucleus. Isotopes have the same protons and different neutrons. A typical atom radius is around 10⁻¹⁰ m; its nucleus is much smaller and holds most of its mass.
Scope: 8463 and 8464 · Foundation and Higher
Discovery of electrons ruled out indivisible atoms and led to the plum pudding model: electrons embedded in spread-out positive charge. In the thin-foil experiment, most alpha particles passed straight through, showing that atoms are mostly empty space. A few were strongly deflected or returned backwards, showing a very small, concentrated, positively charged region containing most mass. The spread-out model could not account for those large deflections.
Scope: 8463 and 8464 · Foundation and Higher
Bohr proposed electrons at specific energy levels/distances, consistent with observations; absorbing radiation can raise electron energy and emitting it can lower it. Later work established protons and Chadwick’s work supplied evidence for neutrons in the nucleus. A new model must explain old successful observations as well as the new evidence; detailed Bohr and Chadwick experimental procedures are not required.
Misconception clinic
Read each belief, say what is wrong with it, then compare your correction.
Tempting idea: The nucleus contains electrons.
Use instead: This observation locates empty space, not electrons in the nucleus. Most paths avoid the tiny nucleus.
Tempting idea: 11 protons, 23 neutrons, 11 electrons.
Use instead: A includes protons and neutrons. Neutrons = 23 − 11; neutral electrons = protons.
Retrieval practice
Worked examples
Apply read a and z and distinguish ions in the worked reasoning, then try the changed-context questions below.
Scope: 8463 and 8464 · Foundation and Higher
It has 6 protons, 8 neutrons and 6 electrons.
Scope: 8463 and 8464 · Foundation and Higher
They have the same number of protons but different numbers of neutrons, so they are isotopes of chlorine.
Scope: 8463 and 8464 · Foundation and Higher
Mg²⁺ has 10 electrons.
Exam precision
Do this: Link each observation to its own inference. Use atomic number for protons and mass number minus atomic number for neutrons.
Independent practice
Write an answer before opening the marking guidance. Then edit the exact phrase or step that would gain the next mark.
Scope: 8463 and 8464 · Foundation and Higher
Original PhysicsUK mark scheme: Point 1 (1 mark): Most particles pass through nearly undeflected: atom mostly empty space. Point 2 (1 mark): A few particles are deflected through large angles/backwards. Point 3 (1 mark): These large deflections require concentrated positive charge repelling alpha particles. Point 4 (1 mark): Their rarity shows the nucleus occupies a very small part of the atom; most mass is concentrated there. Award each distinct point once. Accept equivalent scientifically correct wording. No half marks.
Model answer: Most particles pass through, so atoms are mostly empty space. Rare large deflections show a tiny region of concentrated positive charge and mass that repels positive alpha particles.
Scope: 8463 and 8464 · Foundation and Higher
Original PhysicsUK mark scheme: Point 1 (1 mark): Neutrons = 23 − 11 = 12. Point 2 (1 mark): Na⁺ has 10 electrons because it loses one. Award each distinct point once. Accept equivalent scientifically correct wording. No half marks.
Model answer: 12 neutrons; 10 electrons in Na⁺.
Questions pupils ask
Straight paths showed empty space, while rare large deflections required a tiny concentration of positive charge and mass that the plum-pudding model could not explain.
Useful next steps