Chapter summary
Particles and Atoms, at a glance
From changes of state to counting the particles in atoms and ions.
O-Level 6092 (2026) / SEC G3 K324 (2027)
Quick revision
Revisit the essentials, then return to an explanation when you need it.
| Term | Definition to write |
|---|---|
| Proton (atomic) number | The number of protons in the nucleus of an atom. |
| Nucleon (mass) number | The total number of protons and neutrons in the nucleus of an atom. |
| Isotopes | Atoms of the same element with the same number of protons but different numbers of neutrons. They have the same chemical properties because they have the same number of electrons (the same electronic configuration). |
Pure only
| Term | Definition to write |
|---|---|
| Diffusion | The net movement of particles from a region of higher concentration to a region of lower concentration, caused by their random motion. |
State changes rearrange particles; heating does not enlarge them. Z counts protons, A counts protons plus neutrons. Isotopes change neutron number; ions change electron number.
| Quantity | Rule |
|---|---|
| Protons | Z |
| Neutrons | A - Z |
| Electrons | Z minus positive charge, or Z plus magnitude of negative charge |
Pure only
Diffusion results from random particle motion. Higher temperature and lower molecular mass generally favour faster gas diffusion.
Quick recall
Describe the arrangement and movement of particles in a liquid.