Chapter summary
Particles and Atoms, at a glance
From changes of state to counting the particles in atoms and ions.
SEC G2 Science K223 / K225 (2027)
Quick revision
Revisit the essentials, then return to an explanation when you need it.
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 |