Chapter summary
Atomic Structure, at a glance
Count particles, build electron configurations and read the evidence in ionisation energies.
A-Level 9476 (2026-2027)
Quick revision
Revisit the essentials, then return to an explanation when you need it.
| Term | Definition to write |
|---|---|
| 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). |
| First ionisation energy | The energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous singly charged positive ions: M(g) → M+(g) + e-. |
| Second ionisation energy | The energy required to remove one mole of electrons from one mole of gaseous singly charged positive ions to form one mole of gaseous doubly charged positive ions: M+(g) → M2+(g) + e-. |
| Orbital | A region of space around the nucleus where there is a high probability of finding an electron. Each orbital holds at most two electrons, with opposite spins. |
| Task | Reliable starting point |
|---|---|
| Count particles | p = Z; n = A - Z; e = Z - signed charge. |
| Compare deflection | Direction follows charge. At equal speed and field, compare |q|/m. |
| Count orbital capacity | s: 1 orbital/2 e; p: 3/6; d: 5/10. |
| Form transition-metal cations | Write the neutral configuration, then remove 4s before 3d. |
| Explain first IE | Compare nuclear charge, shielding, distance, subshell and pairing. |
| Read successive IE | A large jump indicates inner-shell removal; count electrons before it. |
Keep the distinctions: isotope versus ion; orbital versus subshell; electron count versus proton number; filling order versus removal order; general periodic trend versus a subshell or pairing exception.
Quick recall
Define isotopes, and say why isotopes of an element react in the same way.