Chapter summary
The Periodic Table, at a glance
Explain trends from electrons and structure, then predict the oxides, chlorides and redox behaviour of unfamiliar elements.
A-Level 9476 (2026-2027)
Quick revision
Revisit the essentials, then return to an explanation when you need it.
| Observation | Reason |
|---|---|
| Atomic radius falls across Period 3. | Nuclear charge rises with similar inner shielding. |
| Melting point falls sharply after Si. | Giant covalent network changes to discrete molecules. |
| Oxides change basic → amphoteric → acidic. | Bonding and proton-accepting behaviour change across the period. |
| Group 2 carbonates become more stable down the group. | Larger cations polarise carbonate less. |
| Hydrogen halides become less stable down Group 17. | H-X bonds become longer and weaker. |
Remember the exceptions and conditions: Mg/Al and P/S ionisation-energy dips; the ionic-radius jump between cation and anion series; white-phosphorus P4; AlCl3 covalent character; phase-dependent PCl5; partial hydrated-ion hydrolysis rather than automatic hydroxide precipitation.