Group trends become explanations via Zeff, shielding and radius

Group 1 gets more reactive down the group; group 7 gets less reactive down the group. Explanation: the outer electron is further from the nucleus / more shielded, so more easily lost.

The same trends, but now derived from effective nuclear charge across a period (increasing Zeff with roughly constant shielding → smaller atoms, higher IE, higher electronegativity) and increasing n down a group. IB requires you to explain discontinuities: the dip from group 2 to group 13 (a p electron is higher in energy than an s electron in the same shell) and from group 15 to group 16 (electron pairing repulsion in a p orbital) — Structure 3.1.7. It also introduces the metallic → amphoteric → acidic oxide continuum across a period (3.1.5), and transition-metal specifics: variable oxidation states from close successive IEs (3.1.9), and colour from d-orbital splitting in complexes with the observed colour complementary to the absorbed colour (3.1.10).

From memorised trends to derived trends, with mandatory anomalies. And the reason for group-1 reactivity is now framed via ionisation energy, which requires R-04's subshell model.

Zeff and shielding require the subshell model.

Explaining trends by "more shells" alone without mentioning nuclear charge and shielding (loses marks); being unable to explain the IE discontinuities; assuming atomic radius increases across a period; saying a solution "is blue because it absorbs blue light".