9.2.6—Variations and trends in 9.2.2, 9.2.3, 9.2.4

Periodicity questions require comparing like properties across related compounds: structure, physical state, hydrolysis, acid–base behaviour and bonding.

Start with the formula and bonding model, then write an equation for the stated reagent or water. The trend becomes meaningful only after the individual cases are identified.

Na₂O is ionic/basic, SiO₂ is giant covalent, and SO₂ is molecular/acidic. Their different structures explain why the same “oxide” label does not imply one behaviour.

Do not rank compounds from the element’s position alone. The actual oxide or chloride formula and structure control the observed reaction.