Flashcards · 7405 · AS Topic 13

Periodicity (AS Level) flashcards

7 cards on AS Topic 13. Pick a subtopic or study them all.

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How is an element’s block (s, p, d or f) decided?: By the sub-shell that holds its highest-energy electron.
Which block are helium and gallium in?: Helium (1s²): s block. Gallium: p block, because its last electron goes into 4p, even though it contains 3d¹⁰.
Why does atomic radius decrease from Na to Cl?: Nuclear charge increases, electrons are added to the same shell so shielding is similar, and the stronger attraction pulls the outer electrons closer.
Why does silicon have the highest melting point in Period 3?: It is macromolecular: many strong covalent bonds must be broken to melt it.
Melting points of P₄, S₈ and Cl₂: order and reason: S₈ > P₄ > Cl₂. Only van der Waals forces are overcome; more electrons per molecule (S₈ 128, P₄ 60, Cl₂ 34) give stronger forces.
Why does the melting point rise from Na to Al?: Ion charge goes +1, +2, +3, delocalised electrons per atom go 1, 2, 3 and the ions get smaller, so metallic bonding gets stronger.
Trend in first ionisation energy across Period 3: A general increase from Na (lowest) to Ar (highest), with small drops at Al and at S.