Flashcards · 9620 · AS Topic 13

Periodicity (AS Level) flashcards

10 cards on AS Topic 13, subtopics 3.2.1.1 to 3.2.1.2. Pick a subtopic or study them all.

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How is an element classified into the s, p, d or f block?: By the sub-shell that holds its highest-energy electron (the last electron added in the filling order).
Which blocks do the Period 3 elements belong to?: s block: Na, Mg. p block: Al, Si, P, S, Cl, Ar.
Which block is copper (Z = 29, [Ar] 3d¹⁰ 4s¹) in? Which block is helium in?: Copper: d block (the 4s¹ ending does not change that). Helium: s block, although it sits in Group 0.
Block vs group: Block is a sub-shell type (s, p, d, f); a group is a column. For the s and p blocks the group gives the number of outer electrons.

Why does atomic radius decrease from Na to Cl?: Nuclear charge increases across the period, while the outer electrons stay in the third shell with similar shielding, so they are pulled closer to the nucleus.
Trend in first ionisation energy across Period 3, and the two exceptions: General increase (Na lowest, Ar highest). Drops at Mg → Al (3p electron removed, higher in energy than 3s) and P → S (paired 3p electrons repel).
Order of melting points across Period 3 (highest to lowest): Si > Al > Mg > S > Na > P > Cl > Ar
Why does silicon have the highest melting point in Period 3?: It is macromolecular (giant covalent): melting breaks many strong covalent bonds.
Why does the melting point increase from Na to Al?: Metallic bonding gets stronger: ion charge 1+, 2+, 3+; delocalised electrons per atom 1, 2, 3; and the ions get smaller.
Why is the melting point of S₈ higher than P₄, and P₄ higher than Cl₂?: All are molecular: melting overcomes only van der Waals forces. S₈ has the most electrons per molecule (128, vs 60 for P₄ and 34 for Cl₂), so the strongest forces.