CHEMISTRY · Single correct · A Level · Chemistry · Periodicity and periodic trends · Periodicity and periodic trends
Problem
In the isoelectronic series Na⁺, Mg²⁺, and Al³⁺, which statement best explains why Al³⁺ has the smallest ionic radius?
(a) Al3+ has fewer electron–electron repulsions because it loses three electrons when it forms the ion.
(b) Atomic radius decreases across a period, and aluminum lies furthest to the right of these three elements, so Al3+ is the smallest ion.
(c) Al3+ possesses the greatest nuclear charge, so the same number of electrons is drawn closer to the nucleus.
(d) Al3+ experiences less effective nuclear charge because additional inner-shell shielding occurs.