Question 21 of 48intermediate🔧 ApplyShort Answer2 marks

Consider the following species: N³⁻, O²⁻, F⁻, Na⁺, Mg²⁺ and Al³⁺ (a) What is common in them? (b) Arrange them in the order of increasing ionic radii.

(a)
Answer

All these species are isoelectronic species as they contain the same number of electrons (10 electrons each).

(b)
Answer

The order of increasing ionic radii is: Al3+<Mg2+<Na+<F−<O2−<N3−Al^{3+} < Mg^{2+} < Na^{+} < F^{-} < O^{2-} < N^{3-}.

Explanation

The given species all have 10 electrons, making them isoelectronic. For isoelectronic species, the ionic radius is determined by the nuclear charge. A greater positive nuclear charge pulls the same number of electrons closer to the nucleus, resulting in a smaller radius. Conversely, a lower nuclear charge (or higher negative charge) means less attraction and greater electron repulsion, leading to a larger radius. Therefore, as we move from Al3+Al^{3+} (highest nuclear charge of 13) to N3−N^{3-} (lowest nuclear charge of 7), the ionic radius progressively increases.

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