A set of five species is isoelectronic with the noble-gas configuration of neon (10…
CHEMISTRY · Multi-part · A Level · Chemistry · Periodicity and periodic trends · Periodicity and periodic trends
Problem
A set of five species is isoelectronic with the noble-gas configuration of neon (10 electrons):
O²⁻, F⁻, Na⁺, Mg²⁺, and Al³⁺
Measured ionic radii are provided.
• O²⁻ = 140 pm
• F⁻ = 133 pm
• Na⁺ = 102 pm
• Mg²⁺ = 72 pm
• Al³⁺ = 54 pm
(a) Rank the five ions from smallest to largest effective nuclear attraction experienced by a valence-shell electron. Support your ranking with specific evidence from the data.
(b) Explain how both the number of protons and the presence of inner-shell electrons lead to the size trend observed in the ionic radii.
(c) Among the five ions, predict which would require the greatest amount of energy to remove one additional electron and explain your reasoning.