Experimental measurements give the following values for the electron affinities (EA)…
CHEMISTRY · Multi-part · A Level · Chemistry · Periodicity and periodic trends · Periodicity and periodic trends
Problem
Experimental measurements give the following values for the electron affinities (EA) of two consecutive members of Period 2:
• O(g) + e⁻ → O⁻(g) ΔH = −141 kJ mol⁻¹
• F(g) + e⁻ → F⁻(g) ΔH = −328 kJ mol⁻¹
Neon (Ne) is reported to have a slightly positive EA.
Use the data and your knowledge of atomic structure to analyze the trend in Period 2.
(a) Write the complete ground-state electron configurations for O, F, and Ne using subshell notation (1s², 2s², etc.).
(b) Explain, in terms of effective nuclear charge and shielding, why the process of adding an electron becomes significantly more exothermic when moving from O to F.
(c) Despite a further increase in effective nuclear charge, the EA of Ne is endothermic. Explain why adding an electron to Ne requires an input of energy.
(d) Predict whether the EA of nitrogen is strongly exothermic, weakly exothermic, or endothermic. Justify your prediction with reference to subshell occupancy and electron–electron repulsion.