The data below present measured electron-affinity (EA) values for three second-period elements.
Element
Electron affinity / kJmol−1
N
+7
O
–141
F
–328
(Positive EA indicates an endothermic process.)
(a) Using periodic-trend expectations, predict the qualitative sign and relative magnitude of the electron-affinity value that might have been anticipated for oxygen prior to measurement. Briefly justify your prediction.
(b) Compare the predicted value from part (a) with the actual value in the table. Explain, with detailed reference to subshell electron configurations and interelectronic repulsion, why oxygen’s measured EA deviates from the simple trend.
(c) Identify another element in the periodic table that you would expect to show a similarly anomalous electron-affinity value. Provide a rationale that parallels the explanation in part (b).
(d) Hydrogen forms binary hydrides with both nitrogen and oxygen. Discuss how the differing electron-affinity behavior of N and O influences the acid–base properties of NH3 and H2O in aqueous solution. Support your discussion with arguments based on molecular polarity and bond polarity.
a. Part (a)
b. Part (b)
c. Part (c)
d. Part (d)