Question 6.3: ELECTRON AFFINITIES Why does nitrogen have a less favorable ...
ELECTRON AFFINITIES
Why does nitrogen have a less favorable (more positive) E_{ea} than its neighbors on either side, C and O?
The magnitude of an element’s E_{ea} depends on the element’s valence-shell electron configuration. The electron configurations of C, N, and O are
Carbon: 1s²2s²2p_{x}^{1}2p_{y}^{1} Nitrogen: 1s²2s²2p_{x}^{1}2p_{y}^{1}2p_{z}^{1}
Oxygen: : 1s²2s²2p_{x}²2p_{y}^{1}2p_{z}^{1}
Carbon has only two electrons in its 2p subshell and can readily accept another in its vacant 2p_{z} orbital. Nitrogen, however, has a half-filled 2p subshell, so the additional electron must pair up in a 2p orbital where it feels a repulsion from the electron already present. Thus, the E_{ea} of nitrogen is less favorable than that of carbon. Oxygen also must add an electron to an orbital that already has one electron, but the additional stabilizing effect of increased Z_{eff} across the periodic table counteracts the effect of electron repulsion, resulting in a more favorable E_{ea} for O than for N.
