Q 2.67

[Haya Rabadi 1F]

Why for b) does it state that carbon has a higher electron affinity than nitrogen? Doesn't electron affinity increase across a period? Is this an exception to the rule?

[Michael Park]

This is an exception to the rule. Electron affinity is the energy it takes to add an electron to something. There are 2 electrons present in the 2p subshell in carbon's electron configuration, while there are 3 in the 2p shell for nitrogen. Because nitrogen's half filled electron shell is more stable than carbon's shell with only 2 electrons, carbon has a greater affinity for an electron when compared to nitrogen. Therefore, carbon has the higher electron affinity.

[KateCaldwell 1A]

Electron affinity increases going across (left to right) the rows and decreases go down columns. Carbon has a higher electron affinity than nitrogen due to its electron configuration. Carbon's electron configuration is 1s^2 2s^2 2p^2 and nitrogen's electron configuration is 12^2 2s^ 2p^3. Having two electrons fill the subshell is more stable than three electrons filling a subshell, so carbon has a higher electron affinity. There is a similar situation to the carbon and nitrogen situation which is silicon and phosphorus.