Question

Why is the electron affinity of atomic nitrogen negative?

Answer 1

Perhaps we should examine the data first....

Explanation:

And I hope your eyes are better than mine cos I really need spex for this table.

We note (i) that the electron affinity measures the enthalpy of the following reaction....

`"Atom(g)"+e^(-)rarr"Anion(g)"^(-)+Delta`

And (ii), while the electron affinity generally increases across the Period from left to right as we face the Table (which we may attribute to increasing `Z`), the electron affinity of nitrogen as quoted is ENDOTHERMIC. This probably reflects Hund's rule of maximum multiplicity, which states the most stable electronic state is the one where electron spins are aligned. The nitrogen atom, in its ground state, has three unpaired electrons of parallel spin, and ionization (or reduction), will detract from this energetically favourable spin state.

And of course data, such as are provided in the Table, informed Hund's rule....