[alexmahone]

In other words, why is the anion formed usually more stable than the neutral atom plus the electron?

[mugabo daniel]

ENERGY MUST BE SUPPLIED TO ATTACH AN ELECTRON

[Dan]

ENERGY MUST BE SUPPLIED TO ATTACH AN ELECTRON

1. Do not type in all caps.
2. Completely incorrect.

Energy must always be supplied to remove an electron. Consider the energy level diagram for an atom, e.g.:



You can see that no matter which orbital an electron resides in, it is always lower in energy than the free electron. The basic reason behind this is that the nucleus stabilises electrons by a favourable Coulombic interaction (+ attracts -).

[mugabo daniel]

thanks Dan but i thought energy has to be supplied to overcome the repulsion from the orbital electrons.

[Dan]

For the first electron affinity, where an electron is added to a neutral atom, the attraction from the nucleus overcomes the the repulsion from the other electrons.

Subsequent electron affinities are often negative because now this process involves adding an electron to an anion, and electronic repulsion often overcomes nuclear attraction.