Question

What occurs when an electron is added to an atom?

Answer 1

You have got a reductive rather than an oxidative process..

Explanation:

When an atom is REDUCED an electron has been added to its valence electron shell. And so, for chlorine...

`Cl(g) + e^(-) rarr Cl^(-)(g)`

Of course we know that chlorine, like most elemental gases, is binuclear, but clearly we can perform the given reaction by some means. The chloride anion SHOULD be substantially larger than the parent atom inasmuch as while `Z`, the nuclear charge, remains constant, the electron-electron repulsion should INCREASE. Capisce?

The thermodynamics of the given reaction is reported in tables of `"electron affinity"`?

On the other hand, when potassium metal is oxidized it loses that valence electron whose orbit reasonably defines the atomic radius. With me?

`K(g) +Delta rarr K^(+)(g) + e^(-)`

As chemists, as physical scientists, we should seek actual data that inform our reasoning; see this site.