How is ionization an endothermic reaction?

[dolimitless]

I don't get how ionization is an endothermic reaction.

In an endothermic Reactions: the reactants have less potential energy than do the products. Energy must be input in order to raise the particles up to the higher energy level.

The ionization energy, is the energy required to completely remove a valence electron from a gaseous atom or ion.

EX: Na(g) → Na+(g) + e- I1 = 496 kJ/mole

The reactant though, Na, has more potential energy (it is further away from the nucleus when compared to its ionic counterpart, which just lost an electron) than the product?

Am I thinking wrong? PlEASE HELP!

 

[Glenn Rudge]

Ionization is a two way process, what I'm saying is ionization occurs when the atom body has too little electrons or too many.

 

[Bob S]

Ionization of a material (gas, liquid, or solid) by a high energy charged particle is a collision between the fast charged particle and an electron bound in a stationary neutral atom. The electron is ejected from the atom, leaving an atom missing one electron. This is the basis for the Bethe-Bloch equation. The minimum energy transfer is of the order of the ionization. Energy must be input to leave the atom in an excited (ionized) state, so it is endothermic..
See http://en.wikipedia.org/wiki/Bethe_formula