Pauli Exclusion Principle
From quantum rules, electrons don�t like to be packed into a small
space, either in atoms or in ionized gas
At normal ionized gas densities, electrons are so spread out
quantum rules don�t matter.
As high enough ionized gas densities, quantum rules need to be
considered, just has they have been in atoms
Think of each �atom sized� region of space having a set of energy
levels associated with it(although it is really more complicated)