I'm confused about something. If there are an infinite number of energy levels available to an atom, how and why would an ionization need to take place? The electron always has another energy level to occupy once its energy has been raised.
1 Firstly note that that an infinite number of energy levels does not mean an infinite energy, there is a maximum energy the electrons in an atom can have and you have maybe seen a picture of a spectrum where the lines get closer and closer going up to this maximum; it is quite analogous to escape energy in classical.
2 Secondly anyway they don't escape to infinity of eempty space like a rocket escaping earth gravity - they go somewhere else where they can have less energy creating a 'counter ion', assisted also in aqueous solution by water molecules orienting their charges oppositely to stabilize the ion.