# How many electron levels exist?

May 15, 2018

As many as the atom needs.

In reality, electron energy levels are "accessed" as soon as the electron "occupies" an orbital in a new energy level. Energy levels of empty orbitals don't really exist. We just like to say they do for simplicity, and draw, e.g.

$\underline{\uparrow \downarrow}$

for a $1 s$ energy level "occupied" by two electrons.

The usual orbitals atoms have often used (grouped by angular momenta) are:

$1 s , 2 s , 3 s , 4 s , 5 s , 6 s , 7 s$
$2 p , 3 p , 4 p , 5 p , 6 p , 7 p$
$3 d , 4 d , 5 d , 6 d$
$4 f , 5 f$

No atom has so far used a $5 g$ orbital yet, so they do not exist yet. They're not there until they're needed. If we ever get to element number $121$, we might have a chance of seeing a $5 g$ orbital being used, but since those are so radially compact and have 4 angular nodes, we might need to wait even longer than that...