1s
2
2s
1
Lithium has 2 electrons in the s-orbital of the 1st energy level and 1 electron in the s-orbital of its second
energy level.
This brings up a point about which orbitals are allowed in a particular energy level.
Each energy level can
have the following orbital values (which you should be able to see why from the quantum numbers listed
earlier)
n = 1
s
n = 2
s, p
n = 3
s, p, d
n = 4
s, p, d, f
n = 5
s, p, d, f, g
Each new energy level builds one more new orbital from the previous one.
To complicate matters even further, in a many electron atom, because of the interaction between the
electrons (the
shielding effect
) and the nucleus (
effective nuclear charge Z
*
), the energy levels overlap
one another in such a way that the increase in energy for those atoms are:
1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p
Note that even though the 3d sublevel is higher in energy than the 4s, when writing spectroscopic
notation, energy levels are grouped together by n number, not by the increase in energy.
As an example
of this Arsenic (As) would be written as 1s
2
2s
2
2p
6
3s
2
3p
6
3d
10
4s
2
4p
3
instead of 1s
2
2s
2
2p
6
3s
2
3p
6
4s
2
3d
10
4p
3
Condensed Spectroscopic Notation
Another way to represent the electron configuration of an atom is called
condensed spectroscopic
notation
.