Excited State Electron Configurations:
So far we have only been talking about ground state electron configurations, when all of the
electrons are in their most stable, lowest energy configurations. You know that electrons can
also jump to an excited state if energy is added to them. What this means in terms of electron
configuration is that the sublevels are no longer filled in starting with the lowest energy and
going up. If an electron has jumped it can skip a sublevel or even an energy level. You should
be able to recognize an excited state electron configuration.
Let’s look at the energy level way of writing configurations first. For example, sodium in the
ground state is 2-8-1. One excited state configuration could be 2-7-2; on electron has jumped
from the second energy level to the third. The only rules to excited state configurations are that
they must contain the same total number of electrons as the ground state, and no energy level,
or sublevel can have more than its maximum number of electrons. I could not have written
1-9-1.
What is a possible excited state configuration for potassium if its ground state is 2-8-8-1?
Which of these is an excited state configuration?
2-8, 2-8-6, or 1-8-4
Let’s look at this in terms of the whole spdf configuration now. Write out the configuration of
neon:
1s22s22p63s1
A possible excited state might still have all of the energy levels
occupied, but maybe an electron jumped from the 2p sublevel to the 3s. Then you would have
1s22s22p53s2. Or maybe the 3s sublevel was skipped altogether and now you have 1s22s22p63p1.
Here are some problems to practice both ground and excited state electron configurations with.
One more thing to note is that there is a sort of short-hand notation that you can use when
writing out longer electron configurations. You know that every configuration starts out the
same – what you can do is abbreviate those first few energy levels by using the name as a group
18 element in brackets. For example, once you over neon, 1s22s22p6, you can abbreviate the
next element as [Ne]3s1, and so on, until you get to argon, when you can then use it as an
abbreviation. For example, calcium can be written as [Ar] 4s2. If you were to see a
configuration like this and wanted to figure out which element it was you would only have to
look at argon and count over two more.
Which elements are these?
[Kr] 5s24d2
Zr
[Ar] 4s23d10
Zn