# Hund's Rule for Determining Term Symbol Energy Order

Mr_Allod
Homework Statement:
Use Hund's rules to determine the energy order of the term symbols of a ##d^9f^1## electron configuration.
Relevant Equations:
None
Hello there, for the above question I have no issue finding the term symbols but I am a little unsure about employing Hund's rules to the electron configuration, particularly those referring to the energies based on the total angular momentum J. These state:

- In a less than ##\frac12##-filled subshell Lowest J-value is Lowest energy
- In a more than ##\frac12##-filled subshell Highest J-value is Lowest energy

For configurations where only one orbital is involved such as ##p^5,d^3## etc. this is easy to apply. But what about configurations where two orbitals are involved such as ##p^5d^1## or ##d^9f^1##? In these cases to which orbital do we apply the less/more than ##\frac 12##-filled condition?

Mentor
Hund's rules apply only to equivalent electrons. It would work for d9, but applying it to d9f1 is iffy.

In any case, considering that this is the problem you were given, the equivalent electrons being the d9, I would consider the subshell as more than half-filled.

Mr_Allod
Hund's rules apply only to equivalent electrons. It would work for d9, but applying it to d9f1 is iffy.

In any case, considering that this is the problem you were given, the equivalent electrons being the d9, I would consider the subshell as more than half-filled.
Thank you for the answer, I've had a very hard time finding a straight answer to this question anywhere so it's nice to have something to go on.