## S and d orbitals order in configuration

Julia Lindner 1I
Posts: 35
Joined: Fri Sep 28, 2018 12:17 am

### S and d orbitals order in configuration

I'm a little confused about the general rule for the order to fill in orbitals. Normally, is it correct to fill in the f and d-orbitals first (if there are any), then fill in the s and p orbitals? If you do this, the configuration tends to go in order of increasing n values (ex. 4f^14 5d^10 6s^2 6p^1). I know that there is some sort of exception with the order of 4s and 3d, but I don't understand when it applies since most of the configurations I've seen seem to fill 3d before 4s anyway.
My question is, is it usually safe to assume that the lower n values are filled first or are there many exceptions to this rule? Is there a better way to approach it?

Karina Koo 2H
Posts: 49
Joined: Fri Sep 28, 2018 12:24 am

### Re: S and d orbitals order in configuration

yup! I think youre on the right track that whatever has the lower n comes first, hence d usually ends up before s when its written out because of the fact that d is usually n-1 if the energy lv of s is n.

Aaron Ang 4H
Posts: 30
Joined: Fri Sep 28, 2018 12:28 am

### Re: S and d orbitals order in configuration

For all n values under 4, you could just fill them based on increasing n values and in the order of s-orbitals first and then p-orbitals. However, starting with an n value of 4, you would fill orbitals starting with the s-orbital followed by the d- orbital and then the p-orbital. However, when writing them down in the notation of electron configurations, you would write them in the order of increasing n value. For example, for Titanium with is in the 4th period, the electron configuration would be [Ar]3d^2 4s^2. The order in which you fill orbitals is different from the way in which you would write them.

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