Californium (Cf) electron configuration

[yui_96]

How does the element Cf have electron configuration 5f10, 7s2? Why is it not 5f9 as its position on the periodic table shown?

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[JustinM88]

http://schoolbag.info/chemistry/mcat/mcat.files/image289.jpg

AHHHH I think I found your problem...compare the following periodic table to the first one I linked lol:
http://1.bp.blogspot.com/_k_0hECgG5.../w1200-h630-p-k-no-nu/MCAT+Periodic+Table.png

 

[Lawpy]

How does the element Cf have electron configuration 5f10, 7s2? Why is it not 5f9 as its position on the periodic table shown?

s orbitals hold 2 electrons
p orbitals hold 6 electrons
d orbitals hold 10 electrons
f orbitals hold 14 electrons

Orbitals are most stable if they are half filled or completely filled by electrons. So f orbitals are most stable if they have 7 or 14 electrons.

Californium has electron configuration of [Rn] 7s2 5f10 because the f orbitals are neither half filled nor completely filled. However, for curium, it's incorrect to say the electron configuration is [Rn] 7s2 5f8 because one of the f electrons would go down to the next lower orbital to be more stable. This means the 5f orbital would go to a 6d orbital to have the stable electron configuration of [Rn] 7s2 6d1 5f7.

I just want to point out that comparing energy levels between d and f orbitals becomes complicated and is beyond the scope of the MCAT, unless it's specifically stated in a passage. You usually compare between d and s or p orbitals.

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EDIT: if you want to see why comparing d and f orbitals becomes complicated, take a look at the following electron configurations:

You can see for certain elements that there is a weird exchange of electrons between d and f orbitals... for reasons beyond the scope of the MCAT.

Lathanides have a similar behavior. For more information, see: Lanthanides: Properties and Reactions

 

[yui_96]

AHHHH I think I found your problem...compare the following periodic table to the first one I linked lol:

Yes! This is exactly I was thrown off because of the different arrangement of the periodic table. Thank you so much for helping me figuring out my problem!

 

[yui_96]

s orbitals hold 2 electrons
p orbitals hold 6 electrons
d orbitals hold 10 electrons
f orbitals hold 14 electrons

Thank you for your thorough explanation. Now I can totally see the difference between Cf and Cm!