Help with Electron-configuration

  • Thread starter abotiz
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  • #1
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Main Question or Discussion Point

Hi

Iam having a little problem understaning why some atoms are configured in a certain way.

I know that each sub-shell can take 2(2l+1) electrons, so for
s->2
p->6
d->10

But why e.g does the atom, Cr (Z=24) have the configuration : ...3d54s1 rather than ...3d6 ?

I know about that electrons in d sub-shell has higher energy than s and p, ( s<p<d )

Is this something we just have to accept because we know from experiments that Cr has the total energy X, so it cant possibly have ...3d6?

Or is there some other explanation?

Thanks!
 
Last edited:

Answers and Replies

  • #2
611
2
Please refer to Pauli rule and also hund's rule..[however one rule is usually applied in electronic configuratiions]
you will get the answer.
 
  • #3
SpectraCat
Science Advisor
1,395
1
Hi

Iam having a little problem understaning why some atoms are configured in a certain way.

I know that each sub-shell can take 2(2l+1) electrons, so for
s->2
p->6
d->10

But why e.g does the atom, Cr (Z=24) have the configuration : ...3d54s1 rather than ...3d6 ?

I know about that electrons in d sub-shell has higher energy than s and p, ( s<p<d )

Is this something we just have to accept because we know from experiments that Cr has the total energy X, so it cant possibly have ...3d6?

Or is there some other explanation?

Thanks!
Yes, this is from experiment. It is known that full and half-full angular momentum sub-shells show anomalous stabilities. It is best known for the transition metals, where the atoms with s2d4 configurations spontaneously promote to s1d5 configurations ... the latter configurations are the observed ground states in nature. Half-filled p-shells (i.e. p3) are also anomalously stable, as can be seen from the details of the trends in the experimental ionization energies of the elements.

You might want to google "periodic trends", or read about them in your textbook, for more information.

@ moderator: This thread probably belongs in the chemistry forum.
 
  • #4
72
0
Thanks for the quick replies!

Also, Thank you SpectraCat for clearing that up for me =)
 

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