TBR Chapter 2 Chem Question

[Machine33]

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Why is the second ionization energy for Mo greater than that of Tc? Ionization energy increases from left to right with the exception that if it was ionized the first time and then is on a 5th or 10th orbital, than the energy will be higher than the first but Mo is at D-3 where Tc would be at D-4 after the first ionization. What do you guys think?

 

[mcloaf]

Because as you ionize Tc, you're losing electrons from the S shell, not the D. So you lose the two outer S electrons and still have half full D shell stability.

In Mo one of the electrons from the S shell has already moved into the D shell to give you half filled stability. This means you can only lose one outer electron from Mo before you have to overcome half shell stability.

 

[MedPR]

Because as you ionize Tc, you're losing electrons from the S shell, not the D. So you lose the two outer S electrons and still have half full D shell stability.

In Mo one of the electrons from the S shell has already moved into the D shell to give you half filled stability. This means you can only lose one outer electron from Mo before you have to overcome half shell stability.

This is correct.

Elemental Mo is 5s1 4d5, not 5s2 4d4.
Elemental Tc is 5s2 4d5