Question G CHEM !!! HELP!

[FutureDental88]

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Im a little confused..

I was doing a problem on destroyer asking " how many unpaired electrons are there in Mo" (Molybdenum".
Mo has an atomic number of 42 (4s2 3d4). And due to the transfer of one electron from its S to D orbital. It becomes 4s1 3d5. Giving it according to destroyer 6 LONE PAIRS.


However: I was doing a similar problem on ADA sample test where they asked how many unpaired electrons a neutral atom 1s2 2s2 2p6 3s2 3p2 have ?.
Same here: Due to transfer of 1 e from 3s orbital to 3p. It should become 3s1 3p3. giving it a total of 4 Lone pairs i thought but the answer says 3 lone pairs.



WHICH ONE IS CORRECT???? Seems like destroyer is counting the lone pair in the S orbital. While ADA sample is not.

 

[herkulease]

Destroyer is correct. Mo and few others are exceptions to the how to fill up the shells.

in the ADA case. there is only 2 unpaired electrons. for some reason that questions # 67 is the lone misprint. I have a printout before they redesigned the website it had the correct choice of B.

Anyhow unless it is one of those elements that is an exception or in an electron configuration that is provided and they promote an electron up you should not promote any electrons yourself. Take what is given and determine the answer.

 

[FutureDental88]

Well.. if destroyer is right, then ADA should be 4 lone pairs on question 67. And not 3. And not 2 as your saying.

Because 1 electron from the S shell is transferred to the P shell to stabilize it. Giving it 4 lone pairs if taking account for the P+S orbitals

 

[herkulease]

Well.. if destroyer is right, then ADA should be 4 lone pairs on question 67. And not 3. And not 2 as your saying.

Because 1 electron from the S shell is transferred to the P shell to stabilize it. Giving it 4 lone pairs if taking account for the P+S orbitals

I think you're reading the question wrong.

It is asking for UNPAIRED electrons. Not Lone pairs. Lone pairs are something entirely different and has nothing to do with electron configuration. It is something that is an issue when it comes to lewis structure or in terms of bonding.

Cr, Mo, Cu, Au, and Ag are the exceptions, they are the ONLY ones in which you should be doing any promoting of electrons(on your own) to have half filled shells.

This is why you have 6 unpaired electrons.
5s1 <-- 1 unpaired electron
4d5. <-- 5 unpaired electrons

In the Ada problem. they provide you with the electron config of Silicon. It is in a neutral state. It has NOT been excited and it is NOT one of the exceptions mentioned. Therefore do NOT promote the electrons yourself.

3s2 <-- 0 unpaired electron.
3p2 <-- 2 unpaired electrons.

 

[FutureDental88]

Ok. Got it !! Thanks a lot for your thoroughness