Chemistry problem

[Dr.9999]

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The electronic configuration of a particular neutral atom is 1s2, 2s2, 2p6, 3s2, 3p1. The number of unpaired electrons is?

Why is the answer 1?
I thought 3p1 is Al and therefore it would be 3 unpaired electrons not 1.

 

[FeralisExtremum]

You're looking at this the wrong way, from the perspective of valence electrons, rather than paired spins. Al has 3 valence electrons, yes - but 2 of those valence electrons are paired with each other (they have opposite spins) in the s orbital. There is only electron in the p subshell with no other electron paired with it.

Another example: Neutral P has a configuration of 1s2, 2s2, 2p6, 3s2, 3p3. It has 3 unpaired electrons.

Another: Neutral S has a configuration of 1s2, 2s2, 2p6, 3s2, 3p4. It has 2 unpaired electrons.

Remember Hund's rule! The "pairing" refers to filled (paired) vs half-filled (unpaired) electrons.

 

[Dr.9999]

I totally understand the neutral P, and the S example you gave me. What I did is I made 3 box for the P orbital and starting filling in the electrons according to Hunds rule. However for Al there is only one electron in one of the three boxes I drew for the P orbital so why is there 1 unpaired? Is it b/c the other two boxes are empty and so you only count the box that has the Al electron? I hope I make sense lol...

Thanks

 

[FeralisExtremum]

Yes, exactly what you said - since the other two boxes are empty, there's no electrons in there to be considered paired or unpaired. Only the single box that has an electron.