ACS Gen Chem Question

[GiTsticker]

Advertisement - Members don't see this ad

An atom has two 4s electrons and six 3d electrons. How many unpaired electrons would there be in the Fe2+ ion?

a) one b) two c) three d) four

Book says D, four. That would mean the electrons from the d orbital would be lost first. I would think that one would be taken from the d orbital and then the other from the s orbital so that both the s and d orbitals would be half full. Someone please clarify.

Thanks.

 

[grayzkule]

Having "half full" orbitals doesn't help anything and therefore it wouldn't tend towards that direction. The two electrons lost are both electrons from the S orbital because the 4S orbital is higher energy than the 3D orbital. The question is asking how many electrons are unpaired (i.e. number of orbitals with only one electron).

This is normal Fe
D orbitals: _u,d_ _u_ _u_ _u_ _u_
S orbital: _u,d_

For Fe2+ it is:
D orbitals: _u,d_ _u_ _u_ _u_ _u_ (the exact same thing)
S orbital: __ (empty)

The first D orbital has both up and down spinning electrons, but the other four only have the up. The S orbital is empty. Therefore, only 4 electrons in four of the D orbitals are unpaired.