Confusing!

[ChemSiddiqui]

Hi all,

 

I was asked this question which made me 2 think a lot. I will share it with you and want your take on it.

 

" Zinc and Copper are d-block elements with atomic radius measured in nanometres are 0.125 and 0.117 repectively. The data booklet I have got says that the first ionisation energy of zinc is +908 KJ/mol while copper's is +745 KJ/mol. Question is why zinc has a higher ionsation energy than copper when it size is larger than of cooper(slightly at least)"

 

So what I have got for answer was this:

 

Zn = [Ar] 3d10 4s2

 

Cu = [Ar] 3d10 4s1

 

Zn and Cu both have their valence electron in 4th shell and they are sheilded by equal no of electron in both cases. We know that atomic radius decreases across the period because of the increase in the nuclear charge and no sheilding effect(not very effective i mean). One reason I see for higher ionisation energy of zinc is that its nuclear charge is more positive due to increase in the number of protons. But I fail to understand why zinc atomic radius is larger than copper. 2 questions:

 

1. Is the question right ( i mean does it make sense)?

 

2. Your comments on my reasoning above.

 

Any help most appreciated:-) .

[Testo]

Zn has a full 4s orbital, Cu has an unpaired electron in the 4s - the reason for why Zn has a higher ionisation energy is due to the pairing energy difference i.e. you need to put in more energy to unpair an electron (also compare Ag with Cd and Au with Hg). But as to why the radius is larger I don't really know...