Valency of Copper


by Sam Morse
Tags: copper, valency
Sam Morse
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#1
Jan11-13, 05:12 AM
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Writing the electronic configuration of Cu :

[Ar] 4s13d10, I feel that the number of valence electrons in a copper atom is 11. But it doesn't make any sense to me why copper has a valence of 1 or 2 as in case of CuSO4 .... which is 2.

Going the usual way, if we consider Sodium, which has an atomic number of 11, we find that it's electronic configuration is [Ne]3s1 and it's very clear why it has a valency of 1. But why doesn't copper go that way ?

Thanks for any help.
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Borek
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#2
Jan11-13, 05:53 AM
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Take a look at the periodic table - is it 4s13d10, or 4s23d9? Energy difference between both is small, so it is hard to say if there is 1 or 2 valence electrons (4s) - and copper itself can't decide, sometimes being +1 and sometimes +2
DrDu
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Jan11-13, 07:14 AM
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You also have to take in mind that metals seldomly form covalent bonds whence it is not appropriate to speak of valency of copper.
In CuSO4 it makes more sense to speak of an oxidation number of +II. Higher oxidation numbers are generally less and less stable as it costs more and more energy to remove another electron from an already positively charged ion.
Additionally in Cu and Zn, the d-electrons are already very tightly bound as d-electrons are not very efficient in screening each other from the nuclear charge.

Sam Morse
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#4
Jan11-13, 07:50 AM
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Valency of Copper


Basically, I want to know how do I find the valency of copper by writing the electronic configuration like I wrote for Sodium. [Ne]3s1. Here, I find that sodium's valency is 1 which is in 3s1. But how do I do the same for copper ?
Pranav-Arora
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#5
Jan11-13, 09:31 AM
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Quote Quote by Sam Morse View Post
Basically, I want to know how do I find the valency of copper by writing the electronic configuration like I wrote for Sodium. [Ne]3s1. Here, I find that sodium's valency is 1 which is in 3s1. But how do I do the same for copper ?
Transition elements show variable oxidation states due to which its difficult to find the valency of them by simply writing their electronic configuration. For example, take Manganese, it shows oxidation states ranging from +2 to +7 but only some of them are found commonly.
Sam Morse
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#6
Jan11-13, 10:00 AM
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So, what shall I do in such a critical situation. Memorise ?
Borek
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#7
Jan11-13, 11:33 AM
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That would work.
Pranav-Arora
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Jan12-13, 08:15 AM
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Quote Quote by Sam Morse View Post
So, what shall I do in such a critical situation. Memorise ?
Yes, you have no other choice.
Sam Morse
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#9
Jan13-13, 02:19 AM
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OK ... I will memorise. Thanks everybody ...
epenguin
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#10
Jan14-13, 05:35 AM
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Well not quite IMHO.
Make the memorising involve connecting up with as many significant and hopefully interesting other things as possible.

In Chemistry (and transition metal chemistry particularly) we are lucky to have a lot of colours and other visible things to provide mental hooks. Hopefully you see some of the substances and reaction in a lab and not just in a book.

The colour of cupric salts/ions is one of the first and most striking and memorable met in chemistry. I did not know till a minute ago that "copper sulphate is one of the few substances which shows the same absorption spectrum in the solid sate and in solution"!

Connect the colours and oxidation states with Fehlings test which is another piece of semi-elementary chemistry you learn maybe later. Useful.
If your interests are likely to be in biology, copper and its oxidation states are of quite some importance, the enzyme cytochrome c oxidase via which you could be said to breathe and live, involves cycling between Cu+ and Cu2+ in part of what is I'm afraid a fairly complicated story.
Or you could look at the quantum mechanical rationale of the states of copper, relative stability, ease of oxidation/reduction, coours etc. someone here might help about.
If interested in minerals there is a lot of colourful stuff.
There are connections to archaeology and history.

These are maybe counsels of perfection depending on your ambitions for the future, might be useful to some other reader. Always connect a.f.a.p. anyway if you want to get on top of the mass of stuff to learn instead of it on top of you. Try run before walk whenever you can. Not everybody will agree. At least I learned one thing today!


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