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I'm trying to understand why ChemReference sometimes lists the valence electrons as a number I don't expect. Take oxygen, for instance. It should have six valence electrons, however the site lists two. Why?

I hear that, for transition metals, the d-orbitals count towards the valence. Is there another rule like that I need to know about that might explain Oxygen?

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    $\begingroup$ I suspect software bug might be the answer here. I can't think of any definition of valence electrons (there are some different takes on the concept, but not for light elements) by which Oxygen would have 2 valence electrons, let alone how it could have 2 and Nitrogen would still have 5. But perhaps there is a definition by which it makes sense. $\endgroup$
    – user7652
    Commented Nov 18, 2015 at 2:54
  • $\begingroup$ I just saw a bug report in which he refers to those valance as the "common valence". Never heard of that before. Have you? $\endgroup$
    – mdeforge
    Commented Nov 18, 2015 at 4:25
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    $\begingroup$ I have not. It seems this is what he is referring to: en.wikipedia.org/wiki/Valence_%28chemistry%29#Common_valences . That's pretty obscure terminology, and I'm not sure how it relates to the values being given. Perhaps what he's getting at is the common number of bonds formed by the element. That wouldn't make sense for N, though. $\endgroup$
    – user7652
    Commented Nov 18, 2015 at 4:33

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Look closely on that site. It's not 'valence electrons' but 'valence'. There is a difference between the valence electrons and valence.

Valence electrons are the number of free electrons in an atom that can take part in making the bond. There are 6 such electrons in the oxygen atom as you stated.

While the valence or valency is the number of bonds that can be made by the atom.

That's why valency of oxygen is 2

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  • $\begingroup$ Interesting. Why aren't those numbers the same? If there are six electrons in a valence shell, aren't all six free to make bonds? $\endgroup$
    – mdeforge
    Commented Nov 18, 2015 at 17:05
  • $\begingroup$ there is also the octet problem if all those 6 electrons participate in the bond formation. A neutral oxygen atom needs 2 electrons to complete its octet and he get it by making two bonds. $\endgroup$
    – manshu
    Commented Nov 18, 2015 at 17:08
  • $\begingroup$ So the way to calculate it would be to take the number of valence electrons an element has and then figure out which is less... adding electrons to get to 8, or subtracting electrons to get to 8, and then that number is the valence? $\endgroup$
    – mdeforge
    Commented Nov 19, 2015 at 3:35
  • $\begingroup$ @Stradigos Yes but it only works until the octet rule is followed. $\endgroup$
    – manshu
    Commented Nov 19, 2015 at 7:54

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