Oxidation number of Metals

[almaortega]

I know that oxidation number is the hypothetical charge of the element if it were fully ionic (made all bonds it could), but how would you calculate it for metals? I noticed Co is +3 and Ni is +2, why are they not -3 and -2 since adding 3 or 2 more electrons (making it negative) would complete the 3d orbital?

[zackdouchy]

The reason that metals do not form negative charges is solely based upon periodic trends. Metals tend to form cations because they have a low ionization energy and therefor will not require much energy to remove an electron from its outer shell. Additionally, metals do not form anions because they have a low electron affinity. Meanwhile, nonmetals tend to form anions because they have a very high ionization energy and a high electron affinity to form anions. Hope this helps!

[LouiseLin2L]

Metals tend to lose electrons to gain stability, which is why their oxidation number would be positive.

[Eric Sun 2G]

Based on the periodic trends, metals are more likely to give away electrons and become cations with a positive charge. It is very rare that metals would have an oxidation state that is negative as a result.

[carterwink2K]

I think that unpaired electrons within orbitals play a role in making the metals want to give away electrons. Some metals fill up their d orbital already, as they lose the s orbital electrons because of the higher energy level.