[Bridget Jones]

When determining the oxidation number of a specified element what are the steps? Please don't refer me to other chemistry web-sites because I have tried and they still don't clarify what i need to know. Perhaps I am over complicating things! eg when determining the oxidation number of N in NF3 I understand the ON of N is -3 and that F is -1. Is that enough? Another example is determine the oxidation number of P in P2O5 - again the ON of P is-3 and O is -2 but I don't know what to do next - perhaps I don't need to do anything else?

I have searched the forums for help but still can't find what I am looking for. To all you chemistry whizzes out there, try and be a little more tolerant. On reading some answers I get the impression that some of you think we students must be brain dead if we don't understand it - we all have strengths in different areas!!!

Many thanks.

[UG]

Hi Bridget Jones,
The sum of the oxidation numbers of any neutral compound must be equal to zero. For NF₃: the O.N of fluorine is always -1 for any compound, so the O.N of nitrogen is +3, i.e 3 x -1 + 3 = 0   easy peasy right?
For polyatomic ions, the sum of the oxidation numbers equals the charge of the ion, for example SO₄^2-, O.N of oxygen is always -2, except in peroxides where it is -1, so... you have -8 + O.N(S) = -2 therefore the oxidation number of sulfur is +6 in this ion. I think now you can work out the oxidation numbers for P₂O₅.

[CCG]

i've been stuggling with oxidation numbers myself lately.  the examples above really hepled me understand the basic concepts.  i still don't quite understand how to apply the 'rules' to compounds with "( )".  for example, how do i determine the oxidation number of Cr in Cr(OH)₃?   i'm not sure of any of this but this is my train of thought:  compound is neutral so i'm looking for o.n.'s that will add up to zero.  OH (or OH-) is -1.  -1 x 3 = -3.  so Cr = +3?  thanks for the *delete me*

[UG]

Yep, Cr is in the +3 oxidation state, you're right on the money 

[woodiermonkey]

hey, i am not sure how to work out the oxidation state, coordination number and d electron configuration for these. These are practice questions that i got on a worksheet but i cannot find the answers anywhere. any help would be great, thanks 

Mn7+
Ag+
[Co(NH3)6]3+
[Co(NH3)6](NO3)3
[Pd(NH3)4(H2O)2]SO4
Na2[Cr(CN)6]
[NH4][Co(en)I4]
[Cr(en)2Cl2]Cl
[Fe(CO)5]
cis-[PtCl2(NH3)2]