[dnice8705]

  ???How do you find oxidation numbers on molecules? SUch as:
N2H4

Shouldnt i find how many Electrons needed, then find the number of bonds, then subtract electron pairs from valence electrons...to come up with -2?

[Alberto_Kravina]

It's not really easy to determine the ox-num of elements, but I hope that this helps:

Draw the structure of the molecule and put all bonding electron pairs to the most electronegative atom.

e.g.   O=C=O   => O is more electronegative
      __                      __
=> |O|     +   C    +    |O|
       ^{__                       __}

Oxygen has 6 electrons in it's elementar state, in this case the oxygen atom has 8 electrons (2 electrons more), so it has the oxidation number -2 (an electron has a negative charge). You have to compare the number of electrons in the elementar state and the number of electrons in the molecule (after putting the bonding electrons to the more electronegative atom).

Carbon has 4 electrons in it's elementar state, in this case no electron is associated to carbon => 4 electrons are missing => ox-num is +4

Hint: The most common ox-num for Oxygen is -2 (except in peroxides, hyperoxides and OF₂) and Hydrogen has always the ox-num +1 (excpt in metal hydrides)

I hope that you understand my explanation....

[Borek]

How do you find oxidation numbers on molecules? SUch as:
N2H4

Problem with oxidation numbers is that it is not well defined, measurable property of atom in molecule. Sometimes it is hard to assing ON to atoms, sometimes it can be done in more than one way and there is no way to check which ON assignement is correct.

[dnice8705]

both of your responses greatly helped me...really im (re)learning redox reactions in CH101. I took chemistry and did very well in high school, only problem is, in high school you got a lot of credit for just doing your homework, and in high school you took a test on a single chapter, so you got to study and focus on one chapter at a time, which left very little space/time for confusion. In college you get graded on 4 exams, and you have to take them on a wide variety of subjects within that subject...in short...COLLEGE SUCKS!

[Borek]

In college you get graded on 4 exams, and you have to take them on a wide variety of subjects within that subject...in short...COLLEGE SUCKS!

If so, LIFE SUCKS too. You have to deal with everything at the same time.