Why is the oxidation state of oxygen in nitrite not #-4#?
Here's what's going on here.
You may be confusing oxygen's oxidation state with its total oxidation state contribution. For oxygen in
You're dealing with the nitrite anion,
Now, oxidation numbers are assigned by taking into account the electronegativity of the atoms that form a covalent bond.
More specifically, you assign oxidation numbers by assuming that the more electronegative atom "takes" the bonding electrons shared to form the covalent bond.
In most covalent compounds, oxygen has an oxidation state of
Now, it's very important to realize that oxidation numbers are assigned per atom. Since you have
#ON_"nitrogen" + 2 xx ON_"oxygen" = -1#
You know that oxygen has an oxidation state of
#ON_"nitrogen" + stackrel(-4)overbrace(2 xx (color(blue)(-2))) = -1#
This will of course result in a
Therefore, the oxidation states of nitrogen and oxygen in the nitrite anion are