# How do you use electronegativity values to determine the one element that always has a negative oxidation number when it appears in any binary compound?

So let's look at some simple compounds (or molecules) of fluorine: interhalogens, $F - X$; and $O {F}_{2}$. The oxidation states of the heteroatom are ${X}^{+ I}$ and ${O}^{+ I I}$, and of course we have ${F}^{- I}$. What is the oxidation number of fluorine in molecular fluorine, ${F}_{2}$?