Assigning Oxidation Numbers

Vocabulary flashcards outlining the general rules for assigning oxidation numbers to elements, monatomic ions, polyatomic ions, and specific compounds containing hydrogen, fluorine, and oxygen.

Oxidation number of a 'free' element

Equal to $0$ for any element by itself (e.g., $Zn$, $O_2$, $Mg$, $Na$, $I_2$, $S_8$, $P_4$).

Oxidation number in simple (monatomic) ions

Equal to the charge on the ion (for example, in $MgCl_2$, the oxidation number is $-1$ for $Cl^-$ and $+2$ for $Mg^{2+}$).

Oxidation number sum rule for molecules and polyatomic ions

The sum of the oxidation numbers for all atoms equals the overall charge on the molecule or ion.

Oxidation number of Hydrogen ($H$)

Equal to $+1$ when bonded to nonmetals (such as in $CH_4$) and $-1$ when bonded to metals (such as in $CaH_2$).

Oxidation number of Fluorine ($F$)

Equal to $-1$ in compounds with all other elements.

Oxidation number of Oxygen ($O$)

Equal to $-2$.