Redox chemistry of elemental hydrogen
Elemental hydrogen (H2) can act as an oxidant (electron acceptor) or as a reductant (electron donor).
H2 acts as a reductant toward nonmetals.
The product is a binary compound containing H(+1) and the nonmetal in a negative oxidation state (The oxidation state is often Group Number - 18). The formula for the compound is such that the sum of the oxidation states is zero. For example, H2 reacts with
 reductant | +1 | H+ | oxidant  |
| 0 | H2 | ||
| -1 | H– |
The product is a binary compound containing H(+1) and the nonmetal in a negative oxidation state (The oxidation state is often Group Number - 18). The formula for the compound is such that the sum of the oxidation states is zero. For example, H2 reacts with
- N2 (Group 15) to give NH3 that contains N(-3) and H(+1)Usually the more positive element in a compound is given first in the formula. NH3 is an exception.
- O2 (Group 16) to give H2O that contains O(-2) and H(+1)
- Br2 (Group 17) to give HBr that contains Br(-1) and H(+1)
H2 acts as an oxidant toward metals.
The product is a binary compound containing H– and the metal in a positive oxidation state (corresponding to the last digit of its Group number). For example H2 reacts with:
- Li (Group 1) to give LiH containing Li+ and H–
- Ca (Group 2) to give CaH2 containing Ca2+ and H–