What is the oxidation number of hydrogen in CaH2?

In the compound calcium hydride (CaH2), the oxidation number of hydrogen is considered to be -1. This is because hydrogen typically has an oxidation state of +1 when bonded to nonmetals, but in this case, it is bonded to calcium, which is a metal. In ionic compounds formed between metals and hydrogen, hydrogen can exhibit a -1 oxidation state.

Calcium is an alkaline earth metal and typically has an oxidation state of +2. To maintain electrical neutrality in the compound, the two hydrogen atoms must collectively have an oxidation state of -2 (since +2 from calcium requires -2 from hydrogen). As there are two hydrogen atoms, each must therefore have an oxidation state of -1.

This context is important for understanding how oxidation states work in ionic compounds, especially when nonmetals are excluded from bonding relationships with hydrogen.