What is the proper name for CaH2?

The proper name for CaH2 is Calcium hydride because the compound consists of calcium (Ca) and hydrogen (H) in a 1:2 ratio. In this formula, "Ca" represents the calcium cation, which has a +2 charge, while "H" represents the hydride anion with a -1 charge. When naming ionic compounds, the cation is named first followed by the anion. Since hydrogen in this context is in the form of hydride, the name reflects this by using "hydride" instead of just "hydrogen."

In contrast, calcium oxide, calcium sulfate, and calcium carbonate involve different anions. Calcium oxide contains oxygen, calcium sulfate contains a sulfate ion (SO4^2-), and calcium carbonate includes a carbonate ion (CO3^2-). These specific anions lead to significantly different chemical properties and naming conventions, making them distinct from calcium hydride. Hence, the proper name for CaH2 is indeed Calcium hydride.