Nomenclature using prefixes

Multiplicative prefixes indicate the number of atoms of each element: mono-, di-, tri-, tetra-, penta-, hexa-, etc.

Examples:

• C₂H₂: dihydride dicarbon (a covalent compound — prefixes describe atom counts)
• AlH₃: aluminum trihydride (alane)
• LiH: lithium hydride
• CaH₂: calcium dihydride (calcium hydride)

Nomenclature by oxidation state

When hydrogen is more electronegative (as in hydracids) it is assigned +1; in metal hydrides hydrogen is commonly assigned -1. The oxidation state of the other element is indicated using Roman numerals or numbers in parentheses.

To determine the oxidation state, multiply the hydrogen charge (-1 in metal hydrides) by the number of hydrogens to obtain the total negative charge. That is balanced by the positive charge of the other element; divide by the number of atoms of that element to get its oxidation state.

Elements that typically have a single oxidation state (alkali metals +1, alkaline earth metals +2, aluminum +3) commonly omit the oxidation state in their names.

Examples:

• FeH₂: iron(II) hydride
• AlH₃: aluminum hydride (alane)
• LiH: lithium hydride

Nomenclature with suffix -ane

Hydrides of nonmetals that complete the valence shell can be named with the -ane suffix (analogous to organic -ane names).

Examples:

• CH₄: methane
• SiH₄: silane
• GeH₄: germane
• PH₃: phosphine (also called phosphane)

Hydracids (aqueous hydrides)

Hydrides of group 16 and 17 elements form acids when dissolved in water; these are called hydracids. Their aqueous state is indicated with (aq) or (ac).

Because the nonmetal is more electronegative than hydrogen, in these acids hydrogen is assigned +1 and appears at the beginning of the formula.

Names use the word "acid" followed by the nonmetal name with the suffix "-hydric" in many languages; in English we use e.g. "hydrochloric acid" for HCl(aq).

Examples:

• HCl(aq): hydrochloric acid
• HBr(aq): hydrobromic acid
• HI(aq): hydroiodic acid
• H₂S(aq): hydrosulfuric acid (hydrogen sulfide in water)

These substances are named differently in the gas phase:

• HCl(g): hydrogen chloride
• HBr(g): hydrogen bromide
• H₂S(g): hydrogen sulfide