Introduction to Binary Compounds

Oxides and hydrides are usually studied separately, but there are many more elements that can form binary compounds. The most electronegative element is named with the suffix -ide. In other traditional names, elements like sulfur (S) are named as sulfide.

Nomenclature by prefixes

Prefixes that indicate the number of atoms of each element are used: mono-, di-, tri-, tetra-, penta-, hexa-, etc.

Examples:

• CaI₂: calcium diiodide
• CO₂: carbon dioxide
• SF₆: sulfur hexafluoride
• PCl₅: phosphorus pentachloride

Nomenclature by oxidation state

In this case, the oxidation state of the metallic element or the most electropositive element is indicated using Roman numerals or its charge in parentheses.

To determine the oxidation state, it is considered that the most electronegative element has a fixed charge according to its distance to noble gases. For example, -1 (F, Cl, I, ...), -2 (O, S, Se, ...), -3 (N, P, ...), -4 (C, ...).

The charge of the less electronegative element is calculated so that it compensates for the charge of the more electronegative element.

The oxidation state of elements that usually only have one of them is not indicated, such as alkali metals (+1) (Li, Na, K, ...), alkaline earth metals (+2) (Be, Mg, Ca, ...), or aluminum (+3).

Examples of nomenclature by oxidation state:

• CaI₂: iodide of calcium (no oxidation state indicated)
• NaCl: chloride sodium (no oxidation state indicated)
• FeCl₂: chloride iron(II)
• FeCl₃: chloride iron(III)
• PbS₂: disulfide lead(IV)