Naming binary compounds

Binary compounds are compounds that consist of two elements. There are three types of binary compounds. Binary compounds containing:

1. two nonmetals (eg - CO)
2. metals with fixed ionic charges (eg - AgCl)
3. metals with variable ionic charges (eg - FeS)

In naming, each type of binary compound follows its set of rules.

Binary compounds containing two nonmetals

Rules for naming binary compounds containing two nonmetals:

1. Name the first element by its name.
2. The second element has the ending -ide.
3. The number of atoms of each element is indicated with Greek prefixes. In the case of mono-, it is only used for the second nonmetal. When no prefix appears, one atom is assumed.
4. If two vowels appear next to each other, the vowel from the Greek prefix is dropped. This is for ease of pronunciation.
   • monooxide becomes monoxide
   • tetraoxide becomes tetroxide
   • pentaoxide becomes pentoxide

Examples

CO - carbon monoxide

CO₂ - carbon dioxide

CCl₄ - carbon tetrachloride

SO₂ - sulfur dioxide

N₂O₄ - dinitrogen tetroxide

Binary compounds containing metals with fixed ionic charges

Thirteen metals on the periodic table have fixed charges.

Group	Metal	Fixed charge
Group IA	Lithium, Li	+1
	Sodium, Na
	Potassium, K
	Rubidium, Rb
	Cesium, Cs
Group IIA	Magnesium, Mg	+2
	Calcium, Ca
	Strontium, Sr
	Barium, Ba
Group IIIA	Aluminum, Al	+3
Group B	Zinc, Zn	+2
	Cadmium, Cd	+2
	Silver, Ag	+1

Rules for naming binary compounds containing metals with fixed ionic charges:

1. Name the metal first followed by the nonmetal with the ending -ide.
2. No Greek prefixes necessary here because the metal has a fixed charge and, therefore, in forming a compound, there is only one possible combination with the nonmetal.

Examples

KCl - potassium chloride

CaH₂ - calcium hydride

Al₂S₃ - aluminum sulfide

ZnCl₂ - zinc chloride

Binary compounds containing metals with variable ionic charges

Many metals on the periodic table have variable charges. For example, the element iron, Fe, can occur as +2 ions in some compounds and can occur as +3 ions in other compounds. When naming compounds involving metals with variable charges, the charge associated with the metal cations in the compound needs to be determined.

Rules for naming binary compounds containing metals with variable ionic charges:

1. Determine the charge of the metal in the compound.
2. Name the metal followed by a Roman numeral in parentheses immediately following the name of the metal. The Roman numeral represents the charge of the metal.
3. Name the nonmetal with the ending -ide.
4. No Greek prefixes necessary here because the charge on the metal is labelled, therefore, in forming a compound, there is only one possible combination with the nonmetal.

There are five common metal ions with variable charges that are named using their Latin stem. Learning the Latin names will help in figuring out the charge on the metal ions.

Metal	Cation	Latin Name
Copper, Cu	Cu+	Cuprous ion
	Cu2+	Cupric ion
Iron, Fe	Fe2+	Ferrous ion
	Fe3+	Ferric ion
Lead, Pb	Pb2+	Plumbous ion
	Pb4+	Plumbic ion
Mercury, Hg	Hg22+	Mercurous ion
	Hg2+	Mercuric ion
Tin, Sn	Sn2+	stannous ion
	Sn4+	Stannic ion

Examples

CuS - copper (II) sulfide or cupric sulfide

SnF₄ - tin (IV) fluoride or stannic fluoride

Fe₂O₃ - iron (III) oxide or ferric oxide

PbCl₂ - lead (II) chloride or plumbous chloride

Content suitability

BCIT courses: CHEM 0011