What Is a Binary Compound? Definition and Examples

Binary Compounds
A binary compound consists of two different elements.

In chemistry, a binary compound is a chemical compound consisting of exactly two different elements. Although a binary compound only contains two elements, it can contain more than two atoms. The three types of binary compounds are binary acids, binary ionic compounds, and binary covalent compounds. Examples of binary compounds include water (H2O), carbon monoxide (CO), hydrochloric acid (HCl), sodium chloride (NaCl), and silicon dioxide (SiO2).

Binary Acids

A binary acid consists of a hydrogen cation bonded to another atom as an anion. Binary acids are also called hydracids. Naming depends on whether the compound is a liquid or whether it exists in gaseous or anhydrous form.


Liquid acids are named:

hydro + nonmetal + ic + acid

Anhydrous or gaseous binary acids are named:

hydrogen + nonmetal “ide”


  • HCl is hydrochloric acid.
  • HF is hydrofluoric acid.
  • HBr is hydrogen bromide.
  • H2S is hydrogen sulfide or dihydrogen sulfide.

Binary Ionic Compounds

The first atom or cation in a binary ionic compound is a metal, while the second atom or anion is a nonmetal. Binary ionic compounds tend to have relatively high melting and boiling points, due to the ionic bond. They often dissolve in water to yield electrolytes.


The name of a binary ionic compound is:

metal + nonmetal “-ide”

If the metal has different oxidation states, the oxidation state is named. You might still see -ous and -ic suffixes, although they have been deprecated.


  • NaCl is sodium chloride.
  • NaF is sodium fluoride.
  • ZnI2 is zinc iodide.
  • Na3P is sodium phosphide.
  • MgO is magnesium oxide.
  • Al2O3 is aluminum oxide
  • CaCl2 is calcium chloride.
  • FeO is iron(II) oxide or ferrous oxide.
  • Fe2O3 is iron(III) oxide or ferric oxide.
  • CuCl2 is copper(II) chloride.

Binary Covalent Compounds

Binary covalent compounds form when two nonmetals form a covalent bond. This type of compound is also called a binary molecular compound. Often, two nonmetals combine in a variety of ratios. For example, nitrogen and oxygen form NO, NO2, and N2O.


Because there are different combinations of elements in binary covalent compounds, their names include prefixes to indicate the number of atoms.

Number of AtomsPrefix
Numerical prefixes for covalent binary compounds
  1. The more electronegative element appears first in the compound formula. The order of elements is C, P, N, H, S, I, Br, Cl, O, F. However, there are exceptions. Carbon always appears first in binary carbon compounds. Hydrogen appears after nitrogen (e.g., NH3).
  2. A prefix is applied if there is more than one atom of an element in the cation. The mono- prefix is applied to the anion (e.g. CO is carbon monoxide).
  3. The second element is named following the first element, but its ending becomes -ide (e.g., .
  4. If the element name begins with a vowel, the a or o is dropped when a prefix is applied. For example, tetroxide is correct rather than tetraoxide.
  5. The common names are used rather than the formal names for some binary covalent compounds, such as water and ammonia.


  • NO is nitrogen monoxide.
  • CO2 is carbon dioxide.
  • CCl4 is carbon tetrachloride.
  • SF6 is sulfur hexafluoride.
  • N2O is dinitrogen monoxide.
  • N2O4 is dinitrogen tetroxide.
  • S2Cl2 is disulfur dichloride.
  • Cl2O7 is dichlorine heptoxide.
  • H2O is water rather than dihydrogen monoxide.
  • NH3 is ammonia rather than nitrogen trihydride or hydrogen nitride.


  • Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.
  • Whitten, Kenneth W.; Davis, Raymond E.; Peck, M. Larry (2000). General Chemistry (6th ed.). Fort Worth, TX: Saunders College Publishing/Harcourt College Publishers. ISBN 978-0-03-072373-5.