Binary compounds: formation, types, examples, nomenclature

For example, water, H 2 O, is a binary compound, perhaps the most representative of them. Water is made up of hydrogen, H, and oxygen, O, thus adding two chemical elements. Note that its stoichiometric coefficients indicate that there are two hydrogen atoms and one oxygen atoms, but it is still a binary compound.

Binary compounds can consist of ions, molecules, three-dimensional networks, or even neutral metal atoms. The important thing is that whatever the nature of its chemical bond or its composition, it is always made up of two different chemical elements. For example, hydrogen gas, H 2 , does not count as a binary compound.

How are binary compounds formed?

The methods of preparation or the synthetic routes to form the binary compounds will depend on the identities of the two chemical elements A and B. However, in principle and in general, both elements must be combined in a reactor so that they can interact with each other. Thus, if conditions are favorable, a chemical reaction will take place.

Having a chemical reaction, elements A and B will join or link (ionically or covalently) to form the compound A n B m . Many binary compounds can be formed by the direct combination of their two pure elements, or by following alternative, more economically viable methods.

Going back to the example of water, hydrogen, H 2 , and oxygen, O 2 , combine at high temperatures so that there is a combustion reaction between them:

2H 2 (g) + O 2 (g) → 2H 2 O (g)

Water, on the other hand, can be obtained through dehydration reactions of compounds such as alcohols and sugars.

Another example of the formation of a binary compound corresponds to ferrous sulfide, FeS:

Fe (s) + S (s) → FeS (s)

Where this time, both iron and sulfur are solid substances and not gaseous. And so it is with various binary salts, for example, sodium chloride, NaCl, combining metallic sodium with chlorine gases:

2Na (s) + Cl 2 (g) → 2NaCl (s)


The names of all binary compounds are mostly governed by the same rules.

For compound A n B m , the name of element B in its anionic form is mentioned first; that is, with the ending -uro. However, for the case that B consists of oxygen, it is named as an oxide, peroxide or superoxide as applicable.

Finally, the name of element A is mentioned. In the event that A has more than one valence, this is indicated with Roman numerals and between parentheses. Or if you prefer, you can opt for the traditional nomenclature and use the suffixes –oso and –ico. The element A is also sometimes preceded by the Greek numeral prefixes according to the value of n .

Consider the following binary compounds together with their respective names:

-H 2 O: hydrogen oxide or dihydrogen monoxide (the latter name is a source of ridicule)

-FeS: iron (II) sulfide or ferrous sulfide

-NaCl: sodium chloride or sodium chloride

-MgCl 2 : magnesium chloride, magnesium chloride, or magnesium dichloride

Note that it does not say ‘monosodium chloride’ or ‘mono iron sulfide’.

Types: classification of binary compounds

Binary compounds are classified according to what they are made of or made of: ions, molecules, metal atoms, or networks. Even so, this classification is not entirely conclusive or definitive, and may vary depending on the approach considered.


In ionic binary compounds, A and B consist of ions. Thus, for the compound A n B m , B is usually an anion, B  , while A a cation, A + . For example, NaCl belongs to this classification, as do all binary salts, the general formulas of which are best represented as MX, where X is an anion, and M a metal cation.

Thus, fluorides, chlorides, bromides, iodides, hydrides, sulfides, arsenides, oxides, phosphides, nitrides, etc., also belong to this classification. However, it should be noted that some of them are covalent, therefore belonging to the following classification.


Covalent binary compounds are made up of molecules. Water belongs to this classification, as it consists of HOH molecules. Hydrogen chloride, HCl, is also considered a covalent binary compound, as it consists of H-Cl molecules. Note that NaCl is ionic, while HCl is covalent, both being chlorides.

Metallic or nets

Binary compounds also encompass alloys and solids in three-dimensional lattices. However, the naming of binary materials is often better used for them.

For example, brass, rather than a compound, is considered a binary material or alloy, as it is made up of copper and zinc, Cu-Zn. Note that CuZn is not written because it does not have defined stoichiometric coefficients.

Likewise, there is silicon dioxide, SiO 2 , made up of silicon and oxygen. Its atoms are linked defining a three-dimensional network, where one cannot speak of molecules or ions. Many nitrides, phosphides and carbides, when they are not ionic, are also treated of this type of network.

Examples of binary compounds

Water is an example of a binary compound

It will be listed to finalize several binary compounds accompanied by their respective names:

-LiBr: lithium bromide

-CaCl 2 : calcium chloride

-FeCl 3 : iron (III) chloride or ferric chloride

-NaO: sodium oxide

-BeH 2 : beryllium hydride

-CO 2 : carbon dioxide

-NH 3 : nitrogen trihydride or ammonia

-PbI 2 : lead (II) iodide or lead diiodide

-Mg 3 N 2 : magnesium nitride

-Al 2 O 3 : aluminum oxide or dialuminum trioxide

-Na 3 P: sodium phosphide

-AlF 3 : aluminum fluoride

-RaCl 2 : radium chloride or radium dichloride

-BF 3 : boron trifluoride

-RbI: rubidium iodide

-WC: tungsten carbide or tungsten

Each of these examples can have more than one name at a time. Of these, CO 2 has a great impact on nature, as it is used by plants in the photosynthesis process .

On the other hand, NH 3 is one of the substances with the highest industrial value, necessary for endless polymeric and organic synthesis. And finally, the toilet is one of the hardest materials ever created.

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