What does valency mean?
Valency is the chemical property describing an atom’s or ion’s combining capacity: how many bonds it can form, or equivalently how many hydrogen atoms it can combine with or replace in a given atom. It is a specialized term used chiefly in chemistry and related scientific disciplines. Carbon’s valency of four is a familiar example and helps explain the enormous variety of carbon-based molecules. The word is more common in British English, while American English generally uses “valence” for the same concept. Valency can also be used more broadly in descriptions of bonding patterns and molecular structure, such as the valency of a central atom or the maximum valency of an element. It is distinct from “value,” “validity,” and “valency” in non-chemical senses, although all of these words share a historical connection with ideas of strength or worth.
nounIn chemistry, the combining capacity of an atom or ion, usually expressed as the number of hydrogen atoms it can combine with or replace in a given atom. The term is chiefly used in British English; American English more commonly uses “valence.”
- The combining capacity of an atom or ion, expressed as the number of bonds it can form or the number of hydrogen atoms it can combine with or replace.
"Carbon has a valency of four, allowing it to form a wide range of chemical bonds."
"Oxygen commonly has a valency of two, forming bonds with many other elements."
"The valency of the central atom strongly influences the structure of the resulting molecule."
The regular plural of “valency,” used when referring to the combining capacities of different atoms or ions.
"The valencies of the atoms in the molecule determine many of its structural features."
Valency explains why carbon can form millions of different molecules: its valency of four lets it link to other atoms in remarkably varied arrangements.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does valency come from?
The word ultimately derives from Latin valere, meaning “to be strong” or “to be worth.” Through the adjective valent, meaning strong or having value, and related English formations such as valence, it developed into the chemical term for combining capacity. The British form “valency” reflects the same Latin root as “valence,” “valid,” “valiant,” and “valor.”
Related word forms
How valency is actually used
This is a specialized chemistry term, usually encountered in formal scientific contexts. “Valency” is especially associated with British usage, whereas American usage tends to prefer “valence.”
Easily confused with valency
“Valency” and “valence” have essentially the same chemical meaning, but “valency” is more common in British English while “valence” is more common in American English.