What does cation mean?
A cation is an ion that carries a positive electric charge. Ions are atoms or molecules whose total number of electrons no longer matches their protons; when an atom loses one or more electrons, it becomes positively charged and is called a cation. In electrolysis and other electrochemical processes, cations migrate toward the negatively charged electrode, known as the cathode — a handy memory aid, since both words share their opening syllable. Common examples include sodium (Na⁺), potassium (K⁺), calcium (Ca²⁺), and hydrogen ions. The term is indispensable across chemistry, from describing how batteries work to explaining how water softeners and soil exchange nutrients through cation exchange. Its opposite is the anion, a negatively charged ion. Though technical in register, 'cation' appears regularly in science education, laboratory work, and popular explanations of electricity and chemistry.
nounA positively charged ion, formed when an atom or molecule loses one or more electrons and which migrates toward the cathode (negative electrode) in electrolysis.
- A positively charged ion that moves toward the cathode in an electric field.
"In a sodium chloride solution, the sodium cations drift toward the negative electrode during electrolysis."
"Hydrogen cations accumulate at the cathode during the electrolysis of water."
"Soil chemists measure the soil's capacity to hold calcium and magnesium cations."
Regular plural; commonly used when discussing multiple ionic species in solution.
"The membrane allows only small cations to pass through."
The word 'cation' was coined by William Whewell at Michael Faraday's request — and its 'cat-' has nothing to do with cats: it comes from the Greek for 'down'.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of cation
The word 'cation' was coined in the early nineteenth century by English polymath William Whewell, who devised the terms 'cation' and 'anion' at Michael Faraday's request during Faraday's pioneering work on electrolysis. It derives from the Greek 'kation', meaning 'that which goes down', from 'kata-' (down) plus 'ion' (going), reflecting the movement of these charged particles toward the cathode. The same Greek root 'kata-' appears in English words such as 'catastrophe' and 'catalogue', while 'anion' is its direct counterpart from 'ana-' (up).
Related word forms
How cation is actually used
A technical term used chiefly in chemistry, physics, and related sciences; rare outside scientific writing. Plural is regular ('cations'). The stress falls on the first syllable, with '-ion' pronounced as in 'ion'.
Easily confused with cation
A cation carries a positive charge while an anion carries a negative charge; they also differ in pronunciation — cation's first vowel sounds like 'cat', whereas anion begins like 'ann'.