counter-ion: meaning, definition, pronunciation and examples
C2 / Very Low Frequency (Academic/Technical)Formal, Academic, Scientific, Technical
Quick answer
What does “counter-ion” mean?
An ion with an opposite electric charge to a given ion in a system, typically in a solution or ionic crystal.
Audio
Pronunciation
Definition
Meaning and Definition
An ion with an opposite electric charge to a given ion in a system, typically in a solution or ionic crystal.
In chemistry, an ion that accompanies a more important or central ion to maintain overall electrical neutrality. In biochemistry and materials science, the small, mobile ions surrounding a larger, charged macromolecule or colloidal particle.
Dialectal Variation
British vs American Usage
Differences
Spelling: UK English retains the hyphen ('counter-ion'). US English often uses the closed form ('counterion'), though the hyphenated form is also common in academic publications.
Connotations
Identical scientific meaning; no difference in connotation.
Frequency
Extremely rare outside of chemistry, biochemistry, and materials science texts in both varieties. The term's frequency is determined by the technical context, not regional variety.
Grammar
How to Use “counter-ion” in a Sentence
[cation/anion] acts as a counter-ion to [anion/cation][macromolecule] is surrounded by a diffuse layer of counter-ionsThe [salt] dissociates into [ion] and its counter-ion.Vocabulary
Collocations
Examples
Examples of “counter-ion” in a Sentence
verb
British English
- The sodium ions counter-ion the negatively charged polymer backbone.
- No standard verb form exists.
American English
- No standard verb form exists.
adverb
British English
- Not used adverbially.
American English
- Not used adverbially.
adjective
British English
- The counter-ion concentration was measured.
- Counter-ion dynamics were studied via NMR.
American English
- The counterion concentration was measured.
- Counterion dynamics were studied via NMR.
Usage
Meaning in Context
Business
Not used.
Academic
Used in chemistry, biochemistry, physical chemistry, and materials science publications and lectures to describe ionic interactions, electrolyte behaviour, and colloidal stability.
Everyday
Never used.
Technical
Core term in technical manuals for analytical instruments (e.g., ion chromatography), formulations (e.g., pharmaceuticals, detergents), and polymer science.
Vocabulary
Synonyms of “counter-ion”
Strong
Neutral
Weak
Vocabulary
Antonyms of “counter-ion”
Watch out
Common Mistakes When Using “counter-ion”
- Using 'counter-ion' to mean any ion in a mixture, rather than specifically the oppositely charged one relative to a reference ion.
- Confusing 'counter-ion' with 'ligand' (a ligand binds to a central atom via coordinate covalent bonds, not just electrostatic attraction).
- Misspelling as 'counterion' in formal UK academic writing where a hyphen is preferred.
FAQ
Frequently Asked Questions
Both 'counter-ion' (hyphenated) and 'counterion' (closed) are acceptable, with the hyphenated form being more traditional and common in UK English, and the closed form gaining prevalence, especially in US English.
Yes. A counter-ion's charge is always opposite to the ion it is associated with. For a cation (positive), the counter-ion is an anion (negative). For an anion (negative), the counter-ion is a cation (positive).
They are closely related. A spectator ion is a type of counter-ion that does not participate in the net chemical change of a reaction. All spectator ions are counter-ions in the reaction mixture, but not all counter-ions (e.g., those tightly bound to a protein) are merely 'spectators'.
Conceptually, yes. A co-ion is an ion in a system that carries the *same* type of charge (positive or negative) as a specific ion of interest. The counter-ion carries the opposite charge.
An ion with an opposite electric charge to a given ion in a system, typically in a solution or ionic crystal.
Counter-ion is usually formal, academic, scientific, technical in register.
Counter-ion: in British English it is pronounced /ˈkaʊntər ˌaɪən/, and in American English it is pronounced /ˈkaʊn(t)ər ˌaɪən/. Tap the audio buttons above to hear it.
Phrases
Idioms & Phrases
- “none”
Learning
Memory Aids
Mnemonic
Think of a magnet: a north pole needs a south pole. A positive ion (cation) needs a negative 'counter'-ion (anion) to balance it, and vice-versa.
Conceptual Metaphor
ACCOUNTING: The counter-ion is the 'accounting entry' that balances the 'charge ledger'. PARTNER: The counter-ion is the essential partner that neutralises the primary ion's charge.
Practice
Quiz
What is the primary role of a counter-ion?