Anion
Definition and meaning of Anion in chemistry.
An anion is an ion that carries a negative electric charge, formed when an atom or molecule gains one or more electrons.
In more detail
The gain of electrons gives an anion more negatively charged particles (electrons) than positively charged particles (protons), resulting in a net negative electric charge. Anions are attracted to the anode (positive electrode) during electrolysis, which is how they derived their name from the Greek prefix "ana-" (meaning up) and the word "ion." This negative charge is essential for forming ionic compounds, where anions pair with positively charged cations to create stable crystalline structures. In biological systems, anions like phosphate (PO4³⁻) and bicarbonate (HCO3⁻) are vital for cellular functions, metabolism, and maintaining proper pH balance.
Key facts
| Field | General Chemistry |
|---|---|
| Charge | Negative |
| Common example | Chloride ion (Cl⁻) |
| Formation method | Electron gain |
When a chlorine atom gains an electron, it becomes a chloride anion (Cl⁻), which combines with sodium cations (Na⁺) to form table salt (NaCl).
Frequently asked questions
How are anions different from cations?
Anions are negatively charged ions formed by gaining electrons, while cations are positively charged ions formed by losing electrons. Both are necessary for forming ionic compounds.
Why do atoms form anions?
Atoms form anions because gaining electrons lowers their overall energy and increases stability. Elements with high electron affinity, such as halogens and oxygen, readily gain electrons to form anions.