A

Anion

A^n−
Quick Reference
Formula / NotationA^n−
Also Known AsNegative ion, electronegative ion

What is Anion?

An anion is a negatively charged ion formed when an atom or molecule gains one or more electrons. Anions are attracted to the positively charged anode during electrolysis. Common anions include chloride (Cl⁻), sulfate (SO₄²⁻), nitrate (NO₃⁻), and hydroxide (OH⁻). Non-metals typically form anions by gaining electrons.

Formula & Notation

A^n−

Other Names / Synonyms: Negative ion, electronegative ion

Properties & Characteristics

An anion is a negatively charged ion formed when an atom or group of atoms gains one or more electrons. Anions are attracted to the positively charged anode in electrolysis. Their charge arises from having more electrons than protons. Common anions include chloride (Cl⁻), sulfate (SO₄²⁻), carbonate (CO₃²⁻), and hydroxide (OH⁻). Anion size is generally larger than the parent neutral atom due to increased electron-electron repulsion.

Uses & Applications

Anions are fundamental components of ionic compounds, electrolytes, and salts used across chemistry, biology, and industry. Chloride ions regulate osmotic pressure in biological systems. Sulfate and nitrate anions are essential in fertilisers. Phosphate anions are key structural components of DNA and ATP.

Safety Information

Hazard varies by anion. Cyanide (CN⁻) and azide (N₃⁻) are acutely toxic. Fluoride (F⁻) is toxic at high concentrations. Nitrate and nitrite anions can be hazardous oxidising agents. Always consult the SDS for specific anion compounds before handling.

Always consult the SDS/MSDS before handling any chemical. This information is for educational purposes only.

Key Facts

Term Anion
Formula A^n−
Synonyms Negative ion, electronegative ion

Frequently Asked Questions

An anion is a negatively charged ion formed when an atom or molecule gains one or more electrons. Anions are attracted to the positively charged anode during electrolysis. Common anions include chloride (Cl⁻), sulfate (SO₄²⁻), nitrate (NO₃⁻), and hydroxide (OH⁻). Non-metals typically form anions by gaining electrons.

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