Cation and Anion — Definition, Examples and Difference

Cation (positively charged ion):

Definition: An ion with a net positive charge, formed when an atom loses one or more electrons.

How cations form: • Metals tend to lose electrons to form cations • Atom → Cation + electrons • Na → Na⁺ + e⁻ (sodium loses 1 electron) • Mg → Mg²⁺ + 2e⁻ (magnesium loses 2 electrons) • Al → Al³⁺ + 3e⁻ (aluminium loses 3 electrons)

Property: Cations have MORE protons than electrons (protons > electrons)

Common cations: Cation | Name | Charge | Formed from H⁺ | Hydrogen / Proton | +1 | H atom loses e⁻ Na⁺ | Sodium | +1 | Na (Group 1) K⁺ | Potassium | +1 | K (Group 1) Ca²⁺ | Calcium | +2 | Ca (Group 2) Mg²⁺ | Magnesium | +2 | Mg (Group 2) Al³⁺ | Aluminium | +3 | Al (Group 13) Fe²⁺ | Iron(II)/Ferrous | +2 | Fe Fe³⁺ | Iron(III)/Ferric | +3 | Fe NH₄⁺ | Ammonium | +1 | N compound Cu²⁺ | Copper(II)/Cupric | +2 | Cu

In electrolysis: Cations move toward the cathode (negative electrode)

Anion (negatively charged ion):

Definition: An ion with a net negative charge, formed when an atom gains one or more electrons.

How anions form: • Non-metals tend to gain electrons to form anions • Atom + electrons → Anion • Cl + e⁻ → Cl⁻ (chlorine gains 1 electron) • O + 2e⁻ → O²⁻ (oxygen gains 2 electrons) • N + 3e⁻ → N³⁻ (nitrogen gains 3 electrons)

Property: Anions have MORE electrons than protons (electrons > protons)

Common anions: Anion | Name | Charge | Formed from Cl⁻ | Chloride | -1 | Cl (Group 17) Br⁻ | Bromide | -1 | Br (Group 17) I⁻ | Iodide | -1 | I (Group 17) F⁻ | Fluoride | -1 | F (Group 17) O²⁻ | Oxide | -2 | O (Group 16) S²⁻ | Sulphide | -2 | S (Group 16) N³⁻ | Nitride | -3 | N (Group 15) OH⁻ | Hydroxide | -1 | OH group NO₃⁻ | Nitrate | -1 | NO₃ group SO₄²⁻ | Sulphate | -2 | SO₄ group CO₃²⁻ | Carbonate | -2 | CO₃ group

In electrolysis: Anions move toward the anode (positive electrode)

Cation vs Anion — Key Differences:

Property | Cation | Anion Charge | Positive (+) | Negative (-) Formation | Loses electrons | Gains electrons Protons vs electrons | More protons | More electrons Typically formed by | Metals | Non-metals Movement in electrolysis | Toward cathode (-) | Toward anode (+) Example | Na⁺, Ca²⁺, Fe³⁺ | Cl⁻, O²⁻, SO₄²⁻

Memory trick: Cat-ion: CAT-ions are PAWSitively charged (Cats have paws, positive = paws = +) A-nion: An-ions are Negative

Or simply: • CATion: Cats are POSITIVE (friendly, positive charge) • ANion: AN-ions are NEGATIVE charges

Ionic compounds: When a cation and anion combine, they form an ionic compound: • Na⁺ + Cl⁻ → NaCl (sodium chloride / table salt) • Ca²⁺ + 2Cl⁻ → CaCl₂ (calcium chloride) • Mg²⁺ + O²⁻ → MgO (magnesium oxide)

In solution: • Ionic compounds dissociate into cations and anions in water • NaCl → Na⁺ + Cl⁻ (in water)