What Is an Ion?
A neutral atom has equal numbers of protons and electrons, so its charges cancel out. If it gains or loses electrons, the charges no longer balance and the atom becomes an ion — a charged particle.
- Lose electrons → more protons than electrons → positive ion (called a cation)
- Gain electrons → more electrons than protons → negative ion (called an anion)
Metal atoms typically lose electrons to form positive ions. Non-metal atoms typically gain electrons to form negative ions. This is why ionic bonds usually form between a metal and a non-metal.
How Many Electrons Are Transferred?
Atoms want a full outer shell. The number of electrons transferred depends on how many electrons are needed to achieve this:
| Atom | Outer electrons | Electrons lost/gained | Ion formed |
|---|---|---|---|
| Sodium (Na) | 1 | −1 (loses 1) | Na⁺ |
| Magnesium (Mg) | 2 | −2 (loses 2) | Mg²⁺ |
| Chlorine (Cl) | 7 | +1 (gains 1) | Cl⁻ |
| Oxygen (O) | 6 | +2 (gains 2) | O²⁻ |
Ionic Bonding
When a metal and a non-metal react, electrons transfer from the metal to the non-metal. The resulting opposite ions attract each other strongly — this is ionic bonding.
Example: Sodium chloride (table salt)
Na (2,8,1) → Na⁺ (2,8) + e⁻
Cl (2,8,7) + e⁻ → Cl⁻ (2,8,8)
Na⁺ and Cl⁻ attract → NaCl
The ions arrange into a regular lattice (3D grid), held together by electrostatic forces in all directions.
Properties of Ionic Compounds
- High melting points — strong electrostatic forces require a lot of energy to break
- Solid at room temperature — ions held in fixed positions in the lattice
- Conduct electricity when dissolved in water or melted — ions become free to move and carry charge
Real world: Table salt dissolving in water
When you dissolve table salt (NaCl) in water, the ionic lattice breaks apart into free Na⁺ and Cl⁻ ions. These ions can move freely through the water, which is why salt water conducts electricity. This is the basis for how sports drinks replenish electrolytes — they contain Na⁺, K⁺, and other ions that the body needs.
Real world: Limescale in kettles
Hard water contains calcium ions (Ca²⁺) and bicarbonate ions (HCO₃⁻). When you boil hard water, a reaction forms calcium carbonate (CaCO₃) — the white limescale you see in kettles. This is an ionic reaction depositing solid calcium carbonate onto the heating element, reducing its efficiency.
Real world: Electrolysis in industry
Ionic compounds conduct electricity when molten or dissolved. Industry uses this to extract reactive metals: aluminium is extracted from molten aluminium oxide (Al₂O₃) by passing electricity through it. The Al³⁺ ions migrate to the negative electrode and are deposited as aluminium metal. Without ionic bonding, this process would be impossible.
Where do you see this in real life? Your blood contains Na⁺, K⁺, Ca²⁺, and Cl⁻ ions that regulate nerve signals, muscle contractions, and fluid balance. Electrolytes in sports drinks are simply ions in solution — the same chemistry you study here.