Ionic bonding

Formation of Ions

  • Cations (positive ions):
    Formed when atoms lose electrons (usually metals).
    Example: Sodium (Na) loses 1 electron → Na⁺.

  • Anions (negative ions):
    Formed when atoms gain electrons (usually non-metals).
    Example: Chlorine (Cl) gains 1 electron → Cl⁻.

Ionic Bond

  • An ionic bond is a strong electrostatic attraction between oppositely charged ions.

Formation of Ionic Bonds

  • Group I + Group VII (metal + non-metal):
    Example: Sodium and Chlorine.

    • Na (Group I) loses 1 electron → Na⁺.

    • Cl (Group VII) gains 1 electron → Cl⁻.

    • Bond forms between Na⁺ and Cl⁻.

    • Shown using dot-and-cross diagrams (electrons from different atoms shown with dots and crosses).

  • General case (metal + non-metal):

    • Metal atoms lose electrons → cations.

    • Non-metal atoms gain electrons → anions.

    • Electrostatic forces hold them in a lattice.

Properties of Ionic Compounds

  • High melting and boiling points:
    Strong electrostatic forces between ions → lots of energy needed to break bonds.

  • Electrical conductivity:

    • Solid: Do not conduct (ions are fixed in lattice).

    • Molten or aqueous: Conduct electricity (ions are free to move and carry charge).

  • Solubility:
    Many ionic compounds are soluble in water (water molecules separate the ions).

Explaining Properties (Structure + Bonding)

  • Ionic compounds have a giant ionic lattice.

  • This is a regular 3D arrangement of alternating positive and negative ions.

  • Example: Sodium chloride (NaCl).

  • Explains:

    • High melting/boiling points (strong bonds in all directions).

    • Conductivity when molten/aqueous (ions free to move).

    • Insolubility in non-polar solvents but usually soluble in water.

Three Types of Bonding

  1. Ionic bonding – between metals and non-metals (transfer of electrons).

  2. Covalent bonding – between non-metals (sharing of electrons).

  3. Metallic bonding – in metals (positive ions in a sea of delocalised electrons).