Chemical bonds: There are three types of strong chemical bonds: ionic, covalent and metallic. For ionic bonding the particles are oppositely charged ions. For covalent bonding the particles are atoms which share pairs of electrons. For metallic bonding the particles are atoms which share delocalised electrons.

The idea

This statement defines the three strong chemical bonds. Ionic bonding occurs between oppositely charged ions, usually a metal and a non-metal, where electrons are transferred to form positive and negative ions. For example, sodium loses one electron to form Na⁺ and chlorine gains one electron to form Cl⁻, giving NaCl. Covalent bonding occurs between non-metal atoms that share pairs of electrons, as in H₂ where each hydrogen shares one pair, or in O₂ where two pairs are shared. Metallic bonding occurs in metals, where positive metal ions are held in a lattice of delocalised electrons. The shared delocalised electrons explain why metals conduct electricity and heat. When describing a bond, state the particles involved and how electrons are involved.

What earns the marks

• Name the three strong chemical bonds as ionic, covalent and metallic.
• Describe ionic bonding as electrostatic attraction between oppositely charged ions, formed by electron transfer.
• Describe covalent bonding as sharing pairs of electrons between atoms, often non-metal atoms.
• Describe metallic bonding as positive metal ions in a lattice with delocalised electrons.
• Use examples such as NaCl, H₂O or Mg to illustrate each bonding type.

Common mistakes and how to put them right

• Saying covalent bonds share single electrons rather than pairs of electrons.

  Put it right: Covalent bonds involve shared pairs of electrons.

• Describing ionic bonding as sharing electrons.

  Put it right: Ionic bonding involves transfer of electrons to form oppositely charged ions.

• Stating that metallic bonding involves shared pairs of electrons between specific atoms.

  Put it right: Metallic bonding involves delocalised electrons shared across the whole metal lattice.

Exam tips

• For each bond type, state the particles involved and how electrons are involved.
• Use a dot-and-cross diagram to support a written description of covalent bonding.
• When comparing bonds, use the terms 'transfer', 'share' and 'delocalised' accurately.