Metals have giant structures of atoms with strong metallic bonding.

The idea

Metals are giant structures because their atoms are packed together in enormous numbers. Each atom contributes its outer electrons to a shared pool of delocalised electrons. The positive metal ions sit in a regular lattice and are held to this electron sea by strong electrostatic attraction, known as metallic bonding. Because the bonding extends throughout the whole piece of metal, there are no weak edges or small molecules to pull apart. For example, in a piece of copper, countless Cu atoms are arranged in a lattice with delocalised electrons moving between them. The strength of the bonding explains why metals are generally strong, while the delocalised electrons allow them to conduct electricity.

What earns the marks

• Metals form giant structures, meaning very large numbers of atoms are joined together in one continuous lattice rather than in small molecules.
• Each metal atom releases one or more outer electrons, producing a sea of delocalised electrons and positive metal ions.
• Metallic bonding is the strong electrostatic attraction between the positive metal ions and the delocalised electrons.
• The bonding acts in all directions throughout the giant structure, so there are no weak intermolecular forces between separate metal molecules.
• A correct example, such as copper or magnesium, can be used to show a lattice of positive ions surrounded by delocalised electrons.

Common mistakes and how to put them right

• Saying that metal atoms share pairs of electrons in the same way as covalent bonding.

  Put it right: Outer electrons become delocalised and are shared across the whole lattice.

• Describing metallic bonding as positive ions attracting negative ions.

  Put it right: The attraction is between positive metal ions and delocalised electrons.

• Treating a metal as a collection of separate molecules with weak forces between them.

  Put it right: The whole piece is one giant structure with strong bonding throughout.

Exam tips

• Use the phrase delocalised electrons rather than free electrons when explaining metallic bonding.
• Link the giant structure directly to a property, such as a high melting point or electrical conductivity, to show understanding.
• When drawing a diagram, label the positive metal ions and the delocalised electrons clearly so the examiner can see both parts of the model.