Chemical bonds: Metallic bonding occurs in metallic elements and alloys.

The idea

Metallic bonding is the strong electrostatic attraction between a lattice of positive metal ions and a sea of delocalised electrons. This type of bonding is characteristic of all metallic elements, such as copper and iron, as well as alloys, which are mixtures of a metal with at least one other element, like steel or brass. In a solid metal, the outer shell electrons detach from the atoms, leaving behind positively charged ions arranged in a regular, repeating three-dimensional pattern. The delocalised electrons are free to move throughout this giant structure, which explains key metallic properties such as electrical conductivity and malleability.

What earns the marks

• Define metallic bonding as the attraction between positive metal ions and delocalised electrons.
• Identify that metallic bonding occurs in pure metals and alloys.
• Describe the structure of a metal as a giant lattice of positive ions.
• Explain that the outer shell electrons in a metal are delocalised and free to move.

Common mistakes and how to put them right

• Describing metallic bonding as the sharing of electrons between atoms.

  Put it right: Metallic bonding involves a lattice of positive ions and a sea of delocalised electrons.

• Referring to the particles in a metallic lattice as atoms.

  Put it right: The particles in the lattice are positive metal ions.

• Stating that alloys contain ionic bonds because they are mixtures.

  Put it right: Alloys still feature metallic bonding, though the lattice is distorted by different sized atoms.

Exam tips

• Use the phrase 'sea of delocalised electrons' when describing metallic bonding to secure marks.
• Ensure you refer to the fixed particles in the lattice as 'positive ions' rather than 'atoms' or 'protons'.
• Remember that alloys are mixtures, not compounds, but they still rely on metallic bonding to hold their structure together.