Metals have giant structures of atoms with strong metallic bonding. This…

The idea

Metals are giant structures in which positive metal ions are arranged in a regular lattice and are surrounded by a sea of delocalised electrons. The electrostatic attraction between the positive ions and the shared delocalised electrons is metallic bonding, and it acts in all directions throughout the structure. Because this bonding is strong and extends across the whole giant lattice, a large amount of energy is needed to overcome it, so most metals have high melting and boiling points.

For example: Magnesium melts at about 650 °C and iron at about 1538 °C. Melting point trends can be linked to the strength of metallic bonding: metals with more delocalised electrons per atom and smaller ions often have stronger bonding and higher melting points.

What earns the marks

• Describe a metal as a giant lattice of positive ions with delocalised electrons throughout the structure.
• Explain metallic bonding as the strong electrostatic attraction between positive metal ions and delocalised electrons.
• Link the strength and extent of metallic bonding to the large energy needed to melt or boil the metal.
• State that most metals therefore have high melting and boiling points, and use a named example such as iron or magnesium.
• Compare metals with simple molecular substances, where weak intermolecular forces mean low melting and boiling points.
• Recognise that the same delocalised electrons explain why metals conduct electricity and heat.

Common mistakes and how to put them right

• Saying metallic bonding is between atoms only.

  Put it right: Describe positive metal ions in a lattice with delocalised electrons, and the attraction between them.

• Claiming all metals have equally high melting points.

  Put it right: Most are high, but the strength of metallic bonding varies, so values differ, for example mercury is liquid at room temperature.

• Confusing delocalised electrons with shared pairs in covalent bonds.

  Put it right: In metallic bonding the electrons are delocalised across the whole giant structure, not shared between two specific atoms.

Exam tips

• Always name the two charged or electron parts involved in metallic bonding, then state that the attraction is strong and acts throughout the giant structure.
• When explaining a high melting point, refer to energy needed to overcome the strong metallic bonds, not to breaking individual atoms.
• Use a specific metal and its approximate melting point as evidence, and keep the link between bonding strength and energy explicit.