Metallic Bonding

Seite 1

Introduction to Metals

Metals usually have the following properties:

High melting temperature

Good electrical conductivity

Good thermal conductivity

Malleability

Ductility

Between one and three electrons in their outer shells

Low ionisation energies

Increasing electrical conductivity with increasing number of outer electrons

These properties are largely due to the presence of delocalised electrons - electrons that are free to move throughout the structure without being localised between any pair of cations.

There is an electrostatic force of attraction between the nuclei of the cations and the delocalised electrons which is known as metallic bonding.

Seite 2

Melting Points of Metals

Typically metals have very high melting temperatures.

Generally an increase in the number of delocalised electrons per ion leads to an increase in the melting point of the metal.

Group 1 metals have slightly lower melting temperatures

Group 2 have slightly higher melting temperatures

Metals in the d-block have high melting temperatures

Smaller cation → Delocalised electrons closer to nucleus → Stronger forces of attraction → Higher melting point

Seite 3

Conductivity of metals

Electrical Conductivity

When a potential difference is applied across the ends of a piece of metal, the delocalised electrons move towards the positive terminal of the cell.

The movement of charge carriers, in this case electrons, constitutes an electric current.

Thermal conductivity

There are two factors which contribute to the high thermal conductivity of metals:

Delocalised electrons can pass kinetic energy along the metal

Cations are closely packed and can easy pass kinetic energy from one cation to the other

Seite 4

Malleability and Ductility

Malleability: Can be hammered or pressed into different shapes

Ductility: Can be drawn into wire

As shown in the diagram below, when a stress is applied to a metal, layers of cations may slide over each other. However, since the delocalised electrons are free moving, they move with the cations and prevent strong forces of repulsion forming between the cations in one layer and the cations in another layer.