Metallic Bonding

The Basics

Metallic bonding involves the attraction between positive metal ions and the sea of delocalised electrons surrounding them.
Metal atoms release their outer shell electrons, becoming positive ions. These released electrons become delocalised and move freely between the positive ions.
This bond type is responsible for the unique properties of metals such as conductivity, malleability, and ductility.

Conductivity

Conductivity in metals is due to the existence of delocalised electrons which can move freely, allowing the transfer of electricity and heat.
When an electric field is applied, these free electrons move, resulting in a current. This results in the high electrical conductivity of metals.
In terms of heat, these electrons can absorb thermal energy and transport it through the lattice structure, accounting for the good thermal conductivity of metals.

Malleability and Ductility

Metals display malleability, the ability to be hammered or rolled into sheets, and ductility, the ability to be drawn into wires. Both properties are due to the metallic bonding structure.
When forces are applied, the layers of ions can slide over each other without breaking the bonds as the delocalised electrons can move and adjust to the new positions of the ions.
This prevents the layers from becoming forced apart, allowing the metal to sustain its structure while changing shape.

Effect of Bonding on Melting/Boiling Point

Metallic bonds are generally strong due to the electrostatic attraction between the positive ions and delocalised electrons.
The strength of a metallic bond and hence the melting/boiling point of a metal is influenced by the number of delocalised electrons per atom (more electrons result in stronger bonds) and the size/charge of the metal ions (smaller and more charged ions result in stronger bonds).
For example, metals like Sodium (Na) have a lower melting/boiling point compared to metals like Iron (Fe) due to fewer delocalised electrons and larger ions, resulting in weaker bonds.

Effect of Bonding on Density

Metals generally have high densities due to the close packing of their ions in the metallic lattice.
The density of a metal is also influenced by the mass of the ions and the size of the metallic structure; heavier ions and smaller structures result in higher densities.
Nevertheless, there are variations among metals, for example, aluminium is less dense than iron due to its larger atomic radius and lighter ion.