Metallic bonding and high melting and boiling points

A metal has a giant structure made up of positive metal ions and delocalised electrons. The electrons are not attached to individual ions; they can move throughout the structure.

The positive ions and the negatively charged delocalised electrons attract each other strongly. This electrostatic attraction is called metallic bonding. It acts throughout the giant lattice, holding the structure together.

Melting and boiling metals

A large amount of energy is needed to overcome the strong attractions between the ions and delocalised electrons. When a metal melts, enough of these attractions must be overcome for its particles to move past one another. Boiling requires the particles to become much more widely separated.

This is why most metals have high melting and boiling points: a large amount of energy must be supplied to overcome the metallic bonding.

Malleability of pure metals

A pure metal can generally be bent or shaped without shattering. This ability is called malleability.

In a pure metal, the atoms are arranged in regular layers. When a force is applied, whole layers can slide past one another, changing the shape of the metal.

The layers can move without the metallic bonding being completely broken. Metallic bonding is the attraction between positive metal ions and delocalised electrons, which are free to move through the metal. As the layers slide, this attraction continues to hold the metal together.

Hardness of alloys

An alloy is a mixture of a metal with other elements, often other metals. Pure metals can be too soft for many uses, so they are mixed with other elements to make harder alloys.

In a pure metal, atoms are arranged in regular layers. When a force is applied, these layers can slide over one another, allowing the metal to change shape.

In an alloy, the atoms of the added elements are often different sizes from the atoms of the main metal. They disrupt the regular arrangement of the layers. This makes it harder for the layers to slide over one another when a force is applied, so the alloy is harder to deform.