Bonding

Metallic Structures

Metallic Structures

Bonding in metals

In metallic bonding the attraction is between cations and a mass of delocalised electrons. The electrons move between the cations which form a lattice. This lattice structure depends on the metal.

Properties of metals

There are three main properties of metals:

  • Electrical conductivity: the electrons in metals are delocalised. This means that when a potential difference is applied they can move in a certain direction and, therefore, conduct electricity. This is the case whether the metal is in a solid state or a liquid state.
  • Melting and boiling points: the attraction between ions is not as strong as in ionic compounds however it is still strong. This means that the melting and boiling points are relatively high.
  • Non-directional bonding: non-directional bonding means that it does not matter how cations are oriented in terms of each other as there are always delocalised electrons around to hold them together. This means that cations are able to move over each other quite easily making most metals are ductile and malleable.

Ionic Structures

Bond in ionic compounds – A level chemistry revision

Oppositely charged ions form ionic bonds. Once formed, ions build up lattices. In this structure, all cations are surrounded by anions and all anions are surrounded by cations.

The number of oppositely charges ions which surround an ion within an ionic solid is its coordination number. Different substances have different coordination numbers however they tend to be 4, 6 or 8.

Melting and boiling points

The melting and boiling points of an ionic compound are very high because the attraction between ions is very strong. A lot of kinetic energy is needed to overcome this attraction.

As a liquid, the ions are still charged and so the attraction between them is still very high. In order to separate ions completely a lot more energy is needed. Therefore, the difference between the melting and boiling points is large.

The smaller ions the are and the higher their charge, the stronger their attraction to each other and, therefore, the higher the melting and boiling points.

Electrical conductivity

Ionic compounds are composed of ions. This means that electric fields attract them and so they will, if possible, be attracted to electrodes and, thereby, conduct electricity. In a solid state this is not possible since the ions are not able to move freely. This means that they cannot conduct electricity making them good insulators.

However, as a liquid the ions are free to move around and so a ionic compound in this state can now conduct electricity.

Mechanical properties

Ions are held strongly in place by other ions. This makes ionic structures hard and brittle as the ions are not able to move over one another easily.