metallic bonding

Higher and foundation tier

The properties of metals

The general properties of metals can be summarised in the image below:

the properties of maetals

We can use the general properties of metals shown in the image above to help us figure out what the structure of a metal looks like. The table below tries to offer an explanation for some of the properties of metals and relate this property to a possible feature of the metal structure.

Metal property How this relates to its structure
Metals are good conductors of electricity and heat There must be free or delocalised electrons within the structure to conduct the electricity and heat.
Metals have high melting and boiling points. Metals must have a giant structure with lots of strong bonds.
Metals are malleable (can be hammered into shape) and ductile (can be pulled into wire). There are layers of particles that are able to slide over each other.
Metals are shiny. Free or delocalised electrons are able to reflect light at the surface.
Metals are hard and dense The particles within the metal structure are packed tightly together.

The structure of metals

These basic properties of metals allows us to suggest that metals consist of a giant structures of ion with free delocalised electrons. We also already know that metals are found on the left hand side of the periodic table in groups 1, 2 and 3 and that they tend to lose electrons in their reactions to form positively charged ions. This leads us to the model shown below. The dark grey balls represent positively charged metal ions (atoms which have lost their outer shell electrons). These electrons are delocalised and free to move through the giant structure of ions. This might seem odd since we might expect a giant structure of ions, all with a positive charge to repel each other and so the structure would simply break down. However we need to think about the delocalised electrons within the structure.

metallic bonding

metallic bonding The negatively charged electrons are attracted to the positively charged metal ions and this prevents the metal ions from repelling each other (see image opposite). The electrons are attracted to the metal ions around them. This attraction of the negatively charged electrons to the neighbouring positively charged metal ions is called a metallic bond. A key feature of this bond is the fact that metallic bonds are not permanent but are constantly breaking and reforming as the electrons move freely around the structure.

The fact that these metallic bonds are not permanent but are constantly breaking and reforming allows the layers of ions to slide over each other. This is shown in the diagram below, which shows a pushing force being applied to the top two layers of ions in a metal structure. The metallic bonds in these layers immediately break and the layers of ions slide along, but as soon as they stop moving the metallic bonds immediately reform. This is why metals are malleable (hammered into shape) and ductile (can be pulled into wires).

Malleable and ductile

As mentioned above metals can be hammered and beaten into different shapes, that is they are malleable. The diagram below shows that when a force is applied to layers of metal ions within a giant metal structure, the layers of metal ions are able to slide over each other due to the fact that the temporary metallic bonds are continually breaking and reforming. The temporary nature of these metallic bonds also explains why metals can be drawn out into wires, that is they are ductile.

layers sliding in metallic bonding

Practice questions

Check your understanding - Questions on metallic bonding