A metallic bond can be defined as follows:
Metallic Bond – the electrostatic attraction between delocalised electrons and positive metal ions.
As the name suggests, metallic bonds are the bonds that hold the atoms in a metal together.
The outer shell electrons of the atoms in a metal are delocalised.
A delocalised electron can be defined as follows:
Delocalised Electron – an electron within an ion, solid metal or molecule that isn’t associated with a single atom or covalent bond.
These electrons are free to move and the atoms are essentially positive ions fixed in position. There is a strong force of attraction between these negative electrons and positive ions – this is the bond that holds the atoms together.
The diagram below illustrates this, with the positive charges representing the ‘ions’ and the negative charges representing the delocalised electrons.
IMPORTANT – although the atoms outer electrons are delocalised, they have not been lost. Therefore they are still technically atoms and not full ions.
Strength and Metallic Bonding
The more outer shell electrons a metal has the stronger the metallic bonds are. There will be more delocalised electrons and the atoms will have a greater positive charge.
For example, lithium has one electron in its outer shell that becomes delocalised. This leaves each atom with a positive charge of one.
Magnesium has two electrons in its outer shell. Both electrons delocalise and each atom has a positive charge of two. The increased number of delocalised electrons combined with the increased charge of the ‘ions’ increases the strength of the attraction.
The metallic bonding is therefore greater in magnesium than lithium.
Properties of Metals
Electrical Conductivity
The delocalised electrons can move freely and so electricity can be conducted.
Melting and Boiling Points
Metals usually have high melting and boiling points. Their regular structures are rigid and the metallic bonds are strong. To dislodge the ‘ions’ and break the bonds high temperatures are required.
Ductility
Metals are ductile which means they can be drawn out. In other words they can be stretched. For example, copper can be drawn out into electrical wires.
Malleability
As well as being ductile, most metals are malleable. This means that they can be pressed or hammered into a shape without cracking.
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