The key idea
Metallic bonding is the electrostatic attraction between a lattice of positive metal ions and a sea of delocalised electrons.This explains why metals conduct electricity and heat, and are malleable.
Use the labels to explain the scientific relationship shown.
The bit that matters
Keep the idea tight, then use the worked example to practise the exact exam wording.
Metallic bonding
In a metal, each atom contributes its outer electrons to a 'sea' of delocalised electrons that are free to move throughout the structure.The remaining positive metal ions are arranged in a regular lattice.The metallic bond is the strong electrostatic attraction between the positive ions and the surrounding delocalised electrons.The number of outer electrons each atom contributes affects the strength of the bond.
Properties from metallic bonding
The sea of delocalised electrons explains the key properties of metals: electrical conductivity (electrons carry charge), thermal conductivity (electrons transfer kinetic energy), malleability and ductility (layers of ions slide while electrons maintain bonding).The high melting and boiling points of most metals are due to the strong electrostatic attraction between the ions and the electron sea.
Alloys
An alloy is a mixture of a metal with one or more other elements.Common alloys include steel (iron + carbon), bronze (copper + tin) and brass (copper + zinc).Alloying introduces atoms of different sizes into the lattice, distorting the regular arrangement.This prevents layers from sliding easily, making alloys harder and less malleable than pure metals.
Shape memory alloys and nanoparticles
Shape memory alloys, such as nitinol (nickel + titanium), can return to a memorised shape when heated.They are used in medical devices such as stents and dental braces.Nanoparticles of metals have a very high surface area to volume ratio compared with bulk metals, which can give them different properties such as improved catalytic activity.
Definitions to learn
Metallic bonding
The electrostatic attraction between a lattice of positive metal ions and a surrounding sea of delocalised electrons.
Delocalised electron
An electron that is free to move throughout the metallic lattice rather than being associated with a single atom.
Malleable
Able to be beaten or pressed into shape without breaking.
Ductile
Able to be drawn into a wire without breaking.
Alloy
A mixture of a metal with one or more other elements, usually designed to have improved properties.
Shape memory alloy
An alloy that returns to a predetermined shape when heated, e.g. nitinol.
Explain why metals are good conductors of electricity.
Metal atoms lose their outer electrons to form positive ions.
These electrons become delocalised and move freely throughout the structure.
When a voltage is applied, the delocalised electrons can move in one direction.
This flow of electrons constitutes an electric current.
Metals conduct because of the sea of delocalised electrons that carry charge through the structure.
For any metallic property question, always mention the sea of delocalised electrons and the lattice of positive ions as the starting point.
Do not say metals conduct because they have 'free electrons in their outer shell'.The outer electrons are delocalised — they do not belong to one atom.
How to score full marks
- 1All three metallic properties (conductivity, malleability, high melting point) must be explained using the sea of delocalised electrons — state it explicitly.
- 2For alloy hardness, say 'different-sized atoms distort the lattice, preventing layers from sliding' — all three parts needed.
- 3Do not confuse 'delocalised electrons' in metals with 'free electrons in the outer shell' — they are not attached to a single atom.
Try these yourself
Open each answer only after you have explained the full chemical process.
1State what is meant by delocalised electrons in a metal.[1 mark]
- 1.Describe where these electrons come from and where they are found.
2Explain why metals are malleable (can be beaten into shape).[3 marks]
- 1.Describe what happens to the layers when force is applied.
3Explain why metals have high melting points.[2 marks]
- 1.Link to the strength of metallic bonding.
4Define an alloy.[1 mark]
- 1.Use the words 'mixture' and 'metal'.
5Explain why alloys are generally harder than pure metals.[3 marks]
- 1.Describe the effect of differently sized atoms on layer movement.
6State one example of an alloy and its composition.[1 mark]
- 1.Recall a named alloy.
7Compare the electrical conductivity of a pure metal with that of an alloy and explain the difference.[3 marks]
- 1.Consider how lattice regularity affects electron movement.
8Explain, in terms of structure and bonding, why metals can be drawn into wires (are ductile).[3 marks]
- 1.Apply the sliding-layers argument.