Suitable for
GCSE and A-level Chemistry. Use the first five screens to develop explanations of metallic bonding and properties, then use the A-level comparison to explore factors affecting the strength of metallic bonding.
Learning objectives
Students should be able to:
- Describe metallic bonding as strong electrostatic attraction between positive metal ions and delocalised electrons.
- Explain electrical and thermal conductivity using the behaviour of particles within a metal.
- Relate melting, malleability and alloy hardness to metallic structure and bonding.
- At A-level, compare metallic bonding using positive ion charge, electron contribution and ion size.
Suggested teaching sequence
1. Start with the atoms
Open Structure and establish that each sodium atom has one outer electron. Ask students to predict what will happen when Delocalise is pressed. Use Follow 1 e⁻ to track an electron as it moves beyond its original atom. Pause during the transition to discuss the fading shell guides and the appearance of positive ion labels.
Once the transition finishes, select Show electrostatic attraction. Emphasise that the electrons remain within the metal and that the sample is neutral overall. Replay from atoms restores the starting view.
2. Explain electrical conductivity
On Electricity, observe the electrons before switching on the circuit. They already move randomly. Switching on adds a net drift, and reversing the supply reverses its direction. Compare the solid and molten states, asking students to identify the mobile charged particles responsible for conduction.
3. Explain thermal conductivity
On Heat transfer, heat the left end and watch energy spread through the sample. Draw attention to the larger vibrations in warmer regions. Ask students how energy reaches the far end while the positive ions remain near their fixed positions. Link the explanation to delocalised electrons and the transfer of energy through vibrations.
4. Explore melting
Use the energy slider or Heat to melt to change the solid into a liquid. Students should identify the loss of fixed positions while the particles remain close together. Connect the energy required to the strength of metallic attractions, and establish that metallic bonding and delocalised electrons remain in the liquid.
5. Compare a pure metal and an alloy
Choose a force, then press Apply same force. Compare the movement of layers in the two samples. Ask students to explain how different-sized atoms distort the alloy’s regular arrangement and make sliding more difficult. Notice that the changed shape remains after the force is released.
6. Extend to A-level
Compare sodium, magnesium and aluminium. Hide the melting points first and invite predictions. Link differences in attraction to positive ion charge, the number of delocalised electrons contributed per atom and ion size. Avoid treating melting point as directly proportional to electron count.
Important teaching points
- Delocalised means shared throughout the structure, rather than associated with one atom. The electrons do not escape from the metal.
- Positive ions in a solid vibrate around fixed positions; they do not travel along the metal to carry the current.
- Heating increases particle motion; it does not make individual particles larger.
- Melting does not remove all metallic attraction or spread particles out like a gas.
- Many alloys are harder because their distorted arrangement makes sliding more difficult; their layers are not completely immovable.
Using the model effectively
Use Full screen for projection and ½× speed when introducing a new idea. Pause and Step allow students to describe a change before explaining it. Each screen includes Discuss this model, with a question and revealable explanation.
The opening atom-to-metal sequence is conceptual: outer electrons in an existing metal are already delocalised. Shell circles are guides, not literal electron paths. Particle sizes, movements and force differences are simplified for teaching.