2.3.1Additional lessons
Properties of Metals and Their Uses — IB Chemistry SL Revision Notes & Topical Questions
5 min read 6 parts Lesson 33 of 98
Part 1 of 6Metallic Bonding
A metal can be pictured as positive ions held together by a shared sea of electrons.
Lattice of cations
- Metal atoms lose their outer electrons and the resulting positive ions are arranged in a regular lattice.
Delocalised electrons
- The outer electrons are not attached to any one ion but move freely throughout the structure.
Electrostatic attraction
- The attraction between the positive ions and the sea of delocalised electrons is the metallic bond.
Strength
- The bond is stronger when metal ions have a higher charge and a smaller radius, giving more delocalised electrons per ion.
Part 2 of 6Explaining the Properties
Explaining the Properties
Electrical conduction
- Delocalised electrons carry charge through the metal when a potential difference is applied.
Thermal conduction
- Mobile electrons and vibrating ions pass kinetic energy quickly through the lattice.
Malleable and ductile
- Layers of ions slide over one another while the electron sea keeps the bonding intact,
- so the metal changes shape without breaking.
Lustre
- Delocalised electrons reflect light, giving most metals their shiny appearance.
Part 3 of 6Melting Points and Strength
1
Melting a metal requires enough energy to loosen the lattice so that the ions can move past each other.
2
Sodium has one delocalised electron per atom and a large ion, so its metallic bonding is weak and it melts at 98 °C.
3
Magnesium contributes two electrons per atom and has a smaller ion, so it melts higher, at 650 °C.
4
Aluminium contributes three electrons per atom, giving stronger bonding and a melting point of 660 °C.
5
Therefore a greater ionic charge and a smaller ionic radius lead to stronger metallic bonding and a higher melting point.
| Metal | Electrons delocalised per atom | Melting point / °C |
|---|---|---|
| Na | 1 | 98 |
| Mg | 2 | 650 |
| Al | 3 | 660 |
Part 4 of 6Uses Related to Properties
Electrical wiring
- Copper is ductile and an excellent conductor, so it is drawn into wires for cables.
Cooking pans
- Metals conduct heat well and are malleable, so pans and pots are made from them.
Construction
- The strength and hardness of iron-based metals allow them to support buildings and bridges.
Aircraft and cans
- Aluminium has a low density and is easily shaped, so it is used in aircraft parts and drinks cans.
Part 5 of 6Worked Example
Question Explain why magnesium has a higher melting point than sodium.
- Magnesium atoms each release two electrons to the delocalised sea, compared with one for sodium.
- The Mg²⁺ ion has a higher charge and is smaller than Na⁺, so it attracts the electrons more strongly.
- The metallic bonding is therefore stronger and more energy is needed to loosen the lattice.
Answer Mg has stronger metallic bonding because of the higher ion charge, smaller radius and more delocalised electrons, so it has a higher melting point.
Part 6 of 6Exam Checklist & Tips
2.3.1 – Key Points for the Exam
- Metallic bond The electrostatic attraction between metal cations and delocalised electrons.
- Delocalised electrons Electrons that are free to move throughout a metal lattice.
- Malleable Able to be hammered into shape without breaking.
- Ductile Able to be drawn into wires.
Common Mistakes
- Saying that metals contain free atoms or electrons only; the structure contains cations and electrons.
- Claiming the electrons are bonded to specific atoms.
- Forgetting to describe both the cations and the electrons when defining metallic bonding.
- Stating that metals conduct because ions move; in a solid metal the electrons carry the charge.
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