2.2.4Structure, Bonding and the Properties of Matter
Properties of Metallic Compounds
5 min read 4 parts Lesson 10 of 14 1 quiz
Section 1 of 4Structure of a Metal
A metal is a regular arrangement of positive ions surrounded by mobile outer electrons.
Positive ions
- Metals contain a regular arrangement of positively charged metal ions that make up the framework of the structure.
Delocalised electrons
- The outer electrons of the metal atoms are free to move through the whole structure rather than belonging to one atom.
Metallic bonding
- The attraction between the positive ions and the sea of delocalised electrons holds the metal together.
Layers
- Layers of ions can slide over one another, which explains why pure metals are often malleable.
Section 2 of 4Conducting Electricity and Heat
Both electrical and thermal conduction depend on the freedom of the delocalised electrons.
1
A potential difference across the metal makes the delocalised electrons drift in one direction, giving an electric current.
2
Because the electrons move freely, they transfer thermal energy quickly from hotter regions to cooler regions of the metal.
3
Vibrating metal ions also pass energy along, but the mobile electrons do most of the heat transfer.
4
Since metals contain many delocalised electrons, they conduct electricity well in the solid state.
Section 3 of 4Comparing Conductivity
Comparing Conductivity
Metals
- Mobile delocalised electrons conduct both electricity and heat in the solid state.
Ionic solids
- Ions are fixed when solid, so the solid does not conduct; it conducts when molten or dissolved.
Graphite
- Delocalised electrons between its layers allow graphite to conduct, unlike diamond.
Simple molecules
- No free charged particles exist, so simple molecular substances are insulators.
| Substance | Mobile charge carriers | Conducts when solid? |
|---|---|---|
| Copper | Delocalised electrons | Yes |
| Sodium chloride | Ions (only when molten or dissolved) | No |
| Diamond | None | No |
Section 4 of 4Exam Checklist & Tips
2.2.4 – Key Points for the Exam
- Delocalised electron An outer electron that is free to move through the whole structure of a metal.
- Metallic bonding The electrostatic attraction between metal ions and the sea of delocalised electrons.
- Alloy A mixture of a metal with another element that has modified properties compared with the pure metal.
- Thermal conductivity The ability of a material to transfer heat energy through it.
Common Mistakes
- Describing metallic bonding as the sharing of electrons between two atoms, as in a covalent bond.
- Saying metal ions move through the metal to carry the current, when it is the electrons that move.
- Stating that metals conduct because they contain ions, without linking conduction to delocalised electrons.
- Forgetting that alloys are harder because their mixed atoms disrupt the layers, making them harder to slide.