2.2.4Structure, Bonding and the Properties of Matter
Properties of Metallic Compounds
5 min read 11 parts Lesson 10 of 14 1 quiz
Section 1 of 11Structure of a metal
Regular lattice
- Regular lattice A metal consists of positive metal ions arranged in a regular pattern of layers.
Sea of delocalised electrons
- Sea of delocalised electrons The outer electrons of the metal atoms are not tied to any one atom.
- They move freely through the whole structure.
- These are called delocalised electrons.
Metallic bonding
- Metallic bonding The strong electrostatic attraction between the positive ions and the delocalised electrons holds the structure together.
- This is metallic bonding.
Section 2 of 11Electrical conductivity (HT only in some courses)
1Voltage applied
- Voltage applied A cell or battery pushes on the charged particles in the metal.
2Electrons move
- Electrons move The delocalised electrons are free, so they drift through the structure in one direction.
3Charge carried
- Charge carried Moving electrons are a flow of charge, which is an electric current.
4Metal conducts
- Metal conducts This works for solid and liquid metals, because the delocalised electrons are present in both.
Section 3 of 11Other properties explained
| Property | Explanation |
|---|---|
| Conducts heat | Delocalised electrons move through the metal and pass on their kinetic energy quickly, so thermal energy is transferred well |
| High melting and boiling points | The electrostatic attraction between ions and electrons is strong and needs a lot of energy to overcome |
| Malleable (can be hammered and bent) | Layers of ions can slide over one another while the electrons keep the structure bonded |
| Ductile (can be drawn into wires) | The same sliding of layers allows the metal to be stretched without breaking |
| Shiny when cut | The delocalised electrons interact with light at the surface |
Section 4 of 11Alloys
Mixing metals
What an alloy is
- What an alloy is An alloy is a mixture of a metal with another metal or a non-metal, such as brass (copper and zinc) or steel (iron and carbon).
Different sized atoms
- Different sized atoms The atoms of the added element are a different size, which disrupts the regular layers.
Harder
- Harder With the layers disrupted they cannot slide as easily, so alloys are usually harder and stronger than the pure metal.
Designed properties
- Designed properties Adding other elements lets engineers change the properties of a metal to suit a particular job.
Section 5 of 11Explaining conduction in an exam
1
State that a metal has positive ions surrounded by a sea of delocalised electrons.
2
Say that the delocalised electrons are free to move through the structure.
3
Link the movement of electrons to carrying charge (electrical conduction) or carrying energy (thermal conduction).
4
Do not say that the ions move. In a solid metal the ions stay in position.
Section 6 of 11Structure 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 7 of 11Conducting 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 8 of 11Comparing 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 9 of 11Exam 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.
Section 10 of 11Key terms
| Term | Meaning |
|---|---|
| Metallic bonding | The electrostatic attraction between positive metal ions and delocalised electrons. |
| Delocalised electrons | Outer electrons that are free to move throughout a metal structure instead of belonging to one atom. |
| Malleable | Able to be hammered or bent into shape without breaking. |
| Alloy | A mixture of a metal with at least one other element, usually another metal. |
| Conductor | A material that lets electric current or heat pass through easily. |
Section 11 of 11Exam technique
1
Saying that metals conduct because their ions move. It is the delocalised electrons that move.
2
Describing the sea of electrons as negative and the structure as negative. The metal as a whole is neutral.
3
Forgetting that metals also conduct heat because of the delocalised electrons.
4
Saying alloys are pure metals. They are mixtures, and the different sized atoms make the layers harder to slide.