Lesson summary
2.7 Metallic bonding Core — Notes — IGCSE Chemistry notes: Describe metallic bonding and explain the properties of metals and alloys, and compare the main types of structure.Giant structure: metals consist of a giant lattice of positive metal ions in a regular arrangement.Ion for…
- Delocalised electrons
- Ion formation: the atoms lose their outer electrons and become positively charged ions
- Occurs in metals and alloys, which are mixtures of metals
- Melting points vary between metals, so avoid absolute claims
- Metals are good conductors of heat and electricity
- Malleable: can be hammered into shape
Unit 2 · Lesson 2.7
Metallic bonding Core
Describe metallic bonding and explain the properties of metals and alloys, and compare the main types of structure.
Structure of a metal
1
Giant structure: metals consist of a giant lattice of positive metal ions in a regular arrangement.
2
Ion formation: the atoms lose their outer electrons and become positively charged ions.
3
Delocalised electrons: the released outer electrons no longer belong to one atom and move freely between the ions like a sea of electrons.
4
Occurs in metals and alloys, which are mixtures of metals.
The metallic bond
The metallic bond
Metallic bond: the strong force of electrostatic attraction between the positive metal ions and the delocalised electrons.
A diagram must show both the lattice of positive ions and the delocalised electrons.
Melting and boiling points
Melting and boiling points
High melting and boiling points: strong electrostatic forces of attraction between the positive ions and the delocalised electrons need a lot of energy to overcome.
Melting points vary between metals, so avoid absolute claims.
Electrical and thermal conductivity
Electrical and thermal conductivity
Metals are good conductors of heat and electricity.
Reason: the delocalised electrons are free to move through the whole structure and carry charge or energy.
Only electrons move: in a solid metal the positive ions stay in the lattice, whereas molten or aqueous ionic compounds conduct because ions move.
Malleable and ductile
1
Malleable: can be hammered into shape.
2
Ductile: can be pulled into wires.
3
Reason: the layers of positive ions slide over each other when a force is applied, while the attraction to the delocalised electrons is kept.
4
Contrast with ionic crystals: sliding would bring like charges together and the crystal would break.
Alloys
1
Alloy: a mixture of a metal with one or more other elements, so it is not a compound.
2
Harder than the pure metal: atoms of different sizes disrupt the regular layers so they cannot slide as easily.
3
Brass is copper and zinc.
4
Stainless steel is iron with chromium, nickel and carbon, which resists rusting.
Comparing structures
| Structure | Particles | Bonding | Melting point | Conducts? |
|---|---|---|---|---|
| Giant ionic | Positive and negative ions | Electrostatic attraction between ions | High | Only when molten or aqueous |
| Giant metallic | Positive ions and delocalised electrons | Electrostatic attraction between ions and electrons | Usually high | Yes, solid and liquid |
| Simple molecular | Molecules | Weak intermolecular forces between molecules | Low | No |
| Giant covalent | Atoms | Strong covalent bonds throughout | Very high | No (except graphite) |
1
Identify the particles: ions, molecules, atoms, or metal ions with electrons.
2
Identify the bonding: ionic, covalent or metallic.
3
Decide what must be overcome to melt it: strong bonds throughout, or weak intermolecular forces.
4
Predict the melting point and look for mobile charged particles to predict conductivity.
5
Link properties to uses, such as hardness to cutting tools and conductivity to electrodes.
More from the specification
More from the specification
Corrosion passivation by surface oxide
- Corrosion passivation by surface oxide unreactive surface oxide films insulate base metals from air, providing an effective means of environmental protection.
Electron-Sea Model of Metallic Bonding
- Metallic bonding is the electrostatic attraction between a regular crystalline lattice of positive metal cations and a surrounding sea of mobile, delocalised valence electrons.
Electrical and Thermal Conductivity of Metals
- The presence of delocalised electrons free to drift through the metallic lattice under an applied potential difference makes metals outstanding electrical and thermal conductors.
Malleability and Ductility of Metals
- When subjected to mechanical force, layers of uniform metal ions can slide smoothly over one another without shattering the non-directional metallic bonds,
- allowing metals to be hammered into sheets or drawn into wires.
Diamond
- A very hard form of carbon.
Oxygen
- A gas that relights a glowing splint.
Mineral
- A compound containing an element the body needs, such as iron or calcium.
Key terms
| Term | Meaning |
|---|---|
| Metallic bond | the strong electrostatic attraction between positive metal ions and delocalised electrons. |
| Delocalised electrons | outer electrons that move freely between the metal ions. |
| Malleable | able to be hammered into shape. |
| Ductile | able to be drawn into wires. |
| Alloy | a mixture of a metal with one or more other elements. |
Avoid these mistakes
1
Saying metals conduct because ions move: the delocalised electrons move.
2
Calling the electrons free: write delocalised.
3
Saying the metallic bond is between metal atoms only: it is between positive ions and delocalised electrons.
4
Saying an alloy is a compound: it is a mixture.