Properties of Metallic CompoundsOxford AQA IGCSE Chemistry: Revision notes
Section 1
What structure do metals have?
Metals consist of a giant structure of atoms arranged in a regular, repeating pattern (a lattice). In metallic bonding, each metal atom loses the electrons in its outer shell to the whole structure, forming a lattice of positively charged metal ions surrounded by a "sea" of delocalised electrons that are free to move throughout the entire structure, not attached to any one atom.
Section 2
Why do metals conduct heat and electricity?
Metals conduct electricity because the delocalised electrons are free to move throughout the structure, carrying electrical charge from one place to another when a potential difference is applied.
Metals conduct heat for a similar reason: the delocalised electrons gain kinetic energy near a heat source and move quickly through the structure, transferring energy to other electrons and ions throughout the metal.
In an exam answer, always name the delocalised electrons as the reason for conduction — 'metals conduct because they have electrons' alone will not gain full marks.
Section 3
Why can metals be bent and hammered into shape?
Metals are malleable (can be hammered into shape) and ductile (can be drawn into wires) because the atoms are arranged in layers. When a force is applied, these layers of positive ions can slide over each other without breaking the metallic bonds, because the delocalised electrons continue to hold the structure together as the layers move.
Students often say metals bend because the bonds 'break and reform' in a new position — the correct idea is that the layers of ions slide while the delocalised electrons keep bonding them together throughout.
Section 4
How strong is metallic bonding?
Metallic bonding involves strong electrostatic forces of attraction between the positive metal ions and the negatively charged delocalised electrons, acting in all directions throughout the giant structure. This strong attraction is why most metals have relatively high melting and boiling points, as a large amount of energy is needed to overcome it.
Think of the metal lattice as a set of fixed balls (the positive ions) sitting in a pool of water that can flow freely around them (the delocalised electrons) — the water still holds everything together even as the balls shift position.
Must Know
- Metals are giant structures of positive ions surrounded by a sea of delocalised electrons
- Metallic bonding = strong electrostatic attraction between positive ions and delocalised electrons
- Metals conduct electricity and heat because delocalised electrons are free to move through the structure
- Metals are malleable and ductile because layers of ions can slide over each other
- The delocalised electrons keep holding the structure together as the layers slide, so bonds don't break
That's the notes covered.
Carry on to the next subtopic.