Chemical BondingOxford AQA IGCSE Chemistry: Revision notes
Section 1
What are compounds and why do atoms bond?
A compound is a substance in which atoms of two or more different elements are chemically combined.
Atoms bond because most atoms do not have a full outer (highest occupied) energy level, which is an unstable arrangement. By transferring or sharing electrons in their highest occupied energy levels, atoms can achieve the stable electron arrangement of a noble gas (a full outer shell).
This process of gaining a stable electron arrangement drives the formation of chemical bonds.
Section 2
What is ionic bonding?
Ionic bonding involves the transfer of electrons from a metal atom to a non-metal atom.
- The metal atom loses electrons and becomes a positively charged ion
- The non-metal atom gains those electrons and becomes a negatively charged ion
- Both ions end up with the stable electron arrangement of a noble gas
The oppositely charged ions are then held together by strong electrostatic forces of attraction.
Section 3
What is covalent bonding?
Covalent bonding involves the sharing of pairs of electrons between atoms, usually between two non-metal atoms.
Each atom contributes one electron to a shared pair, and this shared pair counts towards the outer shell of both atoms, helping each achieve a stable, noble-gas electron arrangement.
Covalent bonding forms individual molecules, such as small simple molecules or, in some cases, giant covalent structures.
Section 4
What is metallic bonding?
Metallic bonding occurs in metals and involves delocalised electrons.
Metal atoms are arranged in a giant regular lattice of positive ions. The electrons in the highest occupied energy levels become delocalised — free to move throughout the whole structure rather than staying attached to one atom.
Strong electrostatic attractions between the positive metal ions and the sea of delocalised electrons hold the metallic structure together.
Section 5
How do you tell ionic, covalent and metallic bonding apart?
| Bond type | What happens to electrons | Typical elements involved |
|---|---|---|
| Ionic | Transferred (given away by one atom, taken by another) | Metal + non-metal |
| Covalent | Shared between atoms | Non-metal + non-metal |
| Metallic | Delocalised (free to move through the structure) | Metal atoms only |
When asked to identify the type of bonding in a substance, first check whether it contains a metal, a non-metal, or only metal atoms — this immediately tells you whether the bonding is ionic, covalent or metallic.
Must Know
- Compounds contain atoms of two or more elements chemically combined
- All three types of bonding involve atoms achieving the electron arrangement of a noble gas
- Ionic bonding: electrons transferred, forming oppositely charged ions (metal + non-metal)
- Covalent bonding: electrons shared between atoms (non-metal + non-metal)
- Metallic bonding: delocalised electrons free to move through a lattice of positive metal ions
- The type of bonding present can usually be predicted from whether the elements involved are metals or non-metals
That's the notes covered.
Carry on to the next subtopic.