GCSE Chemistry · AQA 8462 · Topic 4.2.1

Chemical bonds, ionic, covalent and metallic

Key points

Ionic bonding: a metal atom transfers electrons to a non-metal atom. Both form ions with full outer shells, e.g. $Na^+$ and $Cl^-$ . Ions are shown with dot and cross diagrams.
Group 1 metals form 1+ ions, Group 2 form 2+ ions, Group 6 non-metals form 2− ions and Group 7 form 1− ions.
An ionic compound is a giant lattice of oppositely charged ions held by strong electrostatic forces acting in all directions.
Covalent bonding: non-metal atoms share pairs of electrons. Examples are $H_2$ , $Cl_2$ , $HCl$ , $H_2O$ , $NH_3$ , $CH_4$ , $O_2$ and $N_2$ .
Covalent substances can be small molecules, giant covalent structures or very large molecules such as polymers.
Metallic bonding: a regular arrangement of positive metal ions surrounded by delocalised electrons, which are shared through the structure.
Each type of diagram (dot and cross, ball and stick, 2D and 3D) has limitations, e.g. it may not show relative sizes or the 3D shape.

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Atoms bond to reach a more stable electron arrangement, usually a full outer shell. The type of bond depends on which kinds of atom are involved: metal and non-metal, two non-metals, or metal atoms on their own.

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