Covalent bonding · Year 12
Non-metal atoms bond by sharing pairs of electrons. Each shared pair is a covalent bond, and sharing lets every atom fill its outer shell. Most covalent substances are made of small molecules such as water, ammonia and methane: the bonds inside each molecule are strong, but the forces between the molecules are weak.
Key facts
- A covalent bond is a shared pair of electrons between two non-metal atoms.
- An atom forms as many bonds as the electrons it needs to fill its outer shell: hydrogen 1, oxygen 2, nitrogen 3 and carbon 4.
- A double bond is two shared pairs (O=O, O=C=O); a triple bond is three (N≡N).
- Pairs of outer electrons that are not used in bonds are called lone pairs.
- Dot-and-cross diagrams show the outer electrons; displayed formulae show each bond as a line, like H–O–H.
- Simple molecular substances have low melting and boiling points and do not conduct electricity.