4CH1

Covalent Bonding

Principles of Chemistry · 5 question types

Exam Frequency Analysis

Past paper frequency (2018 to 2024)

This topic accounts for approximately 8% of your exam marks.

stable

Low

Stable8%

Dot-and-cross diagrams and comparison of giant covalent vs simple molecular structures appear regularly.

A forms when two non-metal atoms share a pair of electrons
Each atom contributes one electron to the shared pair
The shared pair counts toward each atom's outer shell, so both atoms end up with a full (noble-gas) outer shell
Covalent bonds are very strong

The two shared electrons in a bond are the bonding electrons (or a bonding pair)
Outer-shell electrons that are not part of any bond are non-bonding electrons or

Exam tip

A near-every-paper question: what forces hold a covalent bond together?

Write: the (electrostatic) attraction between the shared pair of electrons and the two nuclei.

Watch out: say nuclei (plural), and name both the electrons and the nuclei. "Atoms sharing electrons" on its own scores nothing.

A single covalent bond is drawn as a short straight line between two atom symbols:
- H–H means a single bond between two hydrogen atoms
A double bond is drawn as two lines:
- O=O means a double bond
A triple bond is drawn as three lines:
- N≡N means a triple bond

In a covalent bond, electrons are shared. No atom permanently gains or loses an electron, and no ions form
In an ionic bond (Topic 6), electrons are transferred from one atom to another, and oppositely charged ions form

Every covalent substance falls into one of two structural classes:
- Simple molecular — small, discrete molecules (H₂O, O₂, CO₂); covered in section 3
- Giant covalent (also called macromolecules) — many millions of atoms covalently bonded into one continuous lattice (diamond, graphite); covered in section 4