Ionic and covalent bonding: how atoms join, with examples
Compare ionic and covalent bonding, write ionic formulae and explain properties such as melting point and electrical conductivity.
GCSEA-LevelHigh SchoolAPCurriculum fit: GCSE Chemistry and Combined Science (bonding, structure and the properties of matter). US: high school physical science (chemical bonding); also AP Chemistry.
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What is it?
Atoms bond to get a full outer shell of electrons. In ionic bonding, a metal atom transfers electrons to a non-metal atom, forming oppositely charged ions that attract each other. In covalent bonding, non-metal atoms share pairs of electrons.
The type of bonding explains properties such as melting point and electrical conductivity.
Key formulas and ideas
- Ionic compound: metal + non-metal, with a giant lattice of ions.
- Covalent compound: non-metal atoms sharing electrons, usually small molecules.
- Ionic compounds conduct when molten or dissolved, because their ions can move.
- Simple covalent substances have low melting points and do not conduct electricity.
Worked examples
Example 1: Ionic bond
Question: Describe how sodium chloride forms.
- Sodium (2, 8, 1) loses one electron to form Na⁺.
- Chlorine (2, 8, 7) gains one electron to form Cl⁻.
- The oppositely charged ions attract strongly.
Answer: Electron transfer forms Na⁺ and Cl⁻ ions held together in a lattice
Example 2: Formula of an ionic compound
Question: Work out the formula of calcium chloride (Ca²⁺ and Cl⁻).
- Ca²⁺ has a charge of 2+, Cl⁻ has 1−.
- Two chloride ions are needed to balance one calcium ion.
Answer: CaCl₂
Example 3: Explain a property
Question: Why does water (H₂O) have a low melting point compared with sodium chloride?
- Water is a simple covalent molecule with weak forces between molecules.
- Little energy is needed to separate the molecules, unlike the strong ionic bonds in sodium chloride.
Answer: Weak intermolecular forces need little energy to overcome
Common mistakes
- Saying covalent bonds break when a molecular substance melts. Only the weak forces between molecules are overcome.
- Writing an ionic formula without balancing charges.
- Saying solid ionic compounds conduct.
- Calling an ionic lattice a 'molecule'.
Practice questions
Frequently asked questions
How can I tell which type of bond a compound has?
A metal bonded to a non-metal is usually ionic. Two or more non-metals are usually covalent.
What is a metallic bond?
The attraction between positive metal ions and a sea of delocalised electrons, which explains why metals conduct and can be shaped.
Related guides
Electron configuration (electronic structure) and ions
Write electron shell diagrams for the first 20 elements and work out the charges of ions, with worked examples and practice questions.
GCSEHigh SchoolElectrolysis explained: products at each electrode
See how electricity splits ionic compounds, and predict the products at the anode and cathode for molten and aqueous solutions.
GCSEA-LevelHigh SchoolStates of matter: solids, liquids, gases and changes of state
Use the particle model to explain melting, boiling and condensing, and why temperature stays constant during a change of state.
KS3GCSEMiddle SchoolHigh SchoolSources and review
Reviewed by StudyMorrow editorial review on 5 Nov 2026.