GCSE Chemistry Ionic Bonding Notes
Ionic bonding is the transfer of electrons from a metal to a non-metal. The ions formed attract each other strongly in a giant lattice.
Key concepts
- Ion formation
- Metals lose electrons to form positive ions (cations); non-metals gain electrons to form negative ions (anions).
- Electrostatic attraction
- Oppositely charged ions attract strongly in all directions, forming a giant ionic lattice.
- Dot-and-cross diagram
- Shows electron transfer using dots for one atom's electrons and crosses for the other's.
- Sodium loses 1 electron to become Na⁺; chlorine gains 1 to become Cl⁻.
- Group 1 form 1+ ions, Group 2 form 2+ ions, Group 6 form 2− ions, Group 7 form 1− ions.
- Ionic compounds are brittle because shifting layers bring like charges together, repelling and shattering the lattice.
Worked example
Describe what happens when sodium reacts with chlorine to form sodium chloride.
- 1Sodium has 1 outer electron; chlorine has 7 outer electrons.
- 2Sodium transfers its outer electron to chlorine.
- 3Sodium becomes Na⁺ (full outer shell); chlorine becomes Cl⁻ (full outer shell).
- 4The oppositely charged ions attract by strong electrostatic forces, forming NaCl.
Answer: An electron transfers from Na to Cl, forming Na⁺ and Cl⁻ ions held in a giant lattice by electrostatic forces.
Common mistakes
✗ Showing electrons being shared in an ionic bond.
✓ Ionic bonding is transfer, not sharing — sharing is covalent.
✗ Drawing all electron shells in a dot-and-cross diagram.
✓ Usually only the outer shell electrons are needed; check the question.
✗ Getting the charge sign wrong, e.g. writing Na⁻.
✓ Metals lose electrons so they are positive (Na⁺); non-metals gain electrons so they are negative (Cl⁻).
Quick check
Try these, then reveal the answers.
What charge does a magnesium ion have?Reveal answer
2+ (Mg²⁺)
Does ionic bonding involve sharing or transferring electrons?Reveal answer
Transferring electrons.
What ion does oxygen form?Reveal answer
O²⁻ (it gains 2 electrons).
Exam tips
- Use 'transfer' not 'share' for ionic bonding to avoid losing the mark.
- State the ion charges clearly with the correct sign and number, e.g. Mg²⁺ and O²⁻.
- Explain properties using the giant lattice and strong electrostatic forces.
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Frequently asked questions
How is an ionic bond formed?+
A metal atom transfers one or more electrons to a non-metal atom, forming oppositely charged ions that attract by strong electrostatic forces.
Why are ionic compounds brittle?+
When layers of the lattice shift, ions of the same charge line up and repel, causing the crystal to shatter.
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