AQA Chemistry (8462) 4.2.1.2 · Process
Ionic bonding
A soft metal and a poisonous gas become the salt on your chips. Where do the electrons go, and what actually holds the salt together?
Triple Science · Foundation tier
Start here
Hot sodium, a jar of chlorine, a flash of yellow light.
Drop hot sodium into chlorine gas and it burns with a bright yellow flame. When the smoke clears, the jar is coated in white crystals of sodium chloride. A sodium atom has one electron in its outer shell. A chlorine atom has seven.
Commit first
Where does sodium's single outer electron end up?
A full outer shell is stable: that is why the noble gases barely react. Sodium (2.8.1) is one electron past a full shell; chlorine (2.8.7) is one short. When a metal meets a non-metal, the metal atom loses its outer electrons and the non-metal atom gains them. For Groups 1, 2, 6 and 7, both end up with the electron arrangement of a noble gas. Neither is an atom any more: each is an ion, a particle with a charge. Watch it happen, one step at a time, and call each step before you see it.
Worked · call each step
Sodium and chlorine
Before · two neutral atoms, crosses for Na, dots for Cl
Step 1 of 3 · Which atom will lose electrons?
The charge on an ion comes from counting electrons. A Group 1 metal loses one, so it becomes 1+. Group 2 loses two: 2+. A Group 7 non-metal gains one: 1−. Group 6 gains two: 2−. The ions are held by strong electrostatic forces acting in every direction, which is why ionic compounds are giant lattices, not pairs. Now draw one yourself.
Your turn · draw the dot-and-cross diagram
Move the electrons. Label the charges. Then check it.
Metal electrons are crosses, non-metal electrons are dots. An exam diagram earns its marks for three things: the right electrons moved, a full outer shell on each ion, and the charge written on each bracket.
Electrons moved
Formula forge
Balance aluminium oxide
0 of 3 balanced
Worked for you: aluminium forms Al³⁺, oxide is O²⁻. The lowest total both charges reach is 6, so two Al³⁺ (6+) balance three O²⁻ (6−). Press Next compound when you have read it.
Ions in the box
2 × Al³⁺ 3 × O²⁻
Charge meter
Net charge 0
Balanced at zero. Formula: Al₂O₃. 2 × 3+ = 6+, and 3 × 2− = 6−. The subscripts come from balancing the charges, not from the group numbers.
Command words in this lesson
- Describe
- Say what happens, in order. No reason needed.
- Explain
- Say why. Link each step to the next with “so” or “because”.
- Deduce
- Work it out from what you are given. Here: from the group numbers.
- Draw
- Marks are for content, not art: electrons, brackets, charges.
Key fact
Electron transfer makes the ions. The ionic bond is the strong electrostatic attraction between the oppositely charged ions, and the charges always balance to zero.
Examiner tip
Key note · AQA 4.2.1.2 (8462)
Ionic bonding
- Ionic bonding happens between a metal and a non-metal.
- The metal atom loses its outer electrons and becomes a positive ion.
- The non-metal atom gains them and becomes a negative ion. Both now have full outer shells.
- Group 1 → 1+, Group 2 → 2+, Group 6 → 2−, Group 7 → 1−.
- The ionic bond is the strong electrostatic attraction between the oppositely charged ions.
- The charges balance, so the compound has no overall charge: MgCl₂, Al₂O₃.
Photograph this card. Tomorrow, cover it and say each line first.
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Ask Mr Badmus AI
Not sure which way the electrons go, or how many?
Dot-and-cross figures show every shell, with the metal's electrons as crosses and the non-metal's as dots. Real ions do not sit in neat pairs: each is surrounded on all sides by ions of the opposite charge in a giant lattice. GCSE draws only compounds of Group 1 and 2 metals with Group 6 and 7 non-metals; the forge adds nitride and aluminium ions for charge-balancing practice only.