Lesson 2.2 · AQA Combined Science

Ionic bonding: electrons transfer

Sodium chloride: follow one electron

A sodium atom has electrons arranged 2,8,1; chlorine has 2,8,7. Sodium transfers one electron to chlorine. Na⁺ is 2,8 and Cl⁻ is 2,8,8. Both now have full outer shells.

The ionic bond is the attraction

Electron transfer forms the ions. An ionic bond is the strong electrostatic attraction between oppositely charged ions. Do not stop your explanation at “electrons are transferred”.

Reading dot-and-cross diagrams

Dots and crosses show which atom electrons came from. They are all the same kind of particle. Put ions in square brackets, add their charges outside, and check the full outer shells. Na⁺ shows its new outer shell; the transferred electron is the cross on Cl⁻.

Magnesium oxide: two electrons move

Magnesium, 2,8,2, loses two electrons to form Mg²⁺, 2,8. Oxygen, 2,6, gains two to form O²⁻, 2,8. One magnesium atom supplies both electrons to one oxygen atom.

One metal ion can need two non-metal ions

In magnesium chloride, Mg loses two electrons, but each chlorine atom needs only one. Two chlorine atoms each gain one electron: one Mg²⁺ and two Cl⁻. These diagrams show ion formation; they are not balanced equations for reactions of the elements.

Remember

Transfer makes ions. Strong electrostatic attraction between opposite ions is the ionic bond.