IGCSE · Practice questions · Ions and ionic bonding

Transfer, then attract.

Six original Cambridge-style questions on ionic bonding: ions and their configurations, the formation of sodium chloride, dot-and-cross diagrams, formulae from charges, conductivity and melting points.

Original questions All questions on this page are original work, written in the Cambridge IGCSE style. They are not from past papers. They test the same concepts and skills the syllabus rewards.

Keep these straight

Metals lose, non-metals gain.

Metal atoms lose outer electrons to form positive ions.
Non-metal atoms gain electrons to form negative ions.
Balance the charges to find the formula.
Molten or aqueous: ions move and carry the current.

Recall

[2 marks]

State what is meant by an ion and by an ionic bond.

Ion: a charged particle formed when an atom (or group of atoms) loses or gains electrons. ✓
Ionic bond: the strong electrostatic attraction between oppositely charged ions. ✓

Explain

[3 marks]

Describe, in terms of electrons, how sodium chloride is formed from sodium atoms and chlorine atoms.

Each sodium atom (2,8,1) loses one electron to form Na⁺ (2,8). ✓
Each chlorine atom (2,8,7) gains that electron to form Cl⁻ (2,8,8). ✓
The oppositely charged ions attract each other strongly (ionic bonds). ✓

Analysis

[3 marks]

(Extended) Describe the dot-and-cross diagram for magnesium oxide. Include the configurations and charges of the ions formed.

Magnesium (2,8,2) transfers two electrons to oxygen (2,6); they are shown as two crosses in the oxygen's outer shell. ✓
Magnesium ion: [2,8] with charge 2+. ✓
Oxide ion: [2,8] with charge 2−; each ion drawn in square brackets with its charge outside. ✓

Analysis

[2 marks]

(Extended) Calcium forms Ca²⁺ ions and fluorine forms F⁻ ions. Deduce the formula of calcium fluoride and explain how the electrons are transferred.

Each calcium atom loses two electrons, one to each of two fluorine atoms. ✓
Two F⁻ ions balance one Ca²⁺ ion, so the formula is CaF₂. ✓

Explain

[3 marks]

Potassium bromide does not conduct electricity when solid but does conduct when molten or dissolved in water. Explain these observations.

Potassium bromide is made of ions (K⁺ and Br⁻). ✓
In the solid the ions are held in fixed positions and cannot move. ✓
When molten or in solution the ions are free to move and carry charge. ✓

Explain

[2 marks]

(Extended) Explain why magnesium oxide has a very high melting point.

Magnesium oxide is a giant ionic lattice with strong electrostatic attractions between many oppositely charged ions. ✓
A large amount of energy is needed to overcome these attractions. ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.