Ionic Bonding

5 marks · Easy

Ionic bonding depends on the strong attraction between oppositely charged ions. Magnesium oxide and aluminium oxide are two examples.

(a)

State the charge on the magnesium ion and on the oxide ion in magnesium oxide.

[1 mark]

(b)

Explain why the electrostatic attraction in magnesium oxide is stronger than in sodium chloride.

[2 marks]

(c)

Aluminium oxide has the formula . State the charge on the aluminium ion and the oxide ion.

[1 mark]

(d)

Calculate the total positive charge and the total negative charge present in one formula unit of .

[1 mark]

Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.

Show answer

(a) Mg2+ and O2-

(b) Because Mg2+ and O2- have higher charges than Na+ and Cl-, the electrostatic attraction between ions in magnesium oxide is stronger.

(d) Total positive charge: +6 (2 × 3+); total negative charge: -6 (3 × 2-)

Common mistakes: Confusing number of ions with charges; Incorrect multiplication of number of ions by charge

Show mark scheme and worked solution

Marking points

A1 (a) · 1 mark · Correctly identifies Mg2+ and O2-.

M1 (b) · 1 mark · States that MgO ions have higher charges than NaCl.

A2 (b) · 1 mark · Links higher charges to stronger electrostatic attraction.

A3 (c) · 1 mark · States charges on Al3+ and O2- correctly.

A4 (d) · 1 mark · Correct calculation of total positive (+6) and total negative (-6) charge in Al2O3.

Worked solution

a) Magnesium ion: Mg2+; oxide ion: O2-.

b) The electrostatic attraction in magnesium oxide is stronger than in sodium chloride because the ions in MgO carry greater charges (2+ and 2-) than in NaCl (1+ and 1-). Greater charges give stronger electrostatic forces.

c) Aluminium ion: Al3+; oxide ion: O2-.

d) In one formula unit of Al2O3: - Total positive charge: 2 × 3+ = +6 - Total negative charge: 3 × 2- = -6