Ionic bonding in magnesium oxide
5 marks · HardThis question is about the ionic bonding in magnesium oxide (MgO).
State which ions are present in magnesium oxide and what charges they carry.
Explain in detail why there is a strong electrostatic force between these ions.
Suggest, with a reason, how the strength of ionic bonding in magnesium oxide would change if the oxide ions were replaced by fluoride ions (F^-).
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(a) Mg^{2+} and O^{2-} ions are present. · must show Mg^{2+} ion, O^{2-} ion, Correct charges
(b) There is a strong electrostatic attraction because Mg^{2+} ions are positively charged and O^{2-} ions are negatively charged. The force is strong because both ions have a charge of 2, leading to a larger force between them. · must show Oppositely charged ions attract, Reference to double charges (2+ and 2-) increasing strength
(c) The ionic bonding would be weaker with fluoride ions because F^- has only a 1- charge, compared to O^{2-}'s 2- charge. Lower charges mean weaker electrostatic attraction. · must show Bonding gets weaker, Less charge on F^- than O^{2-}, Reference to weaker attraction
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Marking points
B1 (a) · 1 mark · States both Mg^{2+} and O^{2-} ions present, with correct charges.
M1 (b) · 1 mark · Mentions attraction between oppositely charged ions (electrostatic force).
A1 (b) · 1 mark · Gives reason: both ions carry double charges (2+ and 2-), increasing strength.
M2 (c) · 1 mark · States the bonding would be weaker with fluoride ions.
A2 (c) · 1 mark · Explains that weaker bonding is due to F^- having a smaller charge (1-) than O^{2-}, leading to weaker force.
Worked solution
(a) The ions present in magnesium oxide are Mg^{2+} and O^{2-}.
(b) Strong electrostatic attraction exists because Mg^{2+} ions (positive) and O^{2-} ions (negative) attract each other. Because both carry charges of 2, the force is stronger than for ions with lower charges.
(c) If the oxide ions were replaced by fluoride ions (F^-), the ionic bonding would be weaker. This is because the F^- ion has only a 1- charge, so the attraction between Mg^{2+} and F^- is weaker than between Mg^{2+} and O^{2-}.