Giant ionic structures
2 marks · EasyExplain why the melting point of sodium oxide (Na_2O) is higher than that of sodium chloride (NaCl).
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
Stronger electrostatic attractions between ions in Na_2O due to greater charge on the oxide ion than the chloride ion, so more energy needed to break the bonds.
Must show: Charge on O^{2-} ion, Greater ionic attraction, Higher energy required
Also accept: Oxide ion is 2- whilst chloride ion is 1-
Common mistakes: Linked to number of atoms but not charge
Show mark scheme and worked solution
Marking points
M1 · 1 mark · Identifies that oxide ion has greater charge than chloride ion
A1 · 1 mark · Relates greater charge to stronger forces (and thus higher melting point)
Worked solution
The oxide ion (O^{2-}) has a greater charge than the chloride ion (Cl^-).
This causes stronger electrostatic attractions between the Na^+ and O^{2-} ions than between Na^+ and Cl^-.
More energy is needed to break the stronger forces in Na_2O, so its melting point is higher.