Ionic compounds NaF and MgO each consist of a 1:1 ratio of cations to anions
CHEMISTRY · Single correct · A Level · Chemistry · Thermodynamics · Thermodynamics
Problem
Ionic compounds NaF and MgO each consist of a 1:1 ratio of cations to anions. Which statement most accurately predicts how the depth of the potential-energy well for a single Mg2+–O2− ion pair compares with that for a Na+–F− ion pair?
(a) The Mg^{2+}–O^{2-} well is shallower because the higher ionic charges cause the ions to repel each other more strongly, offsetting attraction.
(b) The Mg^{2+}–O^{2-} well is deeper because the product of ionic charges is larger while the ionic radii are of similar magnitude.
(c) The Na^{+}–F^{-} well is deeper because the small F^{-} ion allows the ions to approach more closely, outweighing the lower charges.
(d) The Mg^{2+}–O^{2-} well is shallower because the larger O^{2-} ion increases the internuclear distance, reducing electrostatic attraction.