CHEMISTRY · Single correct · A Level · Chemistry · Bonding · Bonding
Problem
In a diagram of NaCl(s), a student shows alternating Na⁺ and Cl⁻ ions, but the Na⁺–Cl⁻ distance is drawn noticeably shorter than the Cl⁻–Na⁺ distance in the same layer.
Which critique most accurately identifies the error in the student’s drawing?
(a) Because Na+ is smaller and attracts Cl− more strongly, the ions should be drawn closer together, so the unequal spacing is appropriate.
(b) The repulsion between like-charged ions is greater than the attraction between unlike charges, so larger gaps between consecutive Cl−–Na+ pairs are expected.
(c) Unequal spacing between consecutive unlike charges would create forces of different magnitudes and disrupt the periodic, energetically favorable lattice.
(d) Lattice energy depends only on the magnitudes of the ionic charges, so the exact center-to-center distances are not required to be equal.