Four one-dimensional representations of an AB ionic solid are described below. In each description, “A” is the cation and “B” is the anion; all ions are shown with equal radii.
I. …ABABABAB… with equal spacing between every adjacent pair
II. …AABB AABB… with equal spacing throughout
III. …ABABABAB… but the A–A distance is one-half the A–B distance
IV. …AB AB AB… (a vacant B site every fourth position)
Which representation most strongly violates the requirement that like-charged ions be kept as far apart as possible within the lattice?
a) III
b) II
c) IV
d) I