Pseudo-animation is particularly effective in illustrating the fractions of atoms that lie in the various unit cells. Structures of Ionic Solids describes simple ionic structures in terms of the packing of positive ions in holes in arrays of negative ions. In the course of the presentation, the features common to the packing of ions in binary ionic solids are described. Tetrahedral and octahedral holes are highlighted in closest packed arrays of anions. Then the coordinating anions are isolated and rotated to show their geometry.
Cubic holes appear in simple cubic arrays of anions.
Finally, the CsCl, CaF2, NaCl, TiO2, and cubic ZnS structures are built layer by layer using animation to show alternating layers of anions and cations and discuss the type and fraction of holes occupied. When appropriate, the relationship of alternate unit cells is described. Coordination numbers of cations and anions are highlighted and students are shown how to determine the numbers of ions in a unit cell. Pseudo-animation is particularly effective in illustrating the fractions of atoms that lie in the various unit cells. The relationships between the ionic radii and cell dimensions are developed.