Two alkali-metal chlorides—NaCl and CsCl—crystallize in similar structures
CHEMISTRY · Multi-part · AP · Chemistry · Compound Structure and Properties · Compound Structure and Properties
Problem
Two alkali-metal chlorides—NaCl and CsCl—crystallize in similar structures. The crystal radii of the cations are given below.
Ion | Crystal radius / pm
Na⁺ | 102
Cs⁺ | 167
The chloride ion radius is 181 pm in both lattices.
Answer the following questions about the relative strength of ionic interactions in these two salts.
(a) Identify which compound, NaCl or CsCl, exhibits the stronger ionic interaction. Support your claim with qualitative reasoning.
(b) On fully-labeled axes, sketch qualitative potential-energy curves (potential energy on the vertical axis, internuclear distance on the horizontal axis) for NaCl and CsCl on the same set of axes. Your sketch should clearly show any differences in both well depth and equilibrium separation distance.
(c) Based on your sketch in part (b), predict which salt requires more energy to vaporize one mole of the crystal into gaseous ions. Explain your prediction.