(a) In the textbook Sodium and Chlorine are listed as having ionic radii of 0.98 and 1.81 Å respectively. NaCl can form a face-centered cubic unit cell. What is the lattice constant of such a unit cell?
(b) Now we assume two ions Na+ and Cl- in space. Using equations 2.1 and 2.2 in the book to describe how the electrostatic forces between the two ions vary with their distance seems to imply the two ions will collide with each other. However, due to the repulsion of the inner shell electrons of the ions, this cannot be the case. We can assume that the energy of repulsion E between the two ions can be described by: E = D0(R0/a)12 [D0=0.376 kcal/mole; R0= 3.547 Å]
The equation 2.1 is F_c=-K/a^2 equation 2.2 is K=(k_0)(qZ_1)*(qZ_2)
Using the above equation and equations 2.1 and 2.2 what is the equilibrium distance between the sodium and chlorine ions?
(c) What might account for the differences between the equilibrium distance predicted in part b versus the actual distance between the ions?