2. Atomic Structure

Ionic/covalent Crystals — Quiz

Test your understanding of ionic/covalent crystals with 5 practice questions.

Practice Questions

Question 1

Using the Coulomb approximation $U\propto\frac{z_+z_-}{r_++r_-}$, compare the lattice energies of CaO and MgO by calculating the ratio $U_{\mathrm{CaO}}/U_{\mathrm{MgO}}$ given $r_{\mathrm{Ca}^{2+}}=0.100\,\mathrm{nm}$, $r_{\mathrm{Mg}^{2+}}=0.072\,\mathrm{nm}$, and $r_{\mathrm{O}^{2-}}=0.140\,\mathrm{nm}$.

Question 2

For an ideal hexagonal close-packed (HCP) crystal with atomic radius $r$ and ideal $c/a=\sqrt{8/3}$, derive an expression for the volume $V_c$ of the conventional hexagonal unit cell in terms of $r$.

Question 3

Given that diamond crystallizes in a cubic unit cell with lattice parameter $a=3.57\times10^{-10}\,\mathrm{m}$, contains $Z=8$ atoms per cell, and has molar mass $M=12.01\,\mathrm{g/mol}$, calculate its theoretical density $\rho$ in $\mathrm{g/cm^3}$ (use $N_A=6.022\times10^{23}\,\mathrm{mol^{-1}}$).

Question 4

In ionic solids at moderate temperatures, which diffusion mechanism predominates for cation migration?

Question 5

According to the radius-ratio rule, a small-to-large ionic radius ratio $r_\mathrm{small}/r_\mathrm{large}=0.225$ predicts which coordination geometry?