Welcome back Gobte — missed you this week. c) Step 1: Complete the table for coordination number and number of particles per unit cell. | Type of unit cell | Coordination number | Number of particles per unit cell | | :---------------------------- | :------------------ | :-------------------------------- | | Cubic close pack or face centered cubic | 12 | 4 | | Body centered cubic | 8 | 2 | d) i) Lattice energy is the energy change when one mole of an ionic compound is formed from its gaseous ions under standard conditions. It is a measure of the strength of the electrostatic forces between ions in a crystal lattice. ii) Born-Haber cycle for the formation of sodium oxide ($\text{Na}_2\text{O}$). The overall reaction is: $2\text{Na(s)} + \frac{1}{2}\text{O}_2(\text{g}) \rightarrow \text{Na}_2\text{O(s)}$ $$ \begin{array}{c} 2\text{Na(s)} + \frac{1}{2}\text{O}_2(\text{g}) \xrightarrow{\Delta H_f} \text{Na}_2\text{O(s)} \\ \downarrow 2\Delta H_{atom}(\text{Na}) \\ 2\text{Na(g)} + \frac{1}{2}\text{O}_2(\text{g}) \\ \downarrow \Delta H_{atom}(\text{O}) \\ 2\text{Na(g)} + \text{O(g)} \\ \downarrow 2IE_1(\text{Na}) \\ 2\text{Na}^+(\text{g}) + \text{O(g)} + 2\text{e}^- \\ \downarrow EA_1(\text{O}) \\ 2\text{Na}^+(\text{g}) + \text{O}^-(\text{g}) + \text{e}^- \\ \downarrow EA_2(\text{O}) \\ 2\text{Na}^+(\text{g}) + \text{O}^{2-}(\text{g}) \\ \downarrow U_L \\ \text{Na}_2\text{O(s)} \end{array} $$ iii) From the Born-Haber cycle, the expression for the lattice energy ($U_L$) of sodium oxide is: $$U_L = \Delta H_