To melt an ionic solid, energy must be supplied to disrupt the forces between ions so the regular array of ions collapses. Predict (and explain) how the melting point is expected to vary as a function of the distance between cation and anion.

Examine the trends in lattice energy in the table below. The value of the lattice energy becomes somewhat more negative on going from NaI to NaBr to NaCl, and all are in the range from -700 to -800 kJ/mol. Propose a reason for the observation that the lattice energy of ${NaF}\left(\Delta_{\text {lattice }} U=-926 {~kJ} / {mol}\right)$ is much more negative than those of the other sodium halides.

Lattice Energies of Some Ionic Compounds

$$\begin{array}{l|r} \hline \text { Compound } & \begin{array}{r} \Delta_{\text {lattice }} U \\ (\mathrm{~kJ} / \mathrm{mol}) \end{array} \\ \hline \mathrm{LiF} & -1037 \\ \hline \mathrm{LiCl} & -852 \\ \hline \mathrm{LiBr} & -815 \\ \hline \mathrm{Lil} & -761 \\ \hline \mathrm{NaF} & -926 \\ \hline \mathrm{NaCl} & -786 \\ \hline \mathrm{NaBr} & -752 \\ \hline \mathrm{Nal} & -702 \\ \hline \mathrm{KF} & -821 \\ \hline \mathrm{KCl} & -717 \\ \mathrm{KBr} & -689 \\ \mathrm{KI} & -649 \\ \hline \end{array}$$

Predict the trend in lattice energy, from least negative to most negative, for the following compounds based on the ion charges and ionic radii: LiI, LiF, CaO, RbI.

A unit cell of cesium chloride is illustrated in Figure 12.8. The density of the solid is 3.99 g/cm$^3$, and the radius of the Cl$^−$ ion is 181 pm. Calculate the radius of the Cs$^+$ ion in the center of the cell. (Assume that the Cs$^+$ ion touches all of the corner Cl$^−$ ions.)

Based on a C-C distance of 139 pm, determine the side-to-side dimension of a planar, ${C}_6$ ring.

Determine how many tin atoms are contained in the tetragonal crystal lattice unit cell of $\beta$-tin. How many tin atoms are contained in the cubic crystal lattice unit cell of $\alpha$-tin?

What mass of lithium can be acquired from 73 million metric tons of lithium carbonate? (1 metric ton = 1000 kg.)

What is a heritable trait ? ______________________________

BLAST is a computational tool used by genome biologists to:

a. assemble short overlapping DNA sequences into long contiguous DNA sequences called contigs.

b. compare a given DNA or protein sequence to all other DNA or protein sequences in a database.

c. align genetic maps based on recombination frequencies to physical maps of chromosomes.

d. identify sites in the DNA where restriction endonucleases cut.

e. disassemble genomic DNA sequences into small segments.

What is the $\ce{pOH}$ of a $0.025\ce{ M}$ solution of $\ce{H+}$ ions?

Some ions do not have a corresponding neutral atom that has the same electron configuration. For each of the following ions, identify the neutral atom that has the same number of electrons and determine if this atom has the same electron configuration.

$$Cl^-$$

The ionic radii of the ions $\mathrm{S}^{2-}, \mathrm{Cl}^{-}$, and $\mathrm{K}^{+}$ are 184, 181, 138 pm respectively. Explain why these ions have different sizes even though they contain the same number of electrons.

Write the electron configuration for the monatomic ions formed from the following elements (which form the greatest concentration of monatomic ions in seawater): (a) Cl (b) Na (c) Mg (d) Ca (e) K (f) Br (g) Sr (h) F

How many moles of ammonium ions are in 6.955 g of ammonium carbonate?