Consider the ionic compounds KF, NaCl, NaBr, and LiCl. (a) Use ionic radii (Figure 7.8) to estim

Consider the ionic compounds KF, NaCl, NaBr, and LiCl. (a)...

Consider the ionic compounds $\mathrm{KF}, \mathrm{NaCl}, \mathrm{NaBr}$, and $\mathrm{LiCl}$. (a) Use ionic radii (Figure 7.8) to estimate the cation-anion distance for each compound. (b) Based on your answer to part (a), arrange these four compounds in order of decreasing lattice energy. (c) Check your predictions in part (b) with the experimental values of lattice energy from Table 8.1. Are the predictions from ionic radii correct?

Key Concepts

Theoretical Versus Experimental Comparison

Comparing theoretically predicted values of lattice energy, based on ionic radii and interionic distances, with experimental data is important for validating the approximations and assumptions used in the theoretical models. This process highlights the interplay between simple models and real-world measurements, often revealing additional factors that influence the properties of ionic compounds.

Cation-Anion Distance Estimation

The distance between a cation and an anion in an ionic compound is typically estimated by summing their ionic radii. This estimation is crucial because the lattice energy is highly sensitive to the separation distance; smaller distances usually lead to stronger attractions and thus greater lattice energy.

Ionic Radii

Ionic radii describe the effective sizes of ions in a crystal lattice. They are fundamental to understanding how ions pack together and determine the distances between the centers of adjacent cations and anions. The radii are used to estimate the bond distances, which in turn affect many physical properties of ionic compounds.

Lattice Energy

Lattice energy is the energy released when gaseous ions come together to form an ionic solid, or the energy required to separate the ions in the solid into gaseous ions. It is a measure of the strength of the ionic bonds in a crystal lattice and depends heavily on the magnitudes of the ionic charges and the distances between the ions.

Coulomb's Law in Ionic Compounds

Coulomb's law explains the electrostatic forces between charged particles by stating that the force is directly proportional to the product of the charges and inversely proportional to the square of the distance between them. In the context of ionic compounds, this relationship helps explain why smaller interionic distances (which occur with smaller ionic radii) result in stronger attractive forces and higher lattice energies.

Transcript

00:01 There are four ionic compounds, kf, n -s -e -l, n -a -b -r, and lithium chloride.

00:05 We have to use ionic radii from figure 7 .8 to estimate the cat -ion -an -ion distance for each compound, and then based on that distance, we have to arrange these four compounds in order of decreasing lattice energy.

00:22 Then we have to check our predictions in part b with the experimental value of lattice energy from table 8 .1 and are the predictions from ionic radia correct or incorrect we have to explain that first let me find the catarine anion distance from the data in figure 7 .8 for k a plus ionic radius is 152 p .m and fluoride minus is 100.

01:00 19 p .m.

01:02 Picometer.

01:03 So it is 271 picometer.

01:08 For any cl, any plus ion is 116 p .m.

01:14 Plus cl minus ion 167 p .m.

01:20 Together it is 283 p .m.

01:24 Cation anion.

01:25 Distance.

01:25 For any br, sodium ion, 116 p .m.

01:33 Plus 182 p .m.

01:36 For the anicadi of bromine.

01:41 So in case of nabr cat aneur dstan anand distance is 298 p .m.