Question

(a) Based on the lattice energies of MgCh, and SrCl given in table 8.1, what is the range of values that you would expect for the lattice energy of CaCI,?

Answer 1

The lattice energy of
`C_aCl_2` is expected to fall between that of
`MgCl_2`, which would be higher due to its smaller cation size, and
`SrCl_2`, which would be lower due to its larger cation size. Charge and ionic radius directly influence lattice energy, with higher charges and smaller radii leading to greater lattice energies.

A student has inquired about the expected range of values for the lattice energy of
`C_aCl_2` based on the lattice energies of
`MgCl_2` and
`SrCl_2`. Considering periodic trends and the fact that as you move down the group in the periodic table, the cations increase in size, we can expect the lattice energy to decrease due to the larger ionic radii. Since
`Mg^{2+` is smaller than Ca2+ and Ca2+ is smaller than
`Sr^{2+`, and assuming that the lattice energies of
`MgCl_2` and
`SrCl_2` are known, the lattice energy of
`C_aCl_2` should be between those values. The lattice energy large for
`MgCl_2` would be higher than that for
`C_aCl_2`, and the lattice energy for
`SrCl_2` would be the lowest of the three due to its largest ionic radius among the cations.

Valence electron configuration plays a significant role in determining the lattice energy, as ions with higher charges typically result in larger lattice energies, provided that the ionic radii are comparable. For instance, a cation with a +2 charge will tend to have a greater lattice energy when paired with a chloride than a cation with a +1 charge, given similar ionic sizes.