Question

The following compounds all display the NaCl structure. (i.e. They are isomorphous.) For each pair, indicate which would have the lattice energy of lesser magnitude. ROCI OKCI Sro Mgo CBao CSF Mgo Mgs Case Cas Consider how the relative energies of interaction of "point" charges would vary with respect to the expected interionic distances, according to Coulomb's Law. (Detailed calculations should NOT be required to make these comparisons -- but consider, for example, the relative effects of doubling the charges, as compared to increasing the interionic distances.)

Please show full work while solving

Answer 1

Lattice energy of a substance is directly proportional to the charge present on the ions and inversely proportional to the radii of the ions

Lattice energy is directly proportional to (Z+* Z-/ r+ *r - )

1. The lattice energy of KCl > RbCl. In this case, charges present on the ions are same and anion is same. Therefore, lattice energy depends on the radius only. but the the radius of Rb+ is greater than radius of K+

2. The lattice energy of MgO > SrO. In this case, charges present on the ions are same and anion is same. Therefore, lattice energy depends on the radius only. but the the radius of Sr2+ is greater than radius of Mg2+.

3..The lattice energy of BaO > CsF. In this case, charges present on the ions are DIFFERENT and anion are also different. Therefore, lattice energy depends on the radius as well as on the charge. The charge present on the ions of BaO is +2 and -2 whereas The charge present on the ions of CsF is +1 and -1.

4. The lattice energy of MgO > MgS. In this case, charges present on the ions are same and cation is same. Therefore, lattice energy depends on the radius only. but the the radius of S2- is greater than radius of O2-.

5.The lattice energy of CaS > CaSe. In this case, charges present on the ions are same and cation is same. Therefore, lattice energy depends on the radius only. but the the radius of Se2- is greater than radius of S2-.