Problem :

Using your knowledge of electronegativity, tell whether each of the following bonds will be ionic.

a. H-H
b. O-Cl
c. Na-F
d. C-N
e. Cs-F
f. Zn-Cl

Bonds are ionic when there is a large difference in electronegativities of the bonded atoms. Only c, e, and f are ionic.

Problem :

For each pair, indicate which bond will be stronger.

a. C-H, Li-F
b. Li-F, Mg-O
c. Li-F, Cs-I

a. Li-F is stronger because it is an ionic bond while C-H is a covalent bond.
b. Mg-O is stronger because Mg is charged 2+ and O is charged 2- while each ion in Li-F has only a charge of magnitude 1. Ions with higher charges are more strongly bound.
c. Li-F is stronger than Cs-I because the Li-F bond is far shorter than the Cs-I bond. By Coulomb's law, shorter ionic bonds should be stronger.

Problem :

Two ions of with charges +1 and -1 are separated by a distance of 1.0 angstroms. By what factor is the potential energy increased when those ions are moved to 4.0 angstroms away?

According to Coulomb's law, the energy should increase by a factor of 4.