I've a problem with ranking compounds

Question

thank you for taking some time for this, these two questions i dont get:

arrange the following bonds in order of polarity, from the least polar to the most polar: H-H, O-H, Cl-H, S-H, and F-H

Rank the following ionic compounds in order of lattice energy, from the least exothermic (least negative lattice enthalpy) to the most exothermic (most negative lattice enthalpy): BaO, NaF, MgO, CsBr

thank you!!

Answer 1

The bond polarity is a function of the difference in electronegativity (EN) of the rwo atoms. Obviously, in H-H there is 0 difference so it is not polar at all. Since fluorine is the most electronegative element, the H-F is the most polar bond of the group. Cl-H would be next , and so on. Just look at the EN differences and rank them.

The lattice energy increases as the radii of the ions decreases and as the charge increases. So look at radii (they increase going from right to left and from top to bottom in the periodic table). Then consider charge (e.g. 2+ is stronger than 1+)