Question

How would we differentiate graphite, bromine, hydrogen fluoride, lithium fluoride, and hydrogen bromide?

Answer 1

Well, `"carbon (graphite)"`, and `"lithium fluoride"` are non-molecular materials.

Explanation:

Graphite is a network covalent solid, and lithium fluoride is an ionic solid. Neither substance is molecular, and these would be expected to exhibit exceptionally high melting and boiling points, which reflects the strength of the interparticle bond.

On the other hand, `Br_2`, `HBr`, and `HF` are all molecular species, containing discrete molecules held together by intermolecular forces. For elemental bromine, the elemental forces are relatively weak dispersion forces, nevertheless, the physical size of the electron cloud around the bromine molecule results in a normal boiling point of `59` `""^@C`.

Hydrogen fluoride features hydrogen bound to a highly electronegative fluorine, and results in an elevated boiling point of `19.5` `""^@C`; as with water, the phenomenon of hydrogen bonding is a potent intermolecular force. For `HBr` the strength of intermolecular bonding would not be so pronounced given the reduced electronegativity of `Br`, and a boiling point of `-66.8` `""^@C` is reported.