Which of these have a dipole moment and how can you determine if they do? OF2, SOCl2, PBr4+ and PBr4-?

Answer 1

This is a question of electronegativity. As all molecules have differing identities of elemental makeup, all should have dipole moment...cept PBr4+ maybe.

Answer 2

A species will have a dipole moments if:
a) There are differences in electronegativity between the constituent atoms;
b) The molecule or ion is asymmetric.
BOTH conditions need to be satisfied.

All four species in the question satisfy condition (a). We therefore have to look at the shapes.

OF2: 8 valence electrons, 2 bonds, hence 2 lone pairs, hence non-linear, therefore OF2 WILL have a dipole moment.

SOCl2: 10 valence electrons, 4 bonds, hence 1 lone pair, hence pyramidal, therefore SOCl2 WILL have a dipole moment.

PBr4(+): 8 valence electrons, 4 bonds, hence no lone pairs, hence perfectly tetrahedral, therefore PBr4(+) will NOT have a dipole moment.

PBr4(-): 10 valence electrons, 4 bonds, hence 1 lone pair hence distorted tetrahedron, therefore PBr4(-) WILL have a dipole moment.

Answer 3

A DIPOLE MOMENT if the difference in the centres of gravity between the nuclei of all the atoms in a molecules and the electron cloud.
All four molecules will have a Dipole Moment, but it will be larger for some moleculles than others. This is becuase of molecular shape and the position of electronegative elements in the molecule
OF2 dp. = 0.67D (Debyes)
SOCl2 dp = 1.4 D
PBr4+ & PBr4- will have a d.p.simply because of the different electron numbers.