Which of the following molecules would be expected to have a...

Which of the following molecules would be expected to have a dipole moment of zero because of symmetry?
a. $\mathrm{BeBr}_{2}$
b. $\mathrm{H}_{2} \mathrm{Se}$
c. $\mathrm{AsF}_{3}$
d. $\mathrm{SeF}_{6}$

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Key Concepts

Molecular Geometry

This concept involves the three-dimensional arrangement of atoms within a molecule. The geometry determines whether individual bond dipoles reinforce one another or cancel out, thereby influencing the overall polarity of the molecule.

Symmetry

Symmetry in a molecule indicates that its atoms are arranged in a balanced, orderly fashion, which often leads to the cancellation of dipole moments. In highly symmetric molecules, the vector sums of the bond dipoles cancel each other, resulting in a net dipole moment of zero.

Dipole Moment and Vector Addition

A dipole moment is a measure of the separation of positive and negative charges in a molecule. Since dipole moments have both magnitude and direction, the overall dipole moment is determined by vector addition of the individual bond dipoles. When molecular symmetry allows these vectors to cancel each other out, the molecule will exhibit no net dipole moment.

Bond Polarity

Bond polarity arises due to differences in electronegativity between bonded atoms, causing uneven sharing of electrons. However, even if bonds are polar, the overall molecular polarity may still be zero if the molecular geometry allows for complete cancellation of the individual bond dipoles through symmetry.

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