Which of the following molecules have net dipole moments?...

Which of the following molecules have net dipole moments? For the molecules that are polar, indicate the polarity of each bond and the direction of the net dipole moment of the molecule. a. $\mathrm{CH}_{2} \mathrm{Cl}_{2}, \mathrm{CHCl}_{3}, \mathrm{CCl}_{4}$ b. $\mathrm{CO}_{2}, \mathrm{N}_{2} \mathrm{O}$ c. $\mathrm{PH}_{3}, \mathrm{NH}_{3}$

Which of the following molecules have net dipole moments? For the molecules that are polar, indicate the polarity of each bond and the direction of the net dipole moment of the molecule.
a. $\mathrm{CH}_{2} \mathrm{Cl}_{2}, \mathrm{CHCl}_{3}, \mathrm{CCl}_{4}$
b. $\mathrm{CO}_{2}, \mathrm{N}_{2} \mathrm{O}$
c. $\mathrm{PH}_{3}, \mathrm{NH}_{3}$

Key Concepts

Molecular Geometry

Molecular geometry refers to the three?dimensional arrangement of atoms in a molecule. This arrangement is critical because it affects how individual bond dipoles (vectors representing the difference in electronegativity between bonded atoms) combine. If the geometry is symmetrical, the bond dipoles may cancel out, leading to no net dipole moment, whereas an asymmetrical distribution results in a net dipole moment.

Electronegativity

Electronegativity is the measure of an atom's ability to attract shared electrons in a bond. Differences in electronegativity between atoms create polar bonds with partial positive and negative charges. The magnitude and direction of these bond dipoles are determined by the differences in electronegativity, influencing the overall polarity of the molecule.

Bond Dipole

A bond dipole is a vector quantity that represents the separation of electrical charge within a chemical bond due to the difference in electronegativity of the two atoms. Its magnitude depends on the charge difference, and its direction is from the less electronegative atom toward the more electronegative atom. Bond dipoles are the building blocks that, when added vectorially, determine the net dipole moment of a molecule.

Symmetry and Dipole Cancellation

Symmetry involves the spatial arrangement of bonds in a molecule. In molecules with high symmetry, individual bond dipoles may cancel each other out, leading to a nonpolar molecule. Conversely, in molecules with lower symmetry or with substituents that disturb the symmetrical arrangement, the bond dipoles do not fully cancel, resulting in a net dipole moment.

Polarity of Molecules

Molecular polarity is a measure of the separation of positive and negative charges within a molecule. It arises when there is an uneven distribution of electron density due to differences in electronegativity and an asymmetrical molecular geometry. The overall polarity is determined by the vector sum of all bond dipoles, which can either cancel out in nonpolar molecules or add up to produce a net dipole moment in polar molecules.

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