Molecular Dipole Moment (College Board AP® Chemistry) : Study Guide

Molecular Dipole Moment

• Molecular dipole moments give information about the separation of charges in a molecule

• The dipole moment (?) is a measure of the net polarity in a molecule and is measured in Debyes (D)

  • It is a product of the charge, Q, at the end of a dipole and the distance, r, between the charge

• The greater the difference in electronegativity between the bonded atoms of the molecule, the greater the dipole moment of that molecule

• For example, in chloromethane, the C—Cl bond has a dipole moment because chlorine is more electronegative than carbon

  • The chlorine atom develops a partial negative (δ^-) charge

  • The carbon atom develops a partial positive charge (δ⁺)

  • Therefore, the C—Cl bond is described as a polar bond

• The dipole moment in the molecule is represented using an arrow with a plus at the end

  • The plus end of the arrow represents the positive atom or end of the polar bond / dipole moment

  • The arrowhead represents the negative atom or end of the polar bond / dipole moment

Molecular Dipole Moment

A dipole moment exists between C-Cl bonds due to the large difference in electronegativity between the carbon and chlorine atoms.