Question

What is the distinction between a bond dipole and a molecular dipole moment?

Short answer

The distinction between a bond dipole and a molecular dipole moment lies in their scope and focus. A bond dipole moment refers specifically to the polarity of a single chemical bond between two atoms in a molecule, primarily determined by their electronegativity difference. In contrast, a molecular dipole moment represents the overall polarity of the entire molecule, determined by summing up the individual bond dipole moments and accounting for the molecular geometry.

Step-by-step solution

1. Definition of Bond Dipole Moment

A bond dipole moment is a measure of the polarity of a chemical bond between two atoms within a molecule. It is a vector quantity, which means it has both magnitude and direction. The bond dipole moment is determined by the difference in electronegativity between the two atoms forming the bond and the distance between them. When electrons are shared unequally between atoms, it results in a polar bond, with a positive and negative end (called a dipole). The dipole moment can be represented by an arrow pointing from the positive end to the negative end (from less electronegative to more electronegative atom).

2. Definition of Molecular Dipole Moment

A molecular dipole moment is the overall dipole moment for the entire molecule. It is a measure of the molecule's overall polarity and takes into consideration the bond dipoles of all the bonds in the molecule and the molecular geometry. To determine the molecular dipole moment, all the individual bond dipole moments in the molecule should be summed up, considering both their magnitudes and directions. The total vector sum of these bond dipoles will give the molecular dipole moment. For some molecules, bond dipoles may cancel each other due to their geometry, resulting in a nonpolar molecule with a net dipole moment of zero.

3. Distinction between Bond Dipole and Molecular Dipole Moments

The distinction between a bond dipole and a molecular dipole moment lies in the scope and focus of the concepts. A bond dipole moment refers specifically to the polarity of a single chemical bond between two atoms in a molecule, while a molecular dipole moment represents the overall polarity of the entire molecule. In summary, - Bond dipole moment: Polarity of a single chemical bond between two atoms within a molecule, it is primarily determined by the difference in electronegativity between these two atoms. - Molecular dipole moment: Overall polarity of the whole molecule, determined by summing up the bond dipole moments of all the individual bonds while taking into account the geometry of the molecule.