Question

(a) Which type of intermolecular attractive force operates between all molecules? (b) Which type of intermolecular attractive force operates only between polar molecules? (c) Which type of intermolecular attractive force operates only between the hydrogen atom of a polar bond and a nearby small electronegative atom?

Short answer

(a) The type of intermolecular attractive force that operates between all molecules is the London dispersion force. (b) The type of intermolecular attractive force that operates between polar molecules is the dipole-dipole force. (c) The type of intermolecular attractive force that operates only between the hydrogen atom of a polar bond and a nearby small electronegative atom is called hydrogen bonding.

Step-by-step solution

(a) Intermolecular attractive force between all molecules

The type of intermolecular attractive force that operates between all molecules is the London dispersion force. These forces result from the temporary dipoles that arise due to the random movement of electrons in the electron cloud around a molecule. London dispersion forces can affect all types of molecules (polar and non-polar) and are the weakest of the intermolecular forces, but become stronger as the size of the molecule increases.

(b) Intermolecular attractive force between polar molecules

The type of intermolecular attractive force that operates between polar molecules is the dipole-dipole force. This force occurs when the positive end of one polar molecule is attracted to the negative end of another polar molecule. As a result, there is an electrostatic attraction between the two dipoles. Dipole-dipole forces are stronger than London dispersion forces but are still weaker than hydrogen bonding.

(c) Intermolecular attractive force between specific polar molecules

The type of intermolecular attractive force that operates only between the hydrogen atom of a polar bond and a nearby small electronegative atom is called hydrogen bonding. This force is a particularly strong type of dipole-dipole interaction that occurs when hydrogen is bonded to a highly electronegative atom (such as nitrogen, oxygen, or fluorine). The electronegative atom pulls electron density away from the hydrogen, creating a strong dipole. This positive hydrogen then forms an attraction with a lone pair of electrons on a nearby electronegative atom. Hydrogen bonding is the strongest of the three types of intermolecular forces mentioned here.