How do intermolecular forces affect solvation?

1 Answer

Polar molecules dissolve in polar solvents (ex. water) and non-polar molecules will dissolve in non-polar solvents (ex. hexane).

The type of forces that exist between neighboring molecules will be determined by the properties of those molecules.

Polar molecules will be attracted to each other by either hydrogen bonding or dipole-dipole interactions. These intermolecular forces are made possible by a large difference in electronegativity values for two atoms bonded to each other.

In water, the electronegativity difference between oxygen (3.5) and hydrogen(2.1) is 1.4 (3.5-2.1=1.4). This, and waters bent shape, make water a polar molecule. Another polar molecules is ammonia (NH3), whose trigonal pyramidal shape and electronegativity different in N-H bonds of 0.9 make this substance soluble in water.

Non-polar molecules are attracted to each other by London forces (dispersion) and either do not have dipoles (ex. CH4), or they have multiple dipoles which cancel each other out due to their geometry (CO2 is nonpolar because its linear shape makes the molecule nonpolar due to the two dipoles O=C=O canceling each other out).