Compounds are made up of individual atoms that bond together. However, bonds are not the only thing that binds things. Solids, liquids and gases are all examples of intermolecular forces, that is, a force of attraction between molecules. There are many types of intermolecular forces and some are discussed here.
Sometimes when compounds are formed, a phenomenon wherein one end of the molecular configuration is more negative than the other end happens. This results into a partial polarity that makes the molecule a dipole. As what Coulomb says, like poles repel and unlike poles attract. The inherent polarity of this dipole will cause it to be attracted to the opposite pole of another dipole molecule. This is called dipole-dipole interaction.
On the other hand, even nonpolar molecules can experience some intermolecular forces, by chance at the very least. Since electrons are freely-moving around the atomic center, there is a chance that these electrons stay a bit too long in a single place, that a temporary pole is formed. With this, an attraction is formed albeit very weak since the polarity is momentary. These are called London forces. These kind of forces, explain why nonpolar molecules have very low boiling points. Water is a combination of two hydrogen atoms and one oxygen atom. The hydrogen is bonded to a highly-electronegative atom, oxygen. This makes the hydrogen be very attracted to highly-electronegative atoms in nearby molecules. This attraction is called hydrogen bonding. This weak electrostatic attraction between the more positive H portion and negative charge clouds of a lone pair of a highly-electronegative atom is the main reason why water has a high boiling point. Furthermore, hydrogen bond is stronger than London and dipole-dipole interaction.
Posted 2010-12-14 and updated on Dec 14, 2010 6:10am by crisd