Hydrogen bonds

A Hydrogen Bond is an attraction between a Hydrogen atom and an atom of Nitrogen, Oxygen or Flourine. It exists in polar compounds, a common example of this being water where the interaction exists between the Oxygen and Hydrogen. Hydrogen bonds can exists as intermolecular attractions, where the bonding exists between different molecules, or intramolecular, where the bond exists between different parts of the same molecule.

A hydrogen bond is a stronger attraction than Van der Waals forces and other polar-polar attractions but not as strong as ionic or covalent bonding. Evidence for Hydrogen bonding can be found when comparing the boiling points of hydrogen molecules across groups 5,6 and 7 of the periodic table. The compounds where hydrogen bonding is present produce a much higher boiling point as Hydrogen bonds require more energy to be broken than Van der Waals forces.

References:

http://www.chemguide.co.uk/atoms/bonding/hbond.html

http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/H/HydrogenBonds.html