Hydrogen bond

Hydrogen bonding takes place when a single hydrogen atom binds to either a nitrogen, flourine or oxygen atom (which are very electronegative). Since hydrogen has a single lone electron, and nitrogen, flourine and oxygen atoms require extra electrons to have a full outer shell, this electron is drawn away to the electronegative atom, leaving hydrogen with only a proton in its nucleus. The hydrogen atom now has a positive charge (due to the absence of the electron and the presence of a proton) and it is this proton that is attracted to a pair of non-bonding electrons from the electronegative atom (nitrogen, oxygen or flourine). This bond is stronger than Van der Waals' forces and basic dipole:dipole forces.