It occurs in compounds that have a hydrogen atom attached to one of the three most electronegative atoms of nitrogen, oxygen and fluorine, which must have an available lone pair of electrons. e.g. a –O-H -N-H F- H bond. There is a large electronegativity difference between the H and the O,N,F Hydrogen bonding Always show the lone pair of electrons on the O,F,N and the dipoles and all the δ – δ + charges
Hydrogen bonding occurs in addition to van der waals forces
Hydrogen bonding is stronger than the other two types of intermolecular bonding. The anomalously high boiling points of H2O, NH3 and HF are caused by the hydrogen bonding between the molecules The general increase in boiling point from H2S to H2Te is caused by increasing van der Waals forces between molecules due to an increasing number of electrons. Alcohols, carboxylic acids, proteins, amides all can form hydrogen bonds
18.104.22.168 Forces between molecules
Forces between molecules:
• hydrogen bonding.
The melting and boiling points of molecular substances are influenced by the strength of these intermolecular forces.
The importance of hydrogen bonding in the low density of ice and the anomalous boiling points of compounds.
Students should be able to:
• explain the existence of these forces between familiar and unfamiliar molecules
• explain how melting and boiling points are influenced by these intermolecular forces.