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21 Chemistry -- Chemical Bonding and Shapes of Molecules

Why do compounds having hydrogen bonding have high melting and boiling points?

Why do compounds having hydrogen bonding have high melting and boiling points?


The compounds having hydrogen bonding show abnormally high melting and boiling points. The high melting and boiling point of the compound containing hydrogen bonds is due to the fact that some extra energy is needed to break these bonds.

·       The unusually high boiling point of hydrogen fluoride among the halogen acid is due to the existence of hydrogen bonding.

·       H2O is a liquid whereas H2S, H2Se and H2Te are all gases at ordinary temperature. In water, hydrogen bonding causes linkages in the water molecules which result in the boiling point of water is more than that of the other compounds.

·       Ammonia has a higher boiling point than PH3 because there is hydrogen bonding in NH3 but not in PH3.

·       Ethanol has a higher boiling point than diethyl ether because there is hydrogen bonding in the ethanol.


Compounds with hydrogen bonding tend to have higher melting and boiling points because the hydrogen bonding leads to stronger intermolecular forces. Intermolecular forces are the attractive forces between molecules, and they affect the physical properties of a substance, including melting and boiling points.

Hydrogen bonding is a particularly strong type of intermolecular force that occurs when a hydrogen atom is bonded to a highly electronegative atom such as nitrogen, oxygen, or fluorine. The electronegative atom attracts electrons in the bond towards itself, creating a partial negative charge on the electronegative atom and a partial positive charge on the hydrogen atom. These partial charges create a dipole, and the dipoles of neighboring molecules can attract each other through hydrogen bonding.

The hydrogen bonds are much stronger than the typical van der Waals forces, which are the intermolecular forces between non-polar molecules. This leads to a higher amount of energy required to break these bonds, which results in higher melting and boiling points for compounds with hydrogen bonding.

For example, water (H2O) has a boiling point of 100°C, which is much higher than the boiling point of a similar molecule like hydrogen sulfide (H2S), which has no hydrogen bonding and boils at -60°C. Similarly, ammonia (NH3) has a boiling point of -33°C, while its non-hydrogen bonded counterpart, phosphine (PH3), boils at -87°C. The difference in boiling points is due to the presence or absence of hydrogen bonding.

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