Quick Notes Hydrogen Bonding

  • Hydrogen bonds are the strongest type of intermolecular force.
  • Hydrogen bonds exist between molecules that have a N-H, O-H or F-H bond.
    • Nitrogen, oxygen and fluorine are the most electronegative elements, so the covalent bonds between them and hydrogen are highly polar.
  • Highly polar bonds result in strong attractive forces between molecules.
    • The partially negative nitrogen, oxygen or fluorine forms hydrogen bonds with the partially positive hydrogen atoms from other molecules.
  • Substances that can form hydrogen bonds have higher melting points than similar-sized substances that cannot.

Full Notes Hydrogen Bonding

Hydrogen bonding is an intermolecular force that is a particular type of permanent dipole-dipole force.

Nitrogen, oxygen and fluorine are highly electronegative elements (see Electronegativity) whereas hydrogen has a very low electronegativity. When hydrogen covalently bonds with either nitrogen, oxygen or fluorine, the bond formed is highly polar.

hydrogen bond bonding intermolecular forces ammonia water

 

This high polarity gives rise to permanent dipole-dipole forces between the partially negative nitrogen, oxygen or fluorine atoms and the partially positive hydrogen atom. These forces are, relatively speaking, very strong and are called hydrogen bonds.

Hydrogen bonds only occur between molecules that contain nitrogen-hydrogen, oxygen-hydrogen or fluorine-hydrogen bonds.