What is Hydrogen bonding and how to classify it

In Hydrogen bonding, H atom is linked to a highly electronegative atom like F, O, N. Here, we will discuss the conditions, examples, types, effects of hydrogen bonding.

What is Hydrogen bonding and examples

  1. In H-bonding H atom is linked to a highly electronegative atom like F, O, N
  2. The electronegative atom attracts the shared electron pair towards itself. Hence, it carries the partial negative charge.
  3. Electropositive hydrogen atom in turn develops the partial positive charge.
  4. Negative end of one molecule attracts the other positive end of the molecule. This bond is called H-bonding
  5. H atom links to 2 electronegative atoms by a covalent bond and other by hydrogen bond.
  6. Example of H-bonding: H-X…….H-X……H-X like ……H-F…….H-F……H-F…….
  7. The strength of H-bonding is H….F > H…O > H…N
  8. Dotted line represents H-bonding. Solid line represents covalent bonding.

Conditions for H-bonding

  1. Molecule must contain a electronegative atom linked to H atom.
  2. Size of the electronegative atom should be small like F, N, O

Effects or consequences of H-bonding

H-bonding explains the abnormal physical properties in the molecules.

1. Higher melting and boiling points due to Hydrogen bonding

a) HF has the highest boiling point among HF, HCl, HBr, HI. [ H-F has highest strongest bonding ]

b) H2O is liquid due to H-bonding while H2S is gas [ H-bonding causes association of H2O molecule to raise the boiling point ]

c) C2H5OH has higher boiling point than diethyl ether [ H-bonding is present in C2H5OH ]

d) NH3 has higher boiling point than PH3. [ H-bonding is present in NH3 ]

e) Stronger H-bond is present in H-F than H2O. But H2O boils at higher temperature than HF. Because H2O molecule is linked to 4 other H2O molecules through H-bonds. But H-F molecule is linked to 2 other HF molecules through H-bonding.

2. Solubility due to H-bonding

Compounds which can form H-bond with the solvent molecule are water soluble.

For example lower alcohols are soluble in H2O.

Also NH3 is soluble in H2O because of H-bonding.

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