Define hydrogen bonding - QS Study
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When hydrogen atom is bonded to the atoms of highly electro-negative elements such as fluorine, oxygen or nitrogen, the hydrogen atoms form a weak bond with the electro-negative atom of the other molecule. This weak bond is called hydrogen bond.

For example in hydrogen fluoride, HF, hydrogen atoms forms a weak bond with fluorine atom and this is occurred repeatedly among the HF molecule. This may be shown as:

H ——  F……….. H —— F ………..

In other words, hydrogen atom acts as bridge between two atoms, holding one atom by a covalent bond and the other atom by a hydrogen bond. The hydrogen bond is represented by dotted line (………) while the covalent bond is represented by the solid line (——). As a result of hydrogen bonding, HF exist as a cluster of hydrogen fluoride molecules and is represented as (HF)n

Thus the attractive force which binds hydrogen atom of one molecule with electro-negative atom (F, O or N) of another molecule is known as hydrogen bond or hydrogen bonding.

Influence of hydrogen bonding on the physical properties:

  1. Due to hydrogen bonding, melting point and boiling point of the substances become
  2. Due to hydrogen bonding, surface tension and viscosity rises.
  3. Due to hydrogen bonding, solubility increases.

Importance of hydrogen bonding:

  1. The vital substances for living also dissolve in water inside the body by H-bonding and terry on metabolism.
  2. Protein and DNA form the helix structure by H-bonding.
  3. We can drink water due to hydrogen bonding among water molecules.