When the 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 form a weak bond with a fluorine atom and this has occurred repeatedly among the HF molecule. This may be shown as:
H —— F……….. H —— F ………..
In other words, hydrogen atom acts as the 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 the 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:
- Due to hydrogen bonding, melting point and the boiling point of the substances become
- Due to hydrogen bonding, surface tension and viscosity rises.
- Due to hydrogen bonding, solubility increases.
Importance of hydrogen bonding:
- The vital substances for the living also dissolve in water inside the body by H-bonding and terry on metabolism.
- Protein and DNA from the helix structure by H-bonding.
- We can drink water due to hydrogen bonding among water molecules.