4.9.1 Cause of Formation of Hydrogen Bond

When hydrogen is bonded to strongly electronegative element ‘X’, the electron pair shared between the two atoms moves far away from hydrogen atom. As a result the hydrogen atom becomes highly electropositive with respect to the other atom ‘X’.

Since there is displacement of electrons towards X, the hydrogen acquires fractional positive charge (δ +) while ‘X’ attain fractional negative charge (δ–). This results in the formation of a polar molecule having electrostatic force of attraction which can be represented as :

H δ +   − X δ −   − − − H δ +   − X δ −   − − − H δ +   − X δ −

The magnitude of H-bonding depends on the physical state of the compound. It is maximum in the solid state and minimum in the gaseous state. Thus, the hydrogen bonds have strong influence on the structure and properties of the compounds.

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