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Hydrogen Bonding

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Overview

The following topics are covered on this page :

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What is a Hydrogen Bond

Hydrogen bond as a result of polar moleculeNitrogen, oxygen and fluorine are highly electronegative elements. When they form a covalent bond with hydrogen atom, due to difference in electronegativity, dipoles are created where hydrogen atom acquires a partial positive charge and the electronegative atom acquires a partial negative charge. This partially positively charged hydrogen atom forms a weak bond with another highly electronegative atom nearby as depicted below :

Hydrogen bond

This weak bond, usually represented by dotted lines, is known as hydrogen bond.

Important Points Regarding H-Bond

Types of Hydrogen Bond

There are two types of hydrogen bonds.

  1. Intermolecular hydrogen bond
  2. Intramolecular hydrogen bond

Intermolecular hydrogen bond

Intermolecular hydrogen bond is formed between two different molecules of the same or different compounds.

Examples of intermolecular hydrogen bonding (different molecules of the same compound) : HF, R-OH (R is alkyl group), H2O etc.

Intermolecular hydrogen bond in hydrogen fluoride (HF)

Intermolecular hydrogen bonding in hydrogen fluoride (HF)

Intermolecular hydrogen bond in alcohol molecule

Intermolecular hydrogen bond in alcohol

Examples of intermolecular hydrogen bonding in different compounds : 'Water and alcohol' , 'Ammonia and water' etc.

Intermolecular hydrogen bond between ethanol and water

Intermolecular hydrogen bond between water and alcohol

Intramolecular hydrogen bond

Intramolecular hydrogen bond is formed when hydrogen atom is in between the two highly electronegative atoms present within the same molecule. Example : In salicylic acid, hydrogen is attached to one oxygen with a covalent bond and to other with intramolecular hydrogen bond.

Intramolecular hydrogen bonding in salicylic acid

Salicylic acid

Effects of Hydrogen Bond

Compounds that are capable of forming hydrogen bond tend to show abnormality in their physical properties. Some effects of hydrogen bond are given below :

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