Hydrogen Class 11 Notes - Chapter 9

The lightest atom is on earth is hydrogen which has a single electron. In the year 1766, Henry Cavendish was the first to discover it. The three stable isotopes of hydrogen are protium, deuterium, and tritium. The radioactive isotope amongst these three is tritium. Hydrogen is one of the most abundant elements found in the universe. Even though it resembles halogen and alkali metals, it has unique properties and has a separate position in the periodic table.

Water-Gas Shift Reaction

On an industrial scale level, Dihydrogen is prepared from petrochemicals by water-gas shift reaction. It is got in the form of byproduct on the electrolysis of brine.

Also Read: Preparation Of Hydrogen And Uses

Bond Dissociation Enthalpy

Dihydrogen has the highest H-H bond dissociation enthalpy for a single bond between the two atoms. The H-H bond dissociation enthalpy equals to 435.88 kJ mol–1

Read More: Bond Dissociation Enthalpy


Due to high negative dissociation enthalpy, dihydrogen is inactive at room temperature.  At suitable conditions, dihydrogen can combine with all the possible elements to form hydrides.

There are three different ways to categorize the hydride:

  • Saline or Ionic hydrides – Good reagent to prepare additional hydride compounds
  • Molecular or Covalent hydrides – Important for daily life. Example H2O
  • Non-stoichiometric or metallic hydrides – Used for ultra purification of dihydrogen

Read More: Hydrides



Important Questions

  1. How can you increase the production of dihydrogen from coal gasification?
  2. Explain auto-protolysis of water along with its significance.
  3. Explain the amphoteric nature of water with chemical reactions.
  4. Distinguish between hydration and hydrolysis.

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