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CBSE Class 11th Chemistry Notes for Chapter 9 Hydrogen

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             UNIT 9 HYDROGEN


Hydrogen is the first element in the periodic table.

Its electronic configuration is 1s1.



Occurrence: Dihydrogen is the most abundant element in the universe. It is the principal element in the solar atmosphere.

Isotopes of hydrogen: Hydrogen has three isotopes: protium, deuterium and tritium



  1. Physical properties:
  • It is a colourless, odourless, tasteless, combustible gas.
  • It is lighter than air.
  • It is insoluble in water.
  1. Chemical properties
  • Reaction with halogens: It reacts with halogens to give hydrogen halides.
  • Reaction with dioxygen: It reacts with dioxygen to form water.
  • Reaction with dinitrogen: It reacts with dinitrogen to form ammonia.
  • Reaction with metals: It reacts with metals to yield the corresponding hydrides.
  • Reaction with metal ions and metal oxides: It reduces some metal ions in aqueous solution and oxides of metals (less active than iron) into corresponding metals.
  • Reaction with organic compounds: It reacts with organic compounds to give useful hydrogenated products.



  • The largest single use of dihydrogen is in the synthesis of ammonia which is used in the manufacture of nitric acid and nitrogenous fertilizers.
  • Dihydrogen is used in the manufacture of Vanaspati fat by the hydrogenation of polyunsaturated vegetable oils like soybean, cotton seeds, etc.
  • It is used in the manufacture of bulk organic chemicals, particularly methanol.
  • It is widely used for the manufacture of metal hydrides.
  • It is used for the preparation of hydrogen chloride, a highly useful chemical.
  • In metallurgical processes, it is used to reduce heavy metal oxides to metals.
  • Atomic hydrogen and oxy-hydrogen torches find use for cutting and welding purposes.
  • It is used as a rocket fuel in space research.
  • It is used in fuel cells for generating electrical energy.

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