Hydrogen is the simplest element. It is the first element in the periodic table, and it is placed in Group I of the periodic table.



Hydrogen is the lightest element and the most abundant element in the universe.

  • Hydrogen occurs naturally as a mixture of the three isotopes:
  • Protium, H,
  • Deuterium, D, (which is also called Heavy Hydrogen) and
  • Tritium, T.


Preparation of Hydrogen by the Action of Metals

The alkali metals, lithium, sodium, and potassium react violently with water at the ordinary temperature, yielding hydrogen.

2 Li + 2 H2O H2 + 2 LiOH

Calcium reacts with water more slowly unless the water is hot, when the action is more vigorous.

Ca + 2 H2O H2 + Ca(OH)2

Preparation of Hydrogen from Action of Acids

Hydrogen is prepared in the laboratory by the action of acids on metals.

Dilute sulphuric acid containing 1 volume of concentrated acid to 5 volumes of water, or dilute hydrochloric acid containing 1 volume of concentrated acid to 4 volumes of water, is added to granulated zinc.

Zinc sulphate or zinc chloride is formed in solution and the hydrogen that is evolved is collected over water in a trough.

Since hydrogen is very much lighter than air it may also be collected by upward displacement.


Before collecting hydrogen great care must be taken to ensure that all the air has been displaced from the apparatus since a mixture of hydrogen with air is highly explosive.


Hydrogen is;

  • a colourless odourless gaseous element,
  • sparingly soluble in water and the solubility is not much affected by change of temperature,
  • Does not support respiration although it is not poisonous. When hydrogen is breathed mixed with some air for a short time, it weakens the voice and raises its pitch,
  • a better conductor of heat than other gases, its conductivity being about five times that of air, and
  • Forms compounds with a large number of elements. In many cases, these compounds are formed by the direct combination of the elements.
  • Chemically, hydrogen reacts with most elements.

Hydrogen summary

Physical Properties

  • The lightest gas known.
  • Once used in airships but replaced by helium which is not explosive.
  • Used to make ammonia which is needed in the manufacture of fertilizers and explosives.

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