Hydrogen and S-Block Element: Properties, Structure and Hydrides (For CBSE, ICSE, IAS, NET, NRA 2022)

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  • Hydrogen peroxide is a colorless syrupy liquid and has sharp odours.
  • It has boiling point of .
  • It is miscible in all proportions with water, alcohol and ether.

Oxiding Properties

Oxidizing Action in Acid Solution

Oxidizing Action in Alkaline Solution

Reducing Properties

Reducing Action in Acid Solution

Reducing Action in Alkaline Solution


  • Hydrogen peroxide is used for bleaching hair, leather and wool etc.
  • Hydrogen peroxide is used as a germicide and disinfectant.
  • Hydrogen peroxide is used as an explosive when mixed with alcohol.
  • Hydrogen peroxide is used in the preparation of foam rubber.
  • Hydrogen peroxide is used in pollution control e. g. treatment of drainage and sewage water for dichlorination.


The Lewis structure and molecular structure of hydrogen peroxide are shown below:

The Lewis Structure


Ionic Hydrides

  • Group l and 2 metals are sufficiently electropositive to force the hydrogen atom to accept an electron and form ionic hydrides.
  • These hydrides are white crystalline solids and are formed by heating the metal in hydrogen at temperatures up to .

Covalent Hydrides

  • This type of hydrides are formed from elements of Group 13 to Group 17 in the Periodic Table.
  • The stability of the hydrides of the elements of a particular periodic group decreases with increasing atomic number. Thus, hydrogen chloride is stable to heat while hydrogen iodide is easily decomposed into its elements.

Interstitial Hydrides

  • These compounds formed by a number of transition metals in which hydrogen is accommodated in the lattice of the transition element.
  • No definite chemical formula can be allocated to these substances, i.e.. they are non-stoichiometric.

Hydrogen as a Fuel

  • Scientist made effort hydrogen gas as a method of obtaining alternative energy source.
  • Hydrogen gas could replace gasoline to power automobiles or be used with oxygen gas in fuel cells to generate electricity.
  • Major advantage of using hydrogen gas is that it is a pollution free because the end product in a hydrogen-powered engine or in a fuel cell would be water.

S-Block Elements

  • The s-block elements have an outer electronic configuration ns1or ns2 and are placed in the group 1 and 2 of the periodic table.
  • The elements lithium, sodium, potassium, rubidium, cesium and francium belong to group 1 and are known as alkali metal.
  • The elements beryllium, magnesium, calcium, strontium, barium and radium belong to group 2 and are known as alkaline earth metals.

Occurrence of Alkali Metals

  • Sodium is found as sodium chloride in the sea water and as sodium nitrate (Chile saltpeter) in the deserts of Chile.
  • Potassium is found in sea water, and also as carnallite .
  • Lithium, rubidium and cesium occur in a few rare aluminosilicates.
  • Francium is radioactive its longest-lived isotope .

Electronic Configuration

The alkali metals with their symbols, atomic numbers and electronic configurations are listed in table:

Electronic Configuration of Alkali Metals

Electronic Configuration of Alkali Metals

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