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Substances in Common Use

Preparation, Properties and Uses of Common Salt

Radioactive Elements

The elements that emit highly penetrating and high energy radiation beam are known as radioactive elements. The elements are subjected to spontaneous degeneration of nucleus along with the emission of radiations. Elements with the atomic number greater than 83 are considered as radioactive and some naturally occurring radioactive elements include uranium, radium and thorium.

Becquerel Rays

Becquerel rays are radiations given out by radioactive elements.


  • They are gas ionizers.

  • They affect photographic plate.

  • They can penetrate through matter.

  • They are affected by electric and magnetic fields.

Experiment to demonstrate the properties of Becquerel Rays

In this experiment, a lead cube was placed in a glass vessel and across its sides were placed two copper plates, connected to a very high d.c. potential. A photographic plate was placed over the cavity. The glass vessel was evacuated and then lead plug was removed.

It was found that the photographic plate developed the following pattern.

Alpha particles: By looking at the pattern, it was observed that the particles deflected towards the negative plate and having a dark spot are positive particles and are heavier than others.


  • It is similar to doubly ionised helium atom and has the speed of the order of 107 ms-1.
  • Alpha particles have large kinetic energy and momentum.
  • It strongly ionises the gas through which it passes.
  • It rapidly dissipates its energy as it moves through a medium and therefore its penetrating power is quite small.
  • As alpha particles are positively charged, so they are deflected by electric and magnetic fields.
  • Alpha particles cause fluorescence on striking a fluorescent material.

Beta particles: The particles deflected towards the positive plate and having a lighter spot are negative particles and are of medium mass.


  • These particles have speed of the order of 108 ms-1. Different beta particles emitted from same radioactive substance have different speed.
  • The rest mass of the beta particle is equal to the mass of an electron and charge on it is equal to the charge on an electron.
  • These particles ionise the gas through which they pass. Also, their ionising power is equal to 1/100 times that of the alpha particles.
  • Their penetrating power is more than the alpha particles.
  • As these particles are negatively charged, so they are deflected by electric and magnetic fields.
  • Beta particles cause fluorescence on striking a fluorescent material.

Gama particles: The particles which were not deflected towards any plate and having a very light spot are neutral particles and are of zero mass.


  • The speed of these particles is of the order of speed of light 3 ×108 ms-1
  • Their ionising power is very low and it is 1/1000 times that of the alpha particle.
  • Penetration power is very high for these particles.
  • As these particles have no charge on them, so they do not get deflected by electric and magnetic fields.
  • Gamma particles cause fluorescence on striking a fluorescent material.
  • Gamma radiations are very useful in the treatment of cancer.

We use soaps and detergents in our homes for almost all cleaning purposes. What are soaps and detergents? Soaps are sodium or potassium salts of higher fatty acids such as oleic acid (C17H33COOH), stearic acid (C17H35COOH), palimitic acid (C15H31COOH), etc. On the other hand, detergents are salts of higher sulphonic acids such as dedecylbenzenesulphonate (C18H30SO3Na).

Preparation of Soaps a…

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