THOMSON's ATOMIC MODEL

The first simple model of an atom was proposed by J.J Thomson. According to Thomson, an atom is a positively charged uniform sphere of radius 10(minus 8) cm in which electrons are embedded in such a way that negative charge equals to positive charge. This model was also called plum-pudding model and water melon model.
This model was unable to explain the stability of an atom.

VOCABULARY(A)

ABDICATE : to give up power

SYNONYM : refusal from the power, renounce

ANTONYM : to gain power

The old king abdicated the throne.

VOCABULARY(A)

ABBREVIATE : to shorten

SYNONYM : to abridge, to curtail

ANTONYM : Lengthening, enhancing

The voluminous book was abbreviated for the convenience of the students.

DISTILLATION

This method is used for the purification of liquids which boils without decomposition and contain non-volatile impurities. e.g., pure water can be obtained from sea water by distillation, mixture of ether and toluene, benzene and aniline.

CRYSTALLISATION

This method is based the difference in the solubility of the various compound dissolved in a common solvent. e.g., a mixture of Potassium Nitrate and Sodium Chloride can be separated by this process.

PROPERTIES OF CATHODE RAYS

- Cathode rays always travel in straight line. Whenever an object is placed in the path of cathode rays, it casts a shadow on the walls opposite to the cathode.
- Cathode rays consist of material particles and produce mechanical effects.
- The beam of cathode rays are deflected towards the positively charged plate, hence the particles in the cathode rays carry negative charge.
- Cathode rays are also deflected from their path in magnetic field.
- Cathode rays penetrate the sheets of aluminium and other metals.
- The cathode rays produce X-rays when they strike metals with high melting point like tungsten.
- The cathode rays upon striking glass or certain other material cause them to glow.

DISTILLATION UNDER REDUCED PRESSURE

This process is used for those liquids which decomposes below their boiling point under reduced pressure, liquids boils at low temperature. Hence, the temperature for decomposition is not reached. Thus, this process is known as vacuum distillation e.g., glycerol can be separated by this method. It is also used for the concentration of sugar cane juice in sugar industry.