Chapter 2 STRUCTURE OF THE ATOM – Class 9 Chemistry Notes

Chapter 2 STRUCTURE OF THE ATOM – 9th Class Chemistry Notes

 

Q#1) What is atom? Write in short words about history of atoms?

Answer: In 585 B.C, Ancient Greek philosopher Democritus suggested that matter is composed of tiny indivisible particles called atoms. The name ATOM was derived from the Latin word Atomos meaning indivisible.

Daltons Atomic Theory : In 1808 John Dalton put forward his Atomic Theory. According to this theory 1)All matter is made up of very small, indivisible particles called atoms. 2)Atoms of the same element s.are alike. 3)Atoms combine in different ways to form compound

PLUM PUDDING MODEL: Plum Pudding Model was put forwarded by J.J Thomson. According to this model Atoms were solid structures of positively charge with tiny negative particles stuck inside just like plums in the pudding.

For your information: J.J. Thomson (1856-1940) was a British physicist. He was awarded the 1906 Noble Prize in Physics for the discovery of electron and for his work on the conduction of electricity in gases.

Q#2 ) DISCUSS HOW CATHODE RAYS WERE DISCOVERED OR HOW ELECTRONS WERE DISCOVERED? OR DISCRIBE WORKING OF DISCHARGE TUBE? OR  WRITE NOTE ON CATHODE RAYS AND DISCOVERY OF ELECTRON? How was it proved that electrons are fundamental particles of an atom?

ANSWER: CATHODE RAYS EXPERIMENT: In 1895, Sir William Crooks performed experiments by passing electric current through gases in a discharge tube at a very low pressure. During this experiment crooks observed radiations , that were later named electrons.

J.J. Thomsan performed a large number of experiments and finally prove that electrons are basic particles of atom that are negatively charged and are responsible for all the chemical properties of the atom. So electrons are proved to be the fundamental particles of an atom.

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