In this post, I am sharing FSC 1st Year Chemistry Chapter 5 Atomic Structure Long Questions Notes PDF Download for the Students of Class 11. Students should also visit Chemistry Notes for Class 11 for complete 1st Year Chemistry Notes. To download 1st-year chemistry textbook click here.
1st Year English Notes are also available for the students of class 11.
Atomic Structure – 11th Class Chemistry Chapter 5 Long Questions PDF Download
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- 1st Year Chemistry Notes PDF Download
Introduction to the Chapter Atomic Structure
According to the Greek philosopher ‘Democritus,’ all the matter present in this universe is consist of very small particles called as atoms. Nothing is known more about atoms till the 18th century.
In 1808 an English School teacher ‘John Dalton’ put forward an atomic theory, according to which all the matter present in universe is composed of indivisible, tiny particles called as atoms of different elements which differ in their properties.
“John Dalton defined atom as the smallest particle of an element which cannot be broken down into simpler substances.”
The idea about the structure of the atom changed entirely at the end of the 19th century. Experiments on different elements revealed that the atom is not indivisible but it is composed of many small particles, e.g electrons, protons, neutrons, positrons, hyperons, neutrino, antineutrino, etc. Out of these particles, electrons, protons and neutrons are considered as the fundamental particles of an atom.
The experiments led to the discovery of these particles as discussed one by one.
GAS DISCHARGE TUBE EXPERIMENT
Discovery of Electrons
Gas discharge tube is a glass tube fitted with two metallic electrodes acting as cathode and anode. It is attached with a vacuum pump, so as to maintain the required pressure inside the experiment tube. The tube is filled with a gas, air or vapours of a substance at any desired pressure. The electrodes are connected to a source of high voltage. It was observed that current did not flow through the gas at Ordinary pressure even at a high voltage of 5000 volts. When the pressure inside the tube was reduced and a high voltage of 5000-10000 volts is applied, then an electric discharge took through the gas-producing a uniform glow inside the tube.
When the pressure was reduced further to about 0.01 torr, the original glow disappears, and some invisible rays were produced which produce fluorescence on the glass wall opposite to the cathode. These rays are called as cathode rays. The experiment is called the Gas discharge tube experiment.
DISCOVERY OF ELECTRONS
The rays produced in the gas discharge experiment are called as cathode rays, because they are produced at the cathode and travel opposite to the cathode. It is observed by the fluorescence produced on the glass. Many scientists work on these rays and study their properties. The important properties of cathode rays are explained as below.