NCERT Class 11 Chemistry Structure of Atom

Read and download NCERT Class 11 Chemistry Structure of Atom chapter in NCERT book for Class 11 Chemistry. You can download latest NCERT eBooks for 2021 chapter wise in PDF format free from This Chemistry textbook for Class 11 is designed by NCERT and is very useful for students. Please also refer to the NCERT solutions for Class 11 Chemistry to understand the answers of the exercise questions given at the end of this chapter

Structure Of Atom Class 11 Chemistry NCERT

Class 11 Chemistry students should refer to the following NCERT Book chapter Structure Of Atom in standard 11. This NCERT Book for Grade 11 Chemistry will be very useful for exams and help you to score good marks

Structure Of Atom NCERT Class 11


The existence of atoms has been proposed since the time of early Indian and Greek philosophers (400 B.C.) who were of the view that atoms are the fundamental building blocks of matter. According to them, the continued subdivisions of matter would ultimately yield atoms which would not be further divisible. The word ‘atom’ has been derived from the Greek word ‘a-tomio’ which means ‘uncutable’ or ‘non-divisible’. These earlier ideas were mere speculations and there was no way to test them experimentally. These ideas remained dormant for a very long time and were revived again by scientists in the nineteenth century.

The atomic theory of matter was first proposed on a firm scientific basis by John Dalton, a British school teacher in 1808. His theory, called Dalton’s atomic theory, regarded the atom as the ultimate particle of matter (Unit 1).

In this unit we start with the experimental observations made by scientists towards the end of nineteenth and beginning of twentieth century. These established that atoms can be further divided into subatomic particles, i.e., electrons, protons and neutrons— a concept very different from that of Dalton. The major problems before the scientists at that time were:  to account for the stability of atom after the discovery of sub-atomic particles, to compare the behaviour of one element from other in terms of both physical and chemical properties, · to explain the formation of different kinds of molecules by the combination of different atoms and, to understand the origin and nature of the characteristics of electromagnetic radiation absorbed or emitted by atoms.


Dalton’s atomic theory was able to explain the law of conservation of mass, law of constant composition and law of multiple proportion very successfully. However, it failed to explain the results of many experiments, for example, it was known that substances like glass or ebonite when rubbed with silk or fur generate electricity. Many different kinds of sub-atomic particles were discovered in the twentieth century. However, in this section we will talk about only two particles, namely electron and proton.

2.1.1 Discovery of Electron

In 1830, Michael Faraday showed that if electricity is passed through a solution of an electrolyte, chemical reactions occurred at the electrodes, which resulted in the liberation and deposition of matter at the electrodes. He formulated certain laws which you will study in class XII. These results suggested the particulate nature of electricity.

An insight into the structure of atom was

obtained from the experiments on electrical discharge through gases. Before we discuss these results we need to keep in mind a basic rule regarding the behaviour of charged particles : “Like charges repel each other and unlike charges attract each other”.

In mid 1850s many scientists mainly Faraday began to study electrical discharge in partially evacuated tubes, known as cathode ray discharge tubes. It is depicted in Fig. 2.1. A cathode ray tube is made of glass containing two thin pieces of metal, called electrodes, sealed in it. The electrical discharge through the gases could be observed only at very low pressures and at very high voltages.

The pressure of different gases could be adjusted by evacuation. When sufficiently high voltage is applied across the electrodes, current starts flowing through a stream of particles moving in the tube from the negative electrode (cathode) to the positive electrode (anode). These were called cathode rays or cathode ray particles. The flow of current from cathode to anode was further checked by making a hole in the anode and coating the tube behind anode with phosphorescent material zinc sulphide. When these rays, after passing through anode, strike the zinc sulphide coating, a bright spot on the coating is developed(same thing happens in a television set) 

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Chapter 1 Some Basic Concepts of Chemistry
NCERT Class 11 Chemistry Some Basic Concepts Of Chemistry
Chapter 2 Structure of Atom
NCERT Class 11 Chemistry Structure of Atom
Chapter 3 Classification of Elements and Periodicity in Properties
NCERT Class 11 Chemistry Classification of Elements and Periodicity In Properties
Chapter 4 Chemical Bonding and Molecular Structure
NCERT Class 11 Chemistry Chemical Bonding and Molecular Structure
Chapter 5 States of Matter
NCERT Class 11 Chemistry State Of Matter
Chapter 6 Thermodynamics
NCERT Class 11 Chemistry Thermodynamics
Chapter 7 Equilibrium
NCERT Class 11 Chemistry Equilibrium
Chapter 8 Redox Reactions
NCERT Class 11 Chemistry Redox Reactions
Chapter 9 Hydrogen
NCERT Class 11 Chemistry Hydrogen
Chapter 10 The s-Block Elements
NCERT Class 11 Chemistry The s Block Elements
Chapter 11 The p-Block Elements
NCERT Class 11 Chemistry The p Block Elements
Chapter 12 Organic Chemistry – Some Basic Principles & Techniques
NCERT Class 11 Chemistry Organic Chemistry Some Basic Priciples and Techniques
Chapter 13 Hydrocarbons
NCERT Class 11 Chemistry Hydrocarbons
Chapter 14 Environmental Chemistry
NCERT Class 11 Chemistry Environmental Chemistry
Other Chapters
NCERT Class 11 Chemistry Lab Manual ph and ph change in Aqueous Solutions
NCERT Class 11 Chemistry Lab Manual Purification and Criteria of Purity
NCERT Class 11 Chemistry Lab Manual Systematics Qualitative Analysis
NCERT Class 11 Chemistry Lab Manual Basic Laboratory Techniques
NCERT Class 11 Chemistry Lab Manual Titrimetric Analysis
NCERT Class 11 Chemistry Lab Manual Chemical Equilibrium Ionic Equilibrium
NCERT Class 11 Chemistry Lab Manual Information about Investigatory Projects
NCERT Class 11 Chemistry Lab Manual Introduction
Part I Answer to Some Selected Problems
NCERT Class 11 Chemistry Answer of Some Selected Problems
Part I Appendices
NCERT Class 11 Chemistry Appendix 2 Elements Their Atomic Number and Molar Mass
NCERT Class 11 Chemistry Appendix 3
NCERT Class 11 Chemistry Appendix 4 Physical Constants
NCERT Class 11 Chemistry Appendix 5 Some Useful Conversion Factores
NCERT Class 11 Chemistry Appendix 6 Thernodynamic Data at 298 K
NCERT Class 11 Chemistry Appendix 7 Standard Potentials at 298 K in Electrochemical order
NCERT Class 11 Chemistry Appendix 1
Part II Answer to Some Selected Problems
NCERT Class 11 Chemistry Answer to Some Selected Problems

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