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NCERT Class 11 Chemistry Chapter 2 Notes Structure of Atom - Download PDF

NCERT Class 11 Chemistry Chapter 2 Notes Structure of Atom - Download PDF

Edited By Sumit Saini | Updated on Mar 19, 2024 04:51 PM IST

The structure of the atom is an important chapter in the Class 11 Chemistry subject. The understanding of the atom and its structure is very important for chemistry students. Structure of Atom Class 11 notes helps students to get the basic information about atoms. Structure of Atom class 11 notes act as a quick revision tool for students appearing for the examination. It will also boost their memory power.

class 11 chemistry chapter 2 notes also help to crack the NEET, JEE Main, etc. examinations. cbse class 11 chemistry ch 2 notes help students in getting high marks in the board examination. For quick revision students can go through chemistry class 11 chapter 2 notes pdf .

Also, students can refer,

NCERT Notes for Class 11 Chemistry Chapter 2

NCERT Notes for Class 11 Chemistry Chapter 2: Topic 1

Structure of Atom

Discovery of electron discharge tube experiment

In the discharge tube experiment conducted by William Crookes, the conduction of electricity through gases at low pressure is studied. The discharge tube is a cylindrical hard glass tub about 60 cm in length. Both ends of the discharge are to be sealed and fitted with the two metal electrodes.

Only at very low pressure and high voltages electric discharge through the gases is observed. The pressure of a gas can be adjusted by using evacuation. Under the supply of high voltage across the electrodes current starts flowing and the stream of particles are moving from the tuber in the negative electrode to the positive electrode. And it is called cathode rays.

NCERT Notes for Class 11 Chemistry Chapter 2: Topic 2

Properties of Cathode Rays

  • They travel in a straight line.

  • Cathode rays begin from the cathode and then move towards the anode.

  • They are invisible but can be made visible with the help of materials like a fluorescent or a Phosphorescent.

  • Since under the supply of electric charge they are moved to the positive charge which indicates that cathode rays consist of negatively charged particles.

  • The properties of cathode rays do not depend upon the material of the electrode in which it is used and the nature of gases that are present in the cathode ray tube.

NCERT Notes for Class 11 Chemistry Chapter 2: Topic 3

Determination of Charge by Mass Ratio for Electrons.

Experimentally JJ Thomson determined the charge-to-mass ratio of the electrons. According to Thomson’s experiment, the amount of deviation for a particle from their path under the presence of an electric and a magnetic field depends upon

  • Deflection tends to be higher when the magnitude of the charge is higher for the particles.

  • When the mass of a particle is lighter the deflection will be greater.

  • With the increase of voltage across the electrodes for with the increase of the strength of the magnetic field the deflection of electrons will also rise.

Thomson determined the value of eme=1.758820×1011Ckg-1

Where a mass of the electron and is the magnitude of charge.

NCERT Notes for Class 11 Chemistry Chapter 2: Topic 4

Charge on the Electron

Oil drop experiment conducted by R A Milliken finds out the charge on the electron.

Charge of an electron=-1.6022×10-19C

Mass of electronee/me=1.6022×10-19C/1.758820×1011Ckg-1=9.1094×10-31kg

NCERT Notes for Class 11 Chemistry Chapter 2: Topic 5

Discovery of Proton Anode Rays

Goldstein conducted another experiment with the help of a perforated cathode ray tube. A new type of eraser passes through the perforation of the card order by reducing the pressure and it is moving just the opposite direction as that of the cathode rays. These are named canal rays or anode rays.

Properties of anode rays

  • The magnitude of the positive charge of anode rays depends upon the nature of the gas that is present in the tube.

  • It also depends on the gas for the value charge to mass ratio.

  • The behavior of anode rays is just opposite to the cathode rays and the magnetic and electric field.

NCERT Notes for Class 11 Chemistry Chapter 2: Topic 6

Thomson Model of The Atom

JJ Thomson proposed a structure for an atom that can be regarded as a sphere of an approximate radius carrying a positive charge due to protons and in which the negatively charged electrons are embedded into it. Thereby the atom can be visualized as a pudding for a cake positively charged with electrons in it. And the mass of atoms evenly spread over the atom. Although it was able to explain the overall neutrality of the other it cannot explain the result of the scattering experiment conducted by Rutherford.


JJ Thomson's model of atom

NCERT Notes for Class 11 Chemistry Chapter 2: Topic 7

Rutherford Alpha Particle Scattering Experiment

By the use of a thin foil of metals like gold silver platinum with a beam of fast-moving Alpha particles Rutherford conducted some scattering experiments. And the thin gold foil has a fluorescent screen surrounding it. Whenever a particle struck the screen a flash of light was produced.


Rutherford alpha particle scattering experiment

One of the characteristics of the Rutherford Alpha scattering experiment is,

  • Most of the Alpha particles do not undergo any deflection only a few of them undergo deflection through some small angles.

  • Only a few deflectors back.

Based on these observations Rutherford concluded that since most of the Alpha particles passed through the foil without taking place any deflection there is much space in the atom. Since only a small question underwent deflection so the positive charger is a very small volume concentrated at the center. And the small portion of the atom is named the nucleus.

NCERT Notes for Class 11 Chemistry Chapter 2; Topic 8

Atomic Number

The number of protons present in the nucleus is referred to as the atomic number. For example, the number of protons in a sodium atom is 11 and also the atomic number of sodium is 11. For maintaining electrical neutrality the number of electrons in an atom is equal to the number of protons.

NCERT Notes for Class 11 Chemistry Chapter 2: Topic 9

Mass Number

The sum of the number of protons and neutrons present in a nucleus together is called the mass number.

NCERT Notes for Class 11 Chemistry Chapter 2: Topic 10

Isotopes and Isobars

The element that is having the same atomic number but the different mass number is isotopes. 1H1, 1H2, 1H3. And the element that is processing the same mass number but the different atomic number is isobars. 6C14, 7N14.

NCERT Notes for Class 11 Chemistry Chapter 2: Topic 11

Development Leading to Bohr's Model of The Atom

  • Radiation causes wavelike and particle-like properties which means that it is having a dual character

  • The atomic spectra can be explained only by assuming the quantum state electronic energy levels in atoms.

NCERT Notes for Class 11 Chemistry Chapter 2: Topic 12

Black Body Radiation

The ideal body that has the ability to emit and absorb all frequencies is a black body. And the corresponding radiation emitted by a black body is black body radiation.

NCERT Notes for Class 11 Chemistry Chapter 2: Topic 13

Planck's Quantum Theory

  • Max Planck put forward a theory for explaining the phenomenon of blackbody radiation and the photoelectric effect. The theory focuses on

  • The radiant energy absorbed or omitted is in the form of small pockets of energy and these small pockets of energy are quantum.

  • The energy of each Quantum is directly proportional to the frequency of the radiation emitted.

E= hv

NCERT Notes for Class 11 Chemistry Chapter 2: Topic 14

Photoelectric Effect

When a beam of light passes on the surface of some metals electrons are emitted from the metal surface. This phenomenon is the photoelectric effect. And it has been observed that only photons of light of a particular frequency that is the threshold frequency can cause the photoelectric effect. The kinetic energy of the electron emitted from the surface of the metal is directly proportional to the frequency of the striking photons. And also when the intensity of the photon of the light is increasing more electrons are ejected.


Photoelectric effect

NCERT Notes for Class 11 Chemistry Chapter 2: Topic 15

Dual Behavior of Electromagnetic Radiation

Light and other electromagnetic radiation consist of a dual nature. That is they have particle and wave-like properties. Radiations emitted with the matter show the properties of a particle lies by exhibiting propagation. Electrons also exhibit wave-particle duality.

NCERT Notes for Class 11 Chemistry Chapter 2: Topic 16


When a light ray passes through a prism the wave which is having a short wavelength forms a colored band more than the one which is having a longer wavelength. These bands then spread to form a series of colored bands and are called the spectrum. The one which is deviated least is the one which is having the longest wavelength that is their red color.

Continuous spectrum

When white light is passed through a prism it will split seven different colored bands just like a rainbow and these colors are continuous and it is called the continuous spectrum.

Emission spectra

When radiation is emitted from a source and is then passed to a prism which is then received on a photographic plate it is called the emission spectra. The emission spectrum can be observed by heating a substance with a high temperature.

Line spectra

The vapors of some volatile substance when allowed to fall on the flame of a bunsen burner and which is further analyzed with the help of spectroscopy some specific colored lines appear on the photographic plate. And the colored lines differ for a different substance. Sodium emit yellow light while potassium emit violet light

Absorption spectra

A ray of light, when allowed to pass through the vapors of a substance and the transmitted light, is then allowed to strike a prism dark lines appear. The dark line represents that the radiations corresponding to them are absorbed by the substance. And the spectrum is called the absorption spectrum.

NCERT Notes for Class 11 Chemistry Chapter 2: Topic 17

Line Spectrum of Hydrogen

In the discharge October under low pressure when an electric discharge is passed through the hydrogen gas light is emitted and is analyzed by spectroscopy The spectrum consisting of a large number of lines is obtained and the spectrum is called the hydrogen spectrum. The series of lines is named as Lyman series, Balmer series, Paschen series, Brackett series, and Pfund series.

NCERT Notes for Class 11 Chemistry Chapter 2: Topic 18

Bohr's Model of An Atom

Bohr's model of the atom is based on Planck's Quantum theory. According to this model in an atom, the electron revolves around the nucleus in a definite circular path called the orbits. Each orbit has definite energy and it can be named as the energy levels. The energy orbits that are permitted for an electron are in which the angular momentum of the electron is an old multiple of h/2π. And when an electron is present in an orbit it neither losses nor absorbs energy it will remain in a constant form. But when energy is supplied to an electron it will jump into a higher energy state that is the excited state.

Achievements of Bohr's theory

  • It has been explained the stability of an atom.

  • It also helps for calculating the energy of an electron in a hydrogen atom and also for one-electron species.

NCERT Notes for Class 11 Chemistry Chapter 2: Topic 19

Quantum Mechanical Model of The Atom

  • Theoretical science that deals with the study of the motion of microscopic objects that have both particle-like and wave-like properties.

  • The energy of an electron in an atom is in a quantized state.

  • Due to the wavelike properties of electrons, it will exist in the quantized electronic energy level.

  • The exact position and exact velocity of an electron in an atom cannot be found out simultaneously.

  • For an atomic orbital, it has a wave function

  • The square of the orbital wave function 2 is the probability of finding an electron.

Quantum numbers

As the atomic energy levels or the orbits are quantized that can be expressed in the terms of quantum number. Quantum numbers are;

  • Principal

  • Azimuthal

  • Magnetic

  • Spin

Significance of NCERT Notes for Class 11 Chemistry Chapter 2

Notes for Class 11 Chemistry chapter 2 focuses on the main points regarding the structure of atoms. Structure of Atom Class 11 notes pdf download will help students by providing quick revision before going for the examination. CBSE Class 11 Chemistry chapter 2 notes will also give key points for students who wish to crack NEET and JEE MAIN exams. These notes will also help students in getting high marks in many competitive examinations. Structure of atoms Class 10 notes will make students study in the offline mode. cbse class 11 chemistry ch 2 notes is good source to boost the overall preparation.

NCERT Class 11 Notes Chapter-Wise

Subject Wise NCERT Exemplar Solutions

Subject Wise NCERT Solutions

Frequently Asked Question (FAQs)

1. 1. What are the limitations of the atom model proposed by Bohr?

A detailed explanation of the Bohr atom model is provided in the ch 2 chemistry class 11 notes.

  • It is cannot able to explain the atomic spectra of species containing more than one electron. 

  • The fine structure of spectral lines does not explain the well. 

  • The does not give any satisfactory explanation for the stark effect and Zeeman effect. 

  • Do not follow the Heisenberg uncertainty principle.

2. 2. Explain the Rutherford model of the atom?

According to Rutherford’s model of an atom, the positive charge is a very small region in an atom. And the small portion is named a nucleus. Surrounding the nucleus electrons are present and they move in a circular path called the orbit. The electrostatic force of attraction is holding the electrons and nucleus. A detailed view is provided in the chemistry class 11 chapter 2 notes pdf .

3. 3. Whether the topic atomic structure is tough?

This topic is very important and compared to other topics it is easy to score good marks. The basic information regarding an atom that is proton, neutron, electron, and nucleus is very important for future studies too. further you can read the topics in ch 2 chemistry class 11 notes provided here. 

4. 4. Who introduced atomic structure?

John Dalton

5. 5. What is JJ Thomson's model of the atom?

A sphere of positively charged particles and electrons is embedded in it is an atom. In the Class 11, the Structure of Atom notes this topic is clearly explained.


Get answers from students and experts

A block of mass 0.50 kg is moving with a speed of 2.00 ms-1 on a smooth surface. It strikes another mass of 1.00 kg and then they move together as a single body. The energy loss during the collision is

Option 1)

0.34\; J

Option 2)

0.16\; J

Option 3)

1.00\; J

Option 4)

0.67\; J

A person trying to lose weight by burning fat lifts a mass of 10 kg upto a height of 1 m 1000 times.  Assume that the potential energy lost each time he lowers the mass is dissipated.  How much fat will he use up considering the work done only when the weight is lifted up ?  Fat supplies 3.8×107 J of energy per kg which is converted to mechanical energy with a 20% efficiency rate.  Take g = 9.8 ms−2 :

Option 1)

2.45×10−3 kg

Option 2)

 6.45×10−3 kg

Option 3)

 9.89×10−3 kg

Option 4)

12.89×10−3 kg


An athlete in the olympic games covers a distance of 100 m in 10 s. His kinetic energy can be estimated to be in the range

Option 1)

2,000 \; J - 5,000\; J

Option 2)

200 \, \, J - 500 \, \, J

Option 3)

2\times 10^{5}J-3\times 10^{5}J

Option 4)

20,000 \, \, J - 50,000 \, \, J

A particle is projected at 600   to the horizontal with a kinetic energy K. The kinetic energy at the highest point

Option 1)


Option 2)

\; K\;

Option 3)


Option 4)


In the reaction,

2Al_{(s)}+6HCL_{(aq)}\rightarrow 2Al^{3+}\, _{(aq)}+6Cl^{-}\, _{(aq)}+3H_{2(g)}

Option 1)

11.2\, L\, H_{2(g)}  at STP  is produced for every mole HCL_{(aq)}  consumed

Option 2)

6L\, HCl_{(aq)}  is consumed for ever 3L\, H_{2(g)}      produced

Option 3)

33.6 L\, H_{2(g)} is produced regardless of temperature and pressure for every mole Al that reacts

Option 4)

67.2\, L\, H_{2(g)} at STP is produced for every mole Al that reacts .

How many moles of magnesium phosphate, Mg_{3}(PO_{4})_{2} will contain 0.25 mole of oxygen atoms?

Option 1)


Option 2)

3.125 × 10-2

Option 3)

1.25 × 10-2

Option 4)

2.5 × 10-2

If we consider that 1/6, in place of 1/12, mass of carbon atom is taken to be the relative atomic mass unit, the mass of one mole of a substance will

Option 1)

decrease twice

Option 2)

increase two fold

Option 3)

remain unchanged

Option 4)

be a function of the molecular mass of the substance.

With increase of temperature, which of these changes?

Option 1)


Option 2)

Weight fraction of solute

Option 3)

Fraction of solute present in water

Option 4)

Mole fraction.

Number of atoms in 558.5 gram Fe (at. wt.of Fe = 55.85 g mol-1) is

Option 1)

twice that in 60 g carbon

Option 2)

6.023 × 1022

Option 3)

half that in 8 g He

Option 4)

558.5 × 6.023 × 1023

A pulley of radius 2 m is rotated about its axis by a force F = (20t - 5t2) newton (where t is measured in seconds) applied tangentially. If the moment of inertia of the pulley about its axis of rotation is 10 kg m2 , the number of rotations made by the pulley before its direction of motion if reversed, is

Option 1)

less than 3

Option 2)

more than 3 but less than 6

Option 3)

more than 6 but less than 9

Option 4)

more than 9

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