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UNIT 2: STRUCTURE OF ATOM

Atom was earlier considered the most fundamental and indivisible unit of matter. Daltons

Atomic Theory considered atom as the most fundamental unit of matter and thus believed it

to be indivisible. But further on Sub atomic particles were discovered like electron, protons,

neutrons, etc.

Electrons were discovered in the Cathode Ray tube experiment. Adding to this J.J

Thompson found out the charge to mass ratio of an electron. R.A Millikan found out the

value of charge on an electron with his oil drop experiment, and using the ratio of J.J

Thompson was able to find out the mass too. A simple modification of the cathode ray tubes

lead to the discovery of canal rays, particles carrying positive charge, thus, protons were

discovered. Eventually, due to the aspect of stabilizing the atom neutrons were discovered by

Chadwick. Neutrons have a mass slightly higher than the protons and have no charge.

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Now, since so many particles came up, thus there was a need to

visualize how these particles were arranged in an atom, thus

experimentalists started making atomic models, many came up with

distinct ideas but had to face serious limitations and drawbacks. Lord

Rutherford came up with an idea of the model like the solar system,

and his model was also called the solar system model. To put

limitations to his model James Clark Maxwell had already developed a

theory known as the electromagnetic theory of Maxwell.

Thus such models, though not perfect still helped the early

scientists to work on their own model in a more comprehensive way,

and also lead to the development of the Bohr model of atom, the twodevelopments which played an important role in the formulation of

Bohrs model were:

1. Dual character of electromagnetic radiation, which means radiation

has both wave and particle nature.

2. Experiments on atomic spectra, and the quantization of energy

levels.

Sir James Clark Maxwell gave the theory on wave nature of

electromagnetic radiation; by this he was able to explain the

phenomenon of charged particles on macroscopic level. He explained

that if a charge particle is accelerated then it emits electromagnetic

radiation, which is in fact a form of energy. Maxwell also proved that

light itself is an electromagnetic wave. Many phenomenon likediffraction, interference etc. could be explained by Maxwells theory,

but certain phenomenon seem to deviate from Maxwells

electromagnetic theory. Some of those phenomenon are:

1. Nature of emission of radiation: Black Body radiation.

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2. Ejection of electrons when radiation strikes the metal: The

Photoelectric effect.

3. Variation of heat capacity of solids as a function of temperature.

4. Line Spectra of atoms, with special reference to hydrogen.

Thus, to overcome this problem a theory was put forward by Max

Plank, the main and basic idea of his theory was that atoms and

molecules could emit or absorb energy(light) only in discrete

amounts and not in a continuous manner, thus to the smallest

quantity of energy Plank gave the name Quantum.

UNIT 2: STRUCTURE OF ATOM

Atom was earlier considered the most fundamental and indivisible

unit of matter. Daltons Atomic Theory considered atom as the most

fundamental unit of matter and thus believed it to be indivisible. But

further on Sub atomic particles were discovered like electron,

protons, neutrons, etc.

8/12/2019 dsfgdsf

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Electrons were discovered in the Cathode Ray tube experiment.

Adding to this J.J Thompson found out the charge to mass ratio of an

electron. R.A Millikan found out the value of charge on an electron

with his oil drop experiment, and using the ratio of J.J Thompson was

able to find out the mass too. A simple modification of the cathode ray

tubes lead to the discovery of canal rays, particles carrying positive

charge, thus, protons were discovered. Eventually, due to the aspect of

stabilizing the atom neutrons were discovered by Chadwick. Neutrons

have a mass slightly higher than the protons and have no charge.

Now, since so many particles came up, thus there was a need to

visualize how these particles were arranged in an atom, thusexperimentalists started making atomic models, many came up with

distinct ideas but had to face serious limitations and drawbacks. Lord

Rutherford came up with an idea of the model like the solar system,

and his model was also called the solar system model. To put

limitations to his model James Clark Maxwell had already developed a

theory known as the electromagnetic theory of Maxwell.

Thus such models, though not perfect still helped the early

scientists to work on their own model in a more comprehensive way,

and also lead to the development of the Bohr model of atom, the two

developments which played an important role in the formulation of

Bohrs model were:

1. Dual character of electromagnetic radiation, which means radiation

has both wave and particle nature.

2. Experiments on atomic spectra, and the quantization of energy

levels.

8/12/2019 dsfgdsf

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Sir James Clark Maxwell gave the theory on wave nature of

electromagnetic radiation; by this he was able to explain the

phenomenon of charged particles on macroscopic level. He explained

that if a charge particle is accelerated then it emits electromagnetic

radiation, which is in fact a form of energy. Maxwell also proved that

light itself is an electromagnetic wave. Many phenomenon like

diffraction, interference etc. could be explained by Maxwells theory,

but certain phenomenon seem to deexperimentalists started making

atomic models, many came up with distinct ideas but had to face

serious limitations and drawbacks. Lord Rutherford came up with an

idea of the model like the solar system, and his model was also called

the solar system model. To put limitations to his model James Clark

Maxwell had already developed a theory known as the

electromagnetic theory of Maxwell.

Thus such models, though not perfect still helped the early

scientists to work on their own model in a more comprehensive way,

and also lead to the development of the Bohr model of atom, the two

developments which played an important role in the formulation of

Bohrs model were:

1. Dual character of electromagnetic radiation, which means radiation

has both wave and particle nature.

2. Experiments on atomic spectra, and the quantization of energy

levels.

Sir James Clark Maxwell gave the theory on wave nature of

electromagnetic radiation; by this he was able to explain the

phenomenon of charged particles on macroscopic level. He explained

that if a charge particle is accelerated then it emits electromagnetic

radiation, which is in fact a form of energy. Maxwell also proved that

light itself is an electromagnetic wave. Many phenomenon like

diffraction, interference etc. could be explained by Maxwells theory,

but certain phenomenon seem to deviate from Maxwellselectromagnetic theory. Some of those phenomenon are:

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1. Nature of emission of radiation: Black Body radiation.

2. Ejection of electrons when radiation strikes the metal: The

Photoelectric effect.

3. Variation of heat capacity of solids as a function of temperature.

4. Line Spectra of atoms, with special reference to hydrogen.

Thus, to overcome this problem a theory was put forward by Max

Plank, the main and basic idea of his theory was that atoms and

molecules could emit or absorb energy(light) only in discrete

amounts and not in a continuous manner, thus to the smallest

quantity of energy Plank gave the name Quantum.

UNIT 2: STRUCTURE OF ATOM

Atom was earlier considered the most fundamental and indivisible

unit of matter. Daltons Atomic Theory considered atom as the most

fundamental unit of matter and thus believed it to be indivisible. But

further on Sub atomic particles were discovered like electron,

protons, neutrons, etc.

8/12/2019 dsfgdsf

7/12

Electrons were discovered in the Cathode Ray tube experiment.

Adding to this J.J Thompson found out the charge to mass ratio of an

electron. R.A Millikan found out the value of charge on an electron

with his oil drop experiment, and using the ratio of J.J Thompson was

able to find out the mass too. A simple modification of the cathode ray

tubes lead to the discovery of canal rays, particles carrying positive

charge, thus, protons were discovered. Eventually, due to the aspect of

stabilizing the atom neutrons were discovered by Chadwick. Neutrons

have a mass slightly higher than the protons and have no charge.

Now, since so many particles came up, thus there was a need to

visualize how these particles were arranged in an atom, thusexperimentalists started making atomic models, many came up with

distinct ideas but had to face serious limitations and drawbacks. Lord

Rutherford came up with an idea of the model like the solar system,

and his model was also called the solar system model. To put

limitations to his model James Clark Maxwell had already developed a

theory known as the electromagnetic theory of Maxwell.

Thus such models, though not perfect still helped the early

scientists to work on their own model in a more comprehensive way,

and also lead to the development of the Bohr model of atom, the two

developments which played an important role in the formulation of

Bohrs model were:

1. Dual character of electromagnetic radiation, which means radiation

has both wave and particle nature.

2. Experiments on atomic spectra, and the quantization of energy

levels.

8/12/2019 dsfgdsf

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Sir James Clark Maxwell gave the theory on wave nature of

electromagnetic radiation; by this he was able to explain the

phenomenon of charged particles on macroscopic level. He explained

that if a charge particle is accelerated then it emits electromagnetic

radiation, which is in fact a form of energy. Maxwell also proved that

light itself is an electromagnetic wave. Many phenomenon like

diffraction, interference etc. could be explained by Maxwells theory,

but certain phenomenon seem to deexperimentalists started making

atomic models, many came up with distinct ideas but had to face

serious limitations and drawbacks. Lord Rutherford came up with an

idea of the model like the solar system, and his model was also called

the solar system model. To put limitations to his model James Clark

Maxwell had already developed a theory known as the

electromagnetic theory of Maxwell.

Thus such models, though not perfect still helped the early

scientists to work on their own model in a more comprehensive way,

and also lead to the development of the Bohr model of atom, the two

developments which played an important role in the formulation of

Bohrs model were:

1. Dual character of electromagnetic radiation, which means radiation

has both wave and particle nature.

2. Experiments on atomic spectra, and the quantization of energy

levels.

Sir James Clark Maxwell gave the theory on wave nature of

electromagnetic radiation; by this he was able to explain the

phenomenon of charged particles on macroscopic level. He explained

that if a charge particle is accelerated then it emits electromagnetic

radiation, which is in fact a form of energy. Maxwell also proved that

light itself is an electromagnetic wave. Many phenomenon like

diffraction, interference etc. could be explained by Maxwells theory,

but certain phenomenon seem to deviate from Maxwellselectromagnetic theory. Some of those phenomenon are:

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1. Nature of emission of radiation: Black Body radiation.

2. Ejection of electrons when radiation strikes the metal: The

Photoelectric effect.

3. Variation of heat capacity of solids as a function of temperature.

4. Line Spectra of atoms, with special reference to hydrogen.

Thus, to overcome this problem a theory was put forward by Max

Plank, the main and basic idea of his theory was that atoms and

molecules could emit or absorb energy(light) only in discrete

amounts and not in a continuous manner, thus to the smallest

quantity of energy Plank gave the name Quantum.

UNIT 2: STRUCTURE OF ATOM

Atom was earlier considered the most fundamental and indivisible

unit of matter. Daltons Atomic Theory considered atom as the most

fundamental unit of matter and thus believed it to be indivisible. But

further on Sub atomic particles were discovered like electron,

protons, neutrons, etc.

8/12/2019 dsfgdsf

10/12

Electrons were discovered in the Cathode Ray tube experiment.

Adding to this J.J Thompson found out the charge to mass ratio of an

electron. R.A Millikan found out the value of charge on an electron

with his oil drop experiment, and using the ratio of J.J Thompson was

able to find out the mass too. A simple modification of the cathode ray

tubes lead to the discovery of canal rays, particles carrying positive

charge, thus, protons were discovered. Eventually, due to the aspect of

stabilizing the atom neutrons were discovered by Chadwick. Neutrons

have a mass slightly higher than the protons and have no charge.

Now, since so many particles came up, thus there was a need to

visualize how these particles were arranged in an atom, thusexperimentalists started making atomic models, many came up with

distinct ideas but had to face serious limitations and drawbacks. Lord

Rutherford came up with an idea of the model like the solar system,

and his model was also called the solar system model. To put

limitations to his model James Clark Maxwell had already developed a

theory known as the electromagnetic theory of Maxwell.

Thus such models, though not perfect still helped the early

scientists to work on their own model in a more comprehensive way,

and also lead to the development of the Bohr model of atom, the two

developments which played an important role in the formulation of

Bohrs model were:

1. Dual character of electromagnetic radiation, which means radiation

has both wave and particle nature.

2. Experiments on atomic spectra, and the quantization of energy

levels.

8/12/2019 dsfgdsf

11/12

Sir James Clark Maxwell gave the theory on wave nature of

electromagnetic radiation; by this he was able to explain the

phenomenon of charged particles on macroscopic level. He explained

that if a charge particle is accelerated then it emits electromagnetic

radiation, which is in fact a form of energy. Maxwell also proved that

light itself is an electromagnetic wave. Many phenomenon like

diffraction, interference etc. could be explained by Maxwells theory,

but certain phenomenon seem to deviate from Maxwells

electromagnetic theory. Some of those phenomenon are:

1. Nature of emission of radiation:Black Body radiation.2. Ejection of electrons when radiation

strikes the metal: The Photoelectric

effect.3. Variation of heat capacity of solids asa function of temperature.4. Line Spectra of atoms, with special

reference to hydrogen.Thus, to overcome this problem a

theory was put forward by Max Plank,the main and basic idea of his theory

was that atoms and molecules could

emit or absorb energy(light) only in

discrete amounts and not in a

continuous manner, thus to the smallest

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quantity of energy Plank gave the name

Quantum.