Ch 1-Atomic Structure
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Transcript of Ch 1-Atomic Structure
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8/13/2019 Ch 1-Atomic Structure
1/20
Atomic Structure
Dr. R. D. Senthilkumar,
Assistant Head, Dept. of Math & Appl. Science
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8/13/2019 Ch 1-Atomic Structure
2/20
Dr. R.D. Senthilkumar, Asst. Head, Dept. of Math & Appl. Sciences, MEC
Intended Learning Outcomes
After the completion of this class, you will be
able to:
Describe the atom and its sub particles
Recall the properties of atom and its sub-particles
Explain the structure of atom (Bohr atomic model)
Calculate Bohr radius of orbit
Determine the velocity and frequency of revolving
electron
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8/13/2019 Ch 1-Atomic Structure
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Dr. R.D. Senthilkumar, Asst. Head, Dept. of Math & Appl. Sciences, MEC
What is fundamental ?
A eternal question
People have long asked that what is the world made up of?
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Dr. R.D. Senthilkumar, Asst. Head, Dept. of Math & Appl. Sciences, MEC
Answer is
Atom
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Dr. R.D. Senthilkumar, Asst. Head, Dept. of Math & Appl. Sciences, MEC
What is an atom?
A fundamental particle of matter
Very smaller in size
Consists of electron, nucleus (proton andneutron)
Has both negative and positive charges
Atoms are stable Atoms can stick together to form molecules
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8/13/2019 Ch 1-Atomic Structure
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Dr. R.D. Senthilkumar, Asst. Head, Dept. of Math & Appl. Sciences, MEC
Structure of an atom
Electron
Proton Neutron
Electron Proton Neutron
Discovered by JJ Thomson Rutherford James Chadwick
Charge -1.6 x 10-19 C +1.6 x 10-19C No Charge
Mass 9.1110-31Kg 1.673 10-27 Kg 1.675 10-27 Kg
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8/13/2019 Ch 1-Atomic Structure
7/20Dr. R.D. Senthilkumar, Asst. Head, Dept. of Math & Appl. Sciences, MEC
Atomic models
To explain the structure of atom, several
theories have been proposed called as atomic
models and they are
Thomsons model
Rutherfords nuclear model
Bohrs atom model Sommerfelds relativistic model
Vector atom model
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8/13/2019 Ch 1-Atomic Structure
8/20Dr. R.D. Senthilkumar, Asst. Head, Dept. of Math & Appl. Sciences, MEC
Thomson atom model
According to this model, Atom is a heavy sphere about 10-10m in
diameter
Electrons and positive particles are uniformlydistributed inside the spherical atom
Repulsive force between two adjacentelectrons is balanced by the equal andopposite attractive forces acting betweenelectron and positive particle
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8/13/2019 Ch 1-Atomic Structure
9/20Dr. R.D. Senthilkumar, Asst. Head, Dept. of Math & Appl. Sciences, MEC
Thomson atom model contd
Electron
Positive
particles
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8/13/2019 Ch 1-Atomic Structure
10/20Dr. R.D. Senthilkumar, Asst. Head, Dept. of Math & Appl. Sciences, MEC
Rutherfords nuclear atomic model
Rutherford, in 1911, proposed a new type ofmodel of the atom
According to this model,
Positive charge of the atom is concentrated in avery small volume (< 10-13cm in dia) at its centre.This central core is called nucleus
Nucleus is surrounded by Electrons are revolving
around the nucleus in a spiral orbits. Hence, the entire atom becomes electrically
neutral
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11/20Dr. R.D. Senthilkumar, Asst. Head, Dept. of Math & Appl. Sciences, MEC
Rutherfords model
Spiral orbit
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12/20Dr. R.D. Senthilkumar, Asst. Head, Dept. of Math & Appl. Sciences, MEC
Drawbacks of Rutherfords nuclear
atomic model
The stability of the atom as a whole
Distribution of electrons around the nucleus
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8/13/2019 Ch 1-Atomic Structure
14/20Dr. R.D. Senthilkumar, Asst. Head, Dept. of Math & Appl. Sciences, MEC
Bohrs atom model contd
Electron
Proton Neutron
Circular orbit
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8/13/2019 Ch 1-Atomic Structure
15/20Dr. R.D. Senthilkumar, Asst. Head, Dept. of Math & Appl. Sciences, MEC
Bohrs theory of hydrogen atom
Bohr explained the hydrogen atom based onthe following assumptions:
Electron in an atom moves in a circular orbitaround the nucleus under the influence ofCoulomb force of attraction between the
electron and nucleus (entire atom is stable asCoulomb force of attraction is balanced byNewtonian centrifugal force as shown in fig.)
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8/13/2019 Ch 1-Atomic Structure
16/20Dr. R.D. Senthilkumar, Asst. Head, Dept. of Math & Appl. Sciences, MEC
Bohrs theory of hydrogen atom
contd
2
0
2
4 r
e
r
mv
2
=
Coulomb force
Centrifugalforce
+Z e
- ev
r
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8/13/2019 Ch 1-Atomic Structure
17/20Dr. R.D. Senthilkumar, Asst. Head, Dept. of Math & Appl. Sciences, MEC
Bohrs theory of hydrogen atom
contd
Only particular orbits are allowed in an atom
Electron moving in such allowed orbit does notemit or absorb the radiation (total energy of
the electron revolving in any one of the so manyallowed orbits remains constant)
Radiation is emitted when an electron jumpsfrom higher energy(E2) orbit to lower energy (E1)
orbit. Frequency (h) of emitted radiation isrelated by the equation
E2E1= h
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8/13/2019 Ch 1-Atomic Structure
19/20Dr. R.D. Senthilkumar, Asst. Head, Dept. of Math & Appl. Sciences, MEC
Formulae
Bohrs radius of orbit rn= n2x ao
where, n - no. of orbit & ao= 0.529x10-10metre
Velocity of revolving electron v = nh/2mr
Where, h is Plancks constant = 6.626x10-34Joule-sec
m is mass of electron = 9.11x10-31kg
r is radius of nthorbit
Frequency of revolving electron f = v/2r
Where v is the velocity of electron.
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8/13/2019 Ch 1-Atomic Structure
20/20D R D S thilk A t H d D t f M th & A l S i MEC