STRUCTURE OF ATOM
NAME:- PINAKI BANDYOPADHYAY
• various model of atom
J.J. Thomson model of atom
Rutherford alpha-scattering experiment
• Electromagnetic wave theory
• Planck’s Quantum theory
• Photoelectric effect
• Dual behavior of matter
• Heisenberg’s uncertainty principle
Various Models of Atom
J.J. Thomson Model of Atom
This model of atom is given by J.J. Thomson in 1904. In this model,
There Is a positive sphere in which positive charge is uniformly
distributed like pulp in melon and electrons is embedded in this
positive sphere like seed in melon.
Rutherford alpha- scattering
Rutherford and his student bombarded very thin gold foil alpha-
particle. A stream of alpha-particle from radioactive source was
directed towards thin gold foil( thickness~ 100nm) of gold metal.
The thin gold foil had a circular fluorescent zinc sulphide screen
around it. Whenever alpha-particle struck the screen , a tiny flash of
light was produced at that point.
most of the alpha-particle passed
through the gold foil undeflected.
a small fraction of the alpha-particle
a deflected by small angles.
a very few alpha-particle(~ 1 in
20,000) bounded back, that is, were
deflected by 180 degree.
There is most of the space empty in atom.
The positive charge has to be concentrated in a
very small region that repelled and deflected the
positively charged alpha-particle.
size of nucleus is very smaller than size of atom
i.e., nucleus= 10 to the power -15 & atom= 10 to
the power -10.
Why Gold foil Is used?
• Gold is highly malleable; gold leaf can be made
in thicknesses around 100 nm or 4 micro-inch.
• Most of the element after gold is radioactive. It
is used because gold was known to be a very
• To increase the probability of an alpha particle
hitting a nucleus, the more you have in a given
volume, the better you chances. Gold has a
density of 19.3 grams per cubic centimeter.
Nucleus & Orbits
Nucleus:- The positive charge and most of the mass of
the atom was densely concentrated in extremely small
region. This part is called nucleus. It contain neutron &
Orbits:- The electron move in circular path around
nucleus called orbit.
Limitation of Rutherford model
• The Rutherford model cannot explain the
stability of an atom.
• According to EMW(Electro Magnetic Wave)
theory, if a charged particle accelerate then it
radiate energy and the path of orbit shrink and
electron will spiral into nucleus.
• It say nothing about the electronic structure of
Electromagnetic wave theory
James Clerk Maxwell (1831-1879) – Scottish
mathematician and physicist developed this.
• Unified existing laws of electricity and magnetism
• Oscillating electric field produces a magnetic field
(and vice versa) – propagates an EM wave
According to EMW, Electron Spiral into Nucleus
Absorption spectrum & Emission spectrum
• The electromagnetic spectrum, broken by a specific
pattern of dark lines or bands, observed when radiation
traverses a particular absorbing medium. The absorption
pattern is unique and can be used to identify the
material. This is called absorption spectrum.
• The spectrum of bright lines, bands, or continuous
radiation characteristic of and determined by a specific
emitting substance subjected to a specific kind of
excitation. spectrum of electromagnetic radiation emitted
by a self-luminous source. This is called emission
Planck’s Quantum theory
Max Planck showed that the energy of light is proportional
to its frequency, also showing that light exists in
Discrete quanta of energy.
Wavelength of a wave:-
The distance used to determine the wavelength of
a wave is shown. Light has many properties
associated with its wave nature, and the
wavelength in part determines these properties.
Frequency of Wave
It Is defined as number of waves that pass a given
point in one second.
Wave number:- It is defined as the number of
Wavelengths per unit length.
Planck’s constant:- i.e., h=6.626X10 to the power
The photons of a light beam have a characteristic
energy proportional to the frequency of the light.
In the photoemission process, if an electron within
some material absorbs the energy of one photon and acquires more
energy than the work function (the electron binding energy) of the
material, it is ejected. If the photon energy is too low, the electron is
unable to escape the material. Increasing the intensity of the light beam
increases the number of photons in the light beam, and thus increases
the number of electrons excited, but does not increase the energy that
each electron possesses. The energy of the emitted electrons does not
depend on the intensity of the incoming light, but only on the energy or
frequency of the individual photons. It is an interaction between the
incident photon and the outermost electrons.
Electrons can absorb energy from photons when irradiated,
but they usually follow an "all or nothing" principle. All of the
energy from one photon must be absorbed and used to
liberate one electron from atomic binding, or else the
energy is re-emitted. If the photon energy is absorbed,
some of the energy liberates the electron from the atom,
and the rest contributes to the electron's kinetic energy as a
• "electric eye", light meter, movie film audio track.
• photoconductivity: an increase in the electrical conductivity of a
nonmetallic solid when exposed the electromagnetic radiation. The
increase in conductivity is due to the addition of free electrons
liberated by collision with photons. The rate at which free electrons
are generated and the time they over which the remain free
determines the amount of the increase.
• photovoltaic's: the ejected electron travels through the emitting
material to enter a solid electrode in contact with the photo emitter
(instead of traveling through a vacuum to an anode) leading to the
direct conversion of radiant energy to electrical energy.
• photo static copying .
Dual behavior of Matter
Wave–particle duality postulates that all particles exhibit
both wave and particle properties.
The photon has momentum as well as
Wavelength, De Broglie, from the analogy,
Gave the following relation:-
h= Planck’ constant,
Einstein is most famous for saying "mass is related
to energy". Of course, this is usually written out as
an equation, rather than as words:
E=m X c X c ---------------------(1)
wave's frequency by the equation:
E=h X v(nu) ---------------------(2)
Combining the 1st & 2nd eq.,
Lambda=h/mv (since, c=v)
Heisenberg’s Uncertainty Principle
It states that it is impossible to determine Simultaneously,
the exact position and exact momentum(or velocity) of an
x(delta) X p(delta)=h/4X3.14(pie).