Bohr’s model of Atom:
By utilizing the previous model’s on atom and molecules, Neils Bohr developed his own model. In Bohr’s model two major developments were introduced :
- Electromagnetic radiations having both wave-like and particle-like properties.
- The experimental results of atomic spectra.
Wave
nature of electromagnetic radiation:
In
the mid-nineteenth century, physicists studied that thermal radiations that are
emitted by heated objects consist of electromagnetic waves of various
frequencies or wavelengths. But James Maxwell in 1870 was the first who gives a
good explanation about the electromagnetic waves or radiation, where he
suggested that when any electrically charged particles are under acceleration,
they produce and transmit alternating electrical and magnetic fields which are
transmitted in the form of waves.
Maxwell
also reveals- the oscillating electric and magnetic character of light waves.
After considering all the aspects we can summaries the properties in these
points:
· When oscillating
charged particles produce oscillating electric and magnetic fields, they are
perpendicular to each other and also perpendicular to the direction of the flow
of waves.
·
Electromagnetic
waves can move in a vacuum without any medium.
·
Different
electromagnetic radiations have different types of wavelength
or frequency.
· And different
kind of unit is used to define electromagnetic waves like frequency(ν), wavelength(λ).
Particle
nature of electromagnetic radiation:
Planck’s
Quantum theory:
Max
Planck in 1900, first gave an explanation of black body radiation. As per him,
the intensity of radiations of a different wavelength that is emitted by a hot
body always depends on its own temperature. A black body is an ideal body that
absorbs and emits radiations of all frequencies and such radiations are called black
body radiation. Carbon is an element which nearly close to a black body
however, no such body exists. He also
suggested that atoms and molecules could emit or absorb energy in discrete
quantities. The smallest quantity of energy that is emitted or absorbed in an
atom in the form of electromagnetic radiation that he named Quantum. The
Energy(E) of a quantum of radiation is directly proportional to its
frequency(ν) and expressed as:
E= hν
The
proportionality constant ‘h’ is known as Planck’s constant, where h=
6.626×10-34 Js.
By introducing this theory Planck was able to explain the changes in frequency and wavelengths of black body radiation with the changes in temperature. Keep in touch with us for more interesting topics and subscribe @A-Z pharmascience for instant updates.
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