CBSE Class 12-science Answered
write down the postulates of Bohr's theory. explain hydrogen spectrum on the basis of this theory
Asked by premansh128 | 21 Jan, 2021, 12:19: PM
Expert Answer
Bohr combined classical and early quantum concepts and gave his theory in the form of three postulates.
These are :
(i) Bohr’s first postulate was that an electron in an atom could revolve in certain stable orbits without
the emission of radiant energy,contrary to the predictions of electromagnetic theory.
According to this postulate, each atom has certain definite stable states in which it can exist, and each
possible state has definite total energy. These are called the stationary states of the atom.
(ii) Bohr’s second postulate defines these stable orbits. This postulate states that the electron revolves around the
nucleus only in those orbits for which the angular momentum is some integral multiple of h/2π
where h is the Planck’s constant (= 6.6 × 10–34 J s).
Thus the angular momentum (L) of the orbiting electron is quantised, i.e., L = n ( h/2π)
(ii) Third postulate states that an electron might make a transition from one of its specified non-radiating orbits
to another of lower energy. When it does so, a photon is emitted having energy equal to the energy difference
between the initial and final states.
The frequency of the emitted photon is then given by
hν = Ei – Ef
where Ei and Ef are the energies of the initial and final states and Ei > Ef .
Bohr’s third postulate is based on the early quantum concepts that had been developed by Planck and Einstein.
Answered by Thiyagarajan K | 21 Jan, 2021, 03:00: PM
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