Bohr’s Atomic Model
Bohr’s Atomic Model-In 1913, Neils Bohr, Danish Physicist gave clear explanation of atomic structure.
According to Bohr:
(i) An atom consists of a positively charged nucleus around which
negatively charged electrons revolve in different circular orbits.
(ii) The electrons can revolve around the nucleus only in certain permitted
orbits i.e. orbits of certain radii are allow.
(iii) The electrons in each permitted orbit have a certain fixed amount of
energy. The larger the orbit (i.e. larger radius), the greater is the
energy of electrons.
(iv) If an electron is give additional energy (eg heat, light etc), it is lift to
the higher orbit. The atom is say to be in a state of excitation. This
state does not last long, because the electron soon falls back to the
original lower orbit. As it falls, it gives back the acquired energy in the form of heal light or other radiations.
Bohr’s Atomic Model-Fig. 4.1 shows the structure of silicon atom. It has 14 electrons. Two
electrons revolve in the first orbit, 8 in the second orbit and 4 in the
third orbit. The first second, third orbits etc are also know as K, L, M
These electrons can revolve only in permitted orbits
(i.e orbits of *radius
r 1 , r 2 and r 3 ) and not in any arbitrary orbit. Thus, all radii between r 1 and
r 2, or between r 2 and r 3 are forbidden. Each orbit has fixed amount of
energy associated with it. If an electron in the first orbit is to be lifted to
the second orbit, just the **right amount of energy should be supplied
to it. When this electron jumps from the second orbit to first, it will give
back the acquired energy in the form of electromagnetic radiations.