1. Ernst Rutherford
Rutherford was born at Nelson , New
Zealand. He was educated at University
of New Zealand and conducted research
work in 1895 with J . J . Thomson at the
Cavendish Laboratory . In 1907 , he
accepted Longworthy Professorship at
Manchester University in England where
Chawdick was one of his students. He
won Noble Prize in 1908 in the field of
2. He explained that the major portion of
the atomic mass is concentrated in a
minute , centrally located , positively
charged nucleus. As early as in 1920 ,
he predicted the presence of particles
with unit mass but having no charge . He
named such particles neutrons.
Rutherford scattering is a phenomenon
in physics that was explained by Ernest
Rutherford in 1911, which led to the
development of the Rutherford
model (planetary model) of the atom,
and eventually to the Bohr model. It is
now exploited by the
technique Rutherford backscattering.
4. Rutherford concluded from the alpha
particles scattering experiment that –
a) Most of the space inside the atom is
empty because most of the alpha
particles passed through the gold foil
without getting deflected.
b) Very few particles were deflected
from their path, indicating that the
positive charge of the atom occupies
very little space.
5. c) A very small fraction of alpha particles
were deflected by 180 indicating that
all the positive charges and mass of the
gold atom were concentrated in a very
small volume within the atom
6. RutheRfoRd’s nucleaR
Model of an Atom
The main points of Rutherford’s
nuclear model are described below :
a) An atom consists of a positively
charged nucleus, which is surrounded
by electrons moving around it.
b) Electrons and the nucleus are held
together by coulombic force of
7. c) The size of nucleus is very small as compared
to the size of atom . Experimentally, it was
found that ,
Radius of the nucleus of an atom=10 to 10 m
Radius of an atom =10-10m
Thus, the size of the nucleus is about tenthousandth part of the size of an atom.
d) Almost the entire mass of an atom is
concentrated in its nucleus.
e) Atom , as a whole , is electrically neutral. So ,
number of protons inside the nucleus of an
atom and the number of electrons
surrounding the nucleus are equal .
8. how RutheRfoRd’s atomic
model Is different from
Thomson atomic model ????
Rutherford proposed a model in which
electrons revolve around the nucleus in well –
defined orbits . There is a positively charged
centre in an atom called the Nucleus . He also
proposed that the size of the nucleus is very
small as compared to the size of the atom
and nearly all the mass of an atom is centred
in the nucleus.
9. Thomson proposed the
model of an atom to be
similar to a christmas
pudding. The electros
are in a positively
charged sphere like
christmas pudding and
the mass of the atom
was supposed to be
uniformly disturbed .
10. Drawbacks of
The Rutherford’s atomic model explains the
structure of an atom in a very simple way. But
,it suffers from the following drawbacks :
a) An electron revolving around the nucleus gets
accelerated towards the nucleus. An
accelerating charged particle must emit
radiation , and lose energy .Thus , the
electrons in an atom must continuously emit
radiation and lose energy .
11. Because of this lose energy , the electron
would slow down , and will not be able to
withstand and the attraction of the nucleus .
As a result , the electron should follow a spiral
path , and ultimately fall into the nucleus. If
it happens , then the atom should collapse in
about 10 second . But, this does not happen
– atoms are stable . This indicates that there
is something wrong in Rutherford’s nuclear
model of atom.
b) Rutherford’s model of atom does not say
anything about the arrangement of electron
in an atom.