Thomson model of atom
=> Give
by J.J Thomson (1898)
=> According
to J.J. Thomson atoms posses a spherical shape with radius about 10-10 m,
in which + ve charge is uniformly distributed.
=> Electrons
are embedded in such a manner to give most stable electrostatic arrangement.
=> Other
names of this model plum pudding raisin pudding watermelon.
=> Mass
is assumed to be uniformly distributed in atom.
Rutherford’s nuclear model of atom
=> Given
by Rutherford & his students Ernest Marsden and Hans Geiger.
=> By
α- particles scattering experiment-
 |
Rutherford’s nuclear model of atom |
=> When
beam of high energy α- particles was directed at gold foil then tiny flash of
light observed at photographic plate.
Rutherford observed that-
1) Most
of the α- practical passed
through gold foil undeflected :
2) A
small fraction of α- particles was deflected by small angles.
3) A
very few α- particles (about 1 in 20000) bounced back means deflected by nearly 1800
From above observations he concludes the structure of atom.
1) Most
of space in atom is empty because most of α- particles passed undeflected.
2) Few
+ve charged α- particles were deflected.
Because
+ ve charge of the atom present in center in very small volume that repelled
& deflected the +ve charged α- particles.
3) Volume
of nucleus is negligible as compared to total volume of atom
i.e. radius of atom = 10-10m (approx)
radius
of nucleus = 10-15m (approx)
On the basis of observation & conclusion Rutherford proposed model of atom as-
1) +ve
charge & most of mass present in the center of atom known as nucleus.
2) Electrons
moves around nucleus with very high speed in circular paths known as orbits.
3) Electrons
and nucleus (protons) are held together by electrostatic force of attraction .
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