Tuesday, 23 June 2015

Thomson model of atom and Rutherford’s nuclear model of atom

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 nuclear model of atom

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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