Rutherford’s Atomic Model

  Rutherford’s atomic model shows the existence of nucleus in the atom, nature of charge on the nucleus   and the magnitude of charge on the nucleus.
  • Alpha particles.
  • Gold foil. (0.0004 cm thick)
  • Zinc sulphide screen.
  • Electron Gun.
  In his experiments, Rutherford bombarded alpha particles on very thin metallic foils such as gold foil.In     order to record experimental observations, he made use of circular screen coated with zinc sulphide.
   He observed that most of the alpha particles were pass through the foil undeflected.
Very few particles were deflected when passed through the foil.
One particle out of 8000 particles was deflected at 90o.
   Few particles were deflected at different angles.
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   Major portion of the atom is empty.

   The whole mass of the atom is concentrated in the center of atom called nucleus.

   The positively charged particles are present in the nucleus of atom.

   The charge on the nucleus of an atom is equal to (+z.e) where Z= charge number, e = charge of        proton.

   The electrons revolve around the nucleus in different circular orbits.

   Size of nucleus is very small as compare to the size of atom.

  1. Since most of the alpha particles were passed through the foil undeflected, therefore, it was concluded      that most of the atom is empty.
2. Small angles of deflection indicate that positively charged alpha particles were attracted by electrons.
3. Large angles of deflection indicate that there is a massive positively charged body present in the atom      and due to repulsion alpha particles were deflected at large angles.
  There were two fundamental defects in Rutherford’s atomic model:
According to classical electromagnetic theory, being a charge particle electron when accelerated must   emit energy. We know that the motion of electron around the nucleus is an accelerated motion, therefore,   it must radiate energy. But in actual practice this does not happen. Suppose if it happens then due to   continuous loss of energy orbit of electron must decrease continuously. Consequently electron will fall into   the nucleus. But this is against the actual situation and this shows that atom is unstable.

   If the electrons emit energy continuously, they should form continuous spectrum .But actually line     spectrum is obtained

“Relative tendency or relative power of an atom to attract shared
pair of electrons towards itself is called ELECTRONEGATIVITY

  E.N depends upon the size of atom .

  Small atoms have large values of E.N.

  Big atoms have small values of E.N.

  E.N decreases in a group.

  E.N increases in a period.

  Most Electronegatively element is “Flourine”. E.N = 4

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