RUTHERFORD’S ATOMIC THEORY
 
 
 
RUTHERFORD’S EXPERIMENT
 
APPARATUS :
  • Alpha particles.
  • Gold foil. (0.0004 cm thick)
  • Zinc sulphide screen.
  • Electron Gun.
EXPERMENT
 
In his experiment, Rutherford bombarded alpha particles on very thin gold foils and record their observations.
OBSERVATIONS
 
1. He observed that most of the alpha particles were pass through the foil undeflected.
2. Very few particles were deflected when passed through the foil.
3. One particle out of 8000 particles was rebound.
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MAIN POINTS OF RUTHERFORD’S THEORY
 
  • 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).

  • The electrons revolve around the nucleus in different circular orbits.

  • Size of nucleus is very small as compare to the size of atom.
DEFECT OF
RUTHERFORD’S THEORY
 
  • According to electromagnetic theory, being a charge particle, a revolving electron must emit energy. Due to emission of energy, the orbit of electron will decrease. 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
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ELECTRONEGATIVITY
 
"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

ATOMIC RADIUS
 
Half of the distance between the nuclei of two adjacent similar atoms is called "Atomic Radius".
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  • Atomic radius = AB / 2

  • Unit of atomic radius is Angstrom (A)

  • 1 A. = 10-10 m
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