explain the rutherford's gold foil experiment with the help of diagram?


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Rutherford designed an experiment to study how alpha (α) particles, with a 2+ charge, interact with a piece of very thin gold foil. Rutherford bombarded a very thin piece of gold foil with a stream of positively charged particles known as the alpha particles.

Rutherford observed that:

  1. Most of the α-particles passed through the gold foil undeflected.
  2. Some of the α-particles were deflected by small angles.
  3. A few particles were either deflected by very large angles or were actually reflected back along their path.

Rutherford explained the observations as follows:

  1. Since most of the α-particles pass through the foil undeflected, it indicates that the most of the space in an atom is empty.
  2. Α-particle being positively charged and having considerable mass could be deflected only by some heavy, positively charged centre. The small angle of deflection of α-particles indicated the presence of a heavy positive centre in the atom. Rutherford named this positive centre as nucleus.

You can refer the images given by your friend TOXXIC.

c. Α-particles which make head-on collision with heavy positive centre are deflected through large angles. Since the number of such α-particles is very small, the space occupied by the heavy positive centre must be very small.

On the basis of experiment Rutherford put forward nuclear model of atom. Main points of this model are:

  1. There is positively charged centre in an atom called nucleus.
  2. The electrons revolve around the nucleus in well-defined path.
  3. The size of the nucleus is very small as compared to size of the atom.



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Ignore  the upper sphere


He selected a gold foil  about 1000 atoms thick. the foil was surrounded by a fluroscent zinc sulphide screen. He shot some "Alpha particles aka He2+ Ions". Whenever alpha particle strikes the screen , it produces a flash of light.. Rutherford expected that the fast moving alpha particle would be deflected by the proton as they Positive like in charge proton, Ruther ford didn't expect to see large deflection. But!!! on the basis of his experiment , he made following observations.

1) Most of the particle (nearly 99%) passed through the foil.

2) A few particle were deflected by foil at very small angles.

3)Very few particle ( 1 in 12000) could not pass the foil and suffered large deflection or even deflected in opposite direction.

From these observation , Rutherford concluded :

1) Since most of the "alpha particle" passed undeflected , the atom is extremely hollow.

2)Since a few "alpha particle" suffered strong deflections and even deflected back at an angle 180° the centre of the atom is a heave and positively charged part that can repel the heavy positively charged Alpha particle.So this part was named the nucleus of atom.

3)Since very few particle undergo deflection ,therefore, the volume of the nucleus  is very small as compared to the total volme of the atom. The radius of the atom is about 10-10m while that of the nucleus is 10-15..

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