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According to J.J. Thomson, the electron is a constituent of all matter. It has a negative charge of 1.602 × 10-19 C and a mass of 9.1085 × 10-31 kg at rest. Electrons are distributed along with positive charges in the atom in a sphere of radius 10-10 m like a plum in the pudding. Atom is electrically neutral as there is an equal number of positive and negative charges.
Failure of Thomson’s Atom Model
In this experiment, α-particles are emitted by some radioactive material (polonium) R, kept inside a thick lead box. This well-collimated beam is then allowed to fall on the gold foil F. while passing through the gold foil, the α-particles are scattered through different angles. The scattered α-particles are in a particular direction are allowed to strike on a screen coated with zinc sulphide. When a α-particle is incident on zinc sulphide, it produces fluorescence and is detected with the help of the microscope M.
Rutherford’s Atomic Model
On the basis of α-particle scattering experiment, Rutherford suggested his atomic model
Drawbacks of Rutherford’s Atom Model
Manu Kumar Khatry, Manoj Kumar Thapa, Bhesha Raj Adhikari, Arjun Kumar Gautam, Parashu Ram Poudel.Principle of Physics. Kathmandu: Ayam publication PVT LTD, 2010.
S.K. Gautam, J.M. Pradhan. A text Book of Physics. Kathmandu: Surya Publication, 2003.
Atom is electrically neutral as there is an equal number of positive and negative charges.
An atom consists of a positive nucleus in which entire positive charge and almost whole mass of the atom are concentrated.
The size of the nucleus is of the order of 10-15 m which is small compared to the size of the atom (10-10 therefore the nucleus occupies only a small portion of the available space.
In this experiment, α-particles are emitted by some radioactive material (polonium) R, kept inside a thick lead box.