Please explain in detail the Rutherford's scattering experiment?

Please explain in detail the Rutherford's scattering experiment?


1 Answers

Gaurav Sharma
19 Points
13 years ago

Rutherford’s Scattering Experiment

Ernest Rutherford found some unusual results when he fired very small charged alpha particles at some very thin gold foil. The majority of these particles passed straight through the gold as that there wasn’t any gold. A very few deflected slightly. Very few particles reflected back off the foil.  Rutherford answer to this was a new model of the atom. He suggested that most of the mass of each atom was concentrated in a very small positively charged nucleus at the centre of the atom. The rest of the atom was actually empty space except for electrons circulating around the nucleus at various levels.  The conclusion came from this is that atom is mostly empty space, with a small dense centre of positive charge.

The nucleus is at the centre of the atom and contains the protons and neutrons. Protons and neutrons are collectively known as nucleons.

No of protons = ATOMIC NUMBER of the atom                                                                                                                                                                           No of protons + no of neutrons = MASS NUMBER of the atom    

•    Electron:  negatively charged
•    Proton: positively charged mass of 1 atomic mass unit (1 amu)
•    Neutron: neutral particles

Rutherford proposed that almost all of the positive charge was concentrated in a small region in the center of the atom.  He called it the nucleus.

1 amu = 1/12 atomic mass of carbon 12 (12C)

1 mole = 6.023 x 1023 (Avogadro’s number) atoms or molecules

1 amu/atom (or molecule) = 1 g/mol

Proton: - A proton is a sub atomic particle which has mass nearly 1 amu and a chare of +1 unit (+1.602 *  10 -19).  Mass of Proton = 1.672*10-27 kg.

Electrons :- An electron is a sub atomic particle which carries charge -1.602*10-19 coulomb and has a mass 9.1*10-28 g. i.e., 1/1837th mass of the hydrogen atom.

Neutrons: - A neutron is a sub atomic particle which has a mass of 1.675*10-24 g, or nearly equal to mass of proton or hydrogen atom and carrying no electron charge.


On the basis of scattering experiments, Rutherford proposed a model of the atom which is known as nuclear atomic model. According to this model:-

•    An atom consists of a heavy positively charged nucleus where all the protons and neutrons are present.
•    The volume of the nucleus is very small and is only in minute fraction of the total volume of the atom. Nucleus diameter of the order of 10-12 to 10-13 cm and the atom has diameter of the order of 10-8 cm.
•    There is an empty space around the nucleus called extranuclear part. The number of electrons in an atom is always equal to number of protons present in the nucleus. The volume of the atom is about 1015 times the volume of the nucleus.
•    Electron revolves around the nucleus in closed orbits with high speeds. The centrifugal force acting on the revolving electrons is being counter balanced by the force of attraction between the electrons and nucleus.

Drawbacks of Rutherford Model

•    According to classical electromagnetic theory, when a charged particle moves under the influence of attractive force, it loses some energy continuously in the form of electromagnetic radiation. As a result of this the electron should lose energy at every turn and move closer and closer to nucleus following a spiral path. But it does not happen so.
•    As the revolving electron is losing energy continuously, the atom should emit electromagnetic waves over a continuous range. But experimentally, it was found that every atom emits discrete radiations of particular frequencies/wavelengths only. Thus, the observed spectra of elements cannot be accounted for by Rutherford's atom model.

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