Ernest Rutherford

Ernest Rutherford

Ernest Rutherford publishes his atomic theory describing the atom as having a central positive nucleus surrounded by negative orbiting electrons. This model suggested that most of the mass of the atom was contained in the small nucleus, and that the rest of the atom was mostly empty space. Rutherford came to this conclusion following the results of his famous gold foil experiment. This experiment involved the firing of radioactive particles through minutely thin metal foils (notably gold) and detecting those using screens coated with zinc sulfide (a scintillator). Rutherford found that although the vast majority of particles passed straight through the foil approximately 1 in 8000 were deflected leading him to his theory that most of the atom was made up of 'empty space'.

1) Most of the positively charged “bullets” passed right through the gold atoms in the sheet of gold foil without changing course at all.

2) Some of the positively charged “bullets,” however, did bounce away from the gold sheet as if they had hit something solid. He knew that positive charges repel positive charges.

3) This could only mean that the gold atoms in the sheet were mostly open space. Atoms were not a pudding filled with a positively charged material.

4) Rutherford concluded that an atom had a small, dense, positively charged center that repelled his positively charged “bullets.”

5) He called the center of the atom the “nucleus”

6) The nucleus is tiny compared to the atom as a whole.

7) Rutherford reasoned that all of an atom’s positively charged particles were contained in the nucleus. The negatively charged particles were scattered outside the nucleus around the atom’s edge

Merit and demerit of Rutherford’s model

Merit

1) Electrons move fast through the atom.

2) Electrons are trapped within the atom by a positively charged nucleus

3) Electrons are negatively charged.

Demerit

1) Failed to discover the nucleus contains positively charged particles called protons

2) Failed to discover the nucleus also contains neutrons (a sub atomic neutral particle

Limitation of Rutherford’s model

1) Rutherford’s model was compared with the solar system in which planets revolve around the sun in fixed circular paths.....but there is an important difference between the two .firstly whereas the electron and the nuclei are the microscopic particles, sun and planets were big bodies and hence Newtonian law of motion do not apply to the motion of microscopic particles..(There is a separate branch called quantum mechanics for microscopic particles)

2) secondly sun and planets do not carry any charge like electrons and nuclei according to Maxwell's electromagnetic theory whenever a charged particle like electron is revolving in a field

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