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RUTHERFORD THEORY

Lenard’s Experiment

Lenard’s experiment was meant to proof that if Thomson’s atomic model is right, electrons that go through the aluminum plate should’ve experienced energy loss, so the electrons should be easily refracted.

In Lenard’s experiment, he shows that Thomson’s atomic model is wrong because he found that most of the electrons were not refracted. This shows that electrons are not spread evenly.

Continuation of Lenard’s Experiment

In 1911, Ernest Rutherford was interested to continue Lenard’s experiment by replacing electrons with a particle which consist of positive charge. This experiment was conducted by Hans Geiger & Ernst Marsden.

Who is Ernest Rutherford?

He is a New Zealand-born, British chemist and physicist. In 1914, he was knighted and two years later, he was awarded the Hector Memorial Medal. Under him, Nobel Prizes were awarded to James Chadwick for discovering neutron. Rutherford remains the only science Nobel Prize winner to have performed his most famous work after receiving the prize.

Rutherford’s research

• a “rays” / particles • Theory of protons• Detector for electromagnetic waves

What are a rays / particles?

• High speed particles• Made up of two protons and two neutrons• Is a nucleus, same as the nucleus of a common

atom of helium• Don’t have electrons around it• Type of ionizing radiation• will loose all their energy in just a couple

inches of travel in air

What Rutherford did?

He directed the a rays to a gold plate surrounded by screen coated with sulfide zinc which are around the plate.

What happened?

1. Some of the a particles pass the empty space go trough

Nucleus

a Particles Atoms of Gold foil

2. Some of the a particles that approach the nucleus are deflected

Nucleus

a Particles

Atoms of Gold foil

3. Some of the a particles that hits the nucleus are bounced back

Nucleus a Particles

Atoms of Gold foil

Conclusion of Rutherford’s Theory

• A large fraction of the room in an atom is empty– Indicated by most of a rays pass through the plate

Nucleus

a Particles Atoms of Gold foil

• Nucleus is tiny yet very dense core of atom– Indicated by little amount of refracted a rays

Nucleus a Particles

Atoms of Gold foil

• Electrons go circle the nucleus with high speed– Indicated by the electrons that are not attracted by

protons inside the nucleus

• The charge of the nucleus is the same as a particle’s, which is positive– Indicated by the deflected rays that deflected due to

repulsion forces of similar charge.

Nucleus

a Particles

Atoms of Gold foil

Rutherford’s Theory Weakness

Based on Rutherford’s theory that states electrons go around the nucleus will stay on its path is unproved. Based on physics classical mechanic law, that objects that going around on circular path will release its energy in the form of radiation, so the electron will be going closer to the nucleus. But then, Rutherford’s theory is supported by Bohr’s theorem.