History of The Atom

460 BC Democritus develops the idea of atoms

He pounded up materials in his pestle end martar until he had reduced them to smaller and smaller particles which he called

ATOMA

(greek for indivisible)

1808 Jhon Dalton

Suggested that all matter was made up of tiny apheres that were able to bounce around with perfect elasticity and called them

ATOMS

Download Dalton Atomic Theory

1898 Joseph Jhon Thompson

Found that atoms could eject a for smaller negative which he called on

ELECTRON

1904

Thompson develops the idea that an atom was made up of electrons scattered unevenly with in an elastic sphere surrounded by a soup of positive charge to balance the electron’s charge like plums surrounded by pudding

PLUM PUDDING MODEL

Download JJ Thompson's Model and Alpha Particle Scattering

1910 Ernest Rutherford

Oversaw Geiger and Marsden carrying out his famous experiment They fired Helium nuclei at a plece of gold foil which was only a few atoms thick They found that atthough most of them passed through. About 1 in 10000 hit.

They found that while most of the helium nuclei passed through the foil, a small number were deflected and, to their surprise, some helium nucled bounced straight back.

Rutherford’s new allowed him to propose a more detailed model with a central nucleus.

He suggested thet the positive charge was all in a central nucleus. With this holding the electrons in place by electrical attraction.

However, this was not the end of the story.

1913 Niels Bohr

Studied under Rutherford at the Victoria University in Manchester

Bohr refined Rutherford’s idea by adding that the electrons were in orbits. Rather like planets orbiting the sun. With each orbit only able to contain a set number of electrons. 

Helium Atom

What do these particles consist of? 

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