Atomic Structure, History of the Atom

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Slide 1

Atomic Structure

S.MORRIS 2006

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Slide 2

History of the atom

460 BC

Democritus develops the idea of atoms

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

ATOMA

(greek for indivisible)

Slide 3

HISTORY OF THE ATOM

1808

John Dalton

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

ATOMS

Slide 4

HISTORY OF THE ATOM

1898

Joseph John Thompson

found that atoms could sometimes eject a far smaller negative particle which he called an

ELECTRON

Slide 5

HISTORY OF THE ATOM

Thompson develops the idea that an atom was made up of electrons scattered unevenly within an elastic sphere surrounded by a soup of positive charge to balance the electron's charge

1904

like plums surrounded by pudding.

PLUM PUDDING

MODEL

Slide 6

HISTORY OF THE ATOM

1910

Ernest Rutherford

oversaw Geiger and Marsden carrying out his famous experiment.

they fired Helium nuclei at a piece of gold foil which was only a few atoms thick.

they found that although most of them passed through. About 1 in 10,000 hit

Slide 7

HISTORY OF THE ATOM

gold foil

helium nuclei

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

helium nuclei

Slide 8

HISTORY OF THE ATOM

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

He suggested that 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.

Slide 9

HISTORY OF THE ATOM

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.