Atomic models

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Dalton and Thompson


19th century: -Atoms are solid spheres

                   -Different spheres make up different elements


1897: -Plum pudding model

         -Atom must contain smaller, negativley charged particles (electrons)

        -'solid sphere' idea had to be changed

        -Electrons spread evenly like plum pieces in a pudding.

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Rutherfords model

1909 Golden Foil experiment

-Fired positivley charged alpha particles at a very thin sheet of gold

-From the plum pudding model, it was expected that the positive particles would be deflected slightly, however most of the particles passed straight through, proving the plum pudding model to be wrong.

Nuclear model of the atom

-Designed by Rutherford after his experiment

-Tiny, positivley charged nucleas in the middle, surrounded by a 'cloud' of electrons

-Much of the atoms is empty space.

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Bohrs Model

Rutherfords proved wrong as the 'cloud of electrons' would spiral down and cause the atom to collapse.

Niels Bohrs model proposed:

-Electrons only exist in orbital shells.

-Each shell has a fixed energy

-When an electron moves between shells, electromagnetic radiation is emitted or absorbed.

-Radiation will have a fixed frequency because energy of shells is fixed.

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