Atoms and their structure

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Some drops would hover

Slide 25

Millikan’s Experiment

From the mass of the drop and the charge on

the plates, he calculated the charge on an electron

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Rutherford’s Experiment

Ernest Rutherford English physicist. (1910)

Believed the plum pudding model of the atom was correct.

Wanted to see how big they are.

Used radioactivity.

Alpha particles - positively charged pieces given off by uranium.

Shot them at gold foil which can be made a few atoms thick.

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Rutherford’s experiment

When the alpha particles hit a florescent screen, it glows.

Here’s what it looked like (pg 72)

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Lead block

Uranium

Gold Foil

Flourescent

Screen

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He Expected

The alpha particles to pass through without changing direction very much.

Because…

The positive charges were spread out evenly. Alone they were not enough to stop the alpha particles.

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What he expected

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Because

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Because, he thought the mass was evenly distributed in the atom

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Because, he thought the mass was evenly distributed in the atom

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What he got

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How he explained it

Atom is mostly empty.

Small dense, positive piece at center.

Alpha particles are deflected by it if they get close enough.

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Slide 37

Modern View

The atom is mostly empty space.

Two regions.

Nucleus- protons and neutrons.

Electron cloud- region where you might find an electron.

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Density and the Atom