[http://www.nist.gov/public_affairs/images/04PHY014_HipHopAtomSurfc_HR.jpg]

Democritus (450 BC)

• Everything is made up of small particles called “atomos”.

• These particles were indivisible.

[http://faculty.washington.edu/smcohen/320/Democritus.jpg]

Dalton’s Atomic Theory (1807)

• Elements are composed of atoms.

• Atoms of a specific element are identical.

[http://www.kjemi.uio.no/software/dalton/graphics/john_dalton.gif]

Dalton’s Atomic Theory (1807)

• Atoms are not created or destroyed in reactions.

• A compound always has the same combination of atoms

[http://wps.prenhall.com/wps/media/objects/602/616516/Media_Assets/Chapter02/Text_Images/FG02_02.JPG]

The Electron

• Benjamin Franklin (mid-1700’s)

• (+) and (-) charges exist.

• Did not know where they came from.

[http://www.npl.co.uk/publications/electricity/images/kite.gif]

The Electron• Cathode Ray Tube

or CRT (mid-1800’s)

• “Beam” traveled from positive to negative end of tube.

[http://members.chello.nl/~h.dijkstra19/image/burning%20ray%20tube.jpg]

Click Here for a CRT Video

[http://wps.prenhall.com/wps/media/objects/602/616516/Media_Assets/Chapter02/Text_Images/FG02_03.JPG]

[http://www.cheniere.org/images/Magnet%20on%20TV.jpg]

The Electron

• Thompson’s “Plum Pudding Model” (1896)

• Light is not moved by a magnet, so the “light” in the CRT must be charged particles in atoms.

Radioactive Particles• Becquerel & Curie (1896)

• Certain elements emit both negative and positive particles

Radioactive Particles

• Rutherford’s Gold Foil Experiment.

• Shot radioactive particles at a thin piece of gold.

Click here for video of actual results

Radioactive Particles

• Rutherford concluded that all the positive charges of an atom would be contained in the middle or nucleus.