ATOMIC THEORY TIMELINE

DEMOCRITUS

DEMOCRITUS

• Democritus broke a seashell in half until he could not make it smaller.
• He had a theory that everything is composed of "atoms."
• He did not make a model for this experiment or theory.

ARISTOTLE

ARISTOTLE

• Aristotle did not do an experiment, nor did he make a model.
• He believed in the elements.
• Everything was composed of either earth, water, fire, or air.

DALTON

DALTON

• John dalton calculated various atomic weights.
• He discovered that all atoms have the same mass in the same element.
• Different atom masses=different element.

THOMSON

THOMSON

• Thomson used positive rays to seperate atoms.
• He discovered that atoms can be divided.
• He used a model called the "plum pudding model."

RUTHERFORD

RUTHERFORD

• Discovered radioactivity.
• Also discovered that there is a nucleus in atoms. (Only solid part of atom.)
• Shot rays through beryllium.
• Saw which ones went through and which bounced off. Then asked "why?"

MILIKAN

MILIKAN

• Conducted the "oil drop experiment."
• Discovered electron charges. (Pos. and Neg.)
• Named protron and electron.

CHADWICK

CHADWICK

• Used a thin sheet of beryllium with alpha particles.
• Neutrons have the same mass as proton which allowed masses to mstch.
• Discovered the most recent model of the atom.

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