The Atomic Theory

Democritus

Jan 1, 1000

said that matter could not be infinitly divided.made the term atomos to describe the tiny particals floating in space.

Aristole

Jan 2, 1001

Disagreed with Democritus’ idea that atoms move through empty spacedenied the existence of atoms due to ideas about nature.
His ideas about matter took over those of Democritus back to square one.

john dalton

Aug 1, 1808

English schoolteacher who marks the beginning of the development of modern atomic theory.
Took Democritus’ ideas about matter and revised them based off of his personal scientific research.
Revived the term “atom”
“Atoms are the smallest particles of matter and are indivisible and indestructible.”

sir william crookes

Jun 17, 1832

noticed a green flash of light within a cathode ray tube while working in a dark laboratory. Some type of radiation striking a zinc-sulfide coating inside the tube. this discovery lead to the telivision.

Ernest Rutherford

Sep 10, 1871

• explained that the negatively-charged electrons were held within the atom by the positively-charged nucleus.
•The nucleus must also be extremely dense, because it contains the majority of the mass of the atom.
•proved the plum pudding model of the atom was wrong.

James Chadwick

Sep 10, 1891

• demonstrated that the nucleus had another neutral subatomic particle, the neutron
•Neutrons are subatomic particles that carry no electric charge and weighs just about the same as a proton.

J.J. thompson

Jan 1, 1897

discovered electron its mass and charge. disproved Dalton’s theory that atoms were indivisible. Thompson received the Nobel Prize in 1906 for his research—the discovery of the electron, the first subatomic particle.

Robert Millikan

Jan 1, 1909

designed an oil drop apparatus to determine the charge of the electron. Determined that the magnitude of the electron. Discovered the mass of the electron using the known charge/mass ratio: 9.1x10-28 g