Timeline of Atomic Theory Contributions

By: Jasmine Parsons

Events

Aristotle

332 BCE

Aristotle believed that all materials on earth was not made of atoms, rath-er a combination of fire, water, air and earth.

Democritus

322 BCE

Democritus hypothesized that the world was made up of particles called atoms. He believed they were indestructible, indivisible, and always in m-otion.

Robert Boyle

1662

Boyle discovered that as volume increases, the pressure of the gas decr-eases in proportion. Similarly, as volume decreases, the pressure of the -gas increases which in sum is what is known as Boyle's Law.

John Priestley

1774

Priestley discovered "dephlogisticated air", which is known as oxygen.

Antoine Lavoisier

1785

He explained combustion and proposed the law of conservation of mass, which was the bases for Dalton's work. His started the conversation of w-hat an atom really was.

Joseph Proust

1794

Proust discovered and stated the Law of Definite Proportions, which allo-wed for the set up of Dalton's theory,

John Dalton

1803

John Dalton's was the first to come up with atomic theory with a four part theory. He believed atoms were invisible particles we couldn't see. He cr-eated a basis for modern atomic theory.

William Crookes

1879

Discovered cathode rays ravel in straight lines from the cathode; impart a negative charge to objects they hit; are deflected by electric fields and m-agnets to suggest a negative charge; cause glass to fluoresce; cause pinwheels in their path to spin showing they have mass.

JJ Thompson

1897

Thomson tested the polarity of atoms and found almost all particles had a negative charge. He also developed the plum pudding model of an atom. He even discovered electrons which were the first subatomic particles to be identified.

Marie Curie

1898

Marie along with Pierre studied radioactive materials. They studied urani-um and thorium and saw a decay process which they named radioactivity.

Pierre Curie

1900

While working on radioactive substances, Pierre discovered gamma rays. He also studied with his wife Marie to discover radioactive elements of p-olonium and radium.

Jean Baptiste Perrin

1908

Perrin Supported Albert Einstein's theory that Brownian motion, the rand-om movement of small particles in a liquid, was because of collisions bet-ween the particles and molecules in the liquid.

Hans Geiger

1909

Geiger developed an electrical device, the Geiger Müller tube that clicks when hit with alpha particles.

Robert Millikan

1909

Millikan performed the oil drop experiment which determined the charge (e=1.602 x 10 -19 coulomb) and mass (m = 9.11 x 10 -28 gram) of electrons.

Ernest Rutherford

1911 - 1917

He came to the conclusion alpha particles are positive, beta particles are negative, and neutral a neutral particle is light.

James Chadwick

1932

James Chadwick showed that a nucleus contains neutrons along with pr-otons.