-
400
Democritus
Youtube Video
In 400 B.C. Democritus, who was not a scientist but a philosopher, stated that matter was composed of tiny particles. He decided that these particles should be called "atomos," which later gave us the name, atom. Atomos originally meant indivisible. He thought that if you broke something down again and again, eventually it could not be broken down any further. Click the link. -
Period: 400 to
Atom Timeline
-
Antoine Lavoisier
Lavosier's Life and Discovery
Antoine Lavoisier came up with the Law of Conservation of mass after observing the fact that a chemical change in a sealed container did not alter the mass of its contents. He concluded that matter was neither created nor destroyed, it only changed form. Click the link to learn more about Lavoisier's other achievements. -
Joseph Proust
Law of Definite Proportion
Joseph Proust was a French chemist who figured out that the elements that compose a compound are always in found in the same proportions no matter the amount of the element. He called this concept the, Law of Definite Proportion. -
John Dalton
Dalton's Atomic Theory
Dalton developed an atomic theory and some of the concepts are still used today. His atomic theory had four parts.
1. Matter is composed of indivisible particles called atoms.
2. Atoms that are of the same element are identical, atoms of one element are not the same as atoms from another element.
3. Matter cannot be created or destroyed. (Law of Conservation of Mass)
To see the fourth part watch the video. -
J. J. Thomson
Plum Pudding Model
1895 - 1897
J. J. Thomson is credited for the discovery of electrons and also isotopes. Thomson was awarded the 1906 Nobel Prize in Physics for the discovery of the electron and his other research involving gases. -
Robert Andrews Millikan
Oil Drop Experiment
1909 - 1911
Millikan conducted the Oil Drop Experiment and determined the charge of a single electron. Coupled with J. J. Thomson's charge-to-mass ratio, he was able to determine the mass of a single electron as well. -
Ernest Rutherford
Gold Foil Experiment
1909 - 1911
Rutherford is most famously known as the conductor of the Gold Foil Experiment which proves that atoms are mostly consisted of empty space with only a small dense nucleus. He also "split the atom" and discovered the concept of a half-life in radioactivity. -
James Chadwick
Discovery of the Neutron
Chadwick is responsible for discovering the neutron. He concluded that something caused the atom to have more mass, but did not alter the charge.
