-
460
Democritus
Democritus developed the theory that the universe consisted of and an almost infinite number of invisible particles. He had the idea that the atom was indivisible. Although he was wrong, he was very close to the truth.
All matter is made of indivisible particles called atoms. -
Period: 460 to
Date
-
Newton
Newton proposed a mechanical universe with small solid masses in motion. He suggested that atoms were held together by attractions, we call forces. -
Dalton
Proposed an "atomic theory" with spherical proposed solid atoms based upon measurable properties of mass. Many unexplained chemical phenomena were quickly explained by Dalton with his theory -
G.J. Stoney
Proposed that electricity was made of discrete negative particles he called electrons. He was first to start the proposal of the standard symbols of elements that we currently use. -
J.J. Thomson
Used a CRT to experimentally determine the charge to mass ratio of an electron. He was te first person to suggest the theory of the atom containing positive and negative particles, and demonstrated the latter which he called electrons. -
Planck
Used the idea of quanta to explain hot glowing matter.
(came up with the quantum theory) -
Nagaoka
Postulated a "Saturnian" model of the atom with flat rings of electrons revolving around a positively charged particle. The model made two predictions which were later successfully confirmed by Rutherford. -
Milikan
He discovered that the weight of an electron is 1836 times smaller than that of a hydrogen atom. -
E.Rutherford
Rutherford proposed that the positive charge must really be localized, concentrated in a small nucleus.
And this led to the planetary model of the atom. -
H.G.J Moseley
Using x-ray tubes, determined the charges on the nuclei of most atoms. His work was used to reorganize the periodic table based upon atomic number instead of atomic mass. -
Bohr
Developed an explanation of atomic structure that underlies regularities of the periodic table of elements. His atomic model had atoms built up of successive orbital shells of electrons. He also helped develop the atomic bomb. -
James Chadwick
Using alpha particles discovered a neutral atomic particle with a mass close to a proton. Thus the neutron was discovered - he was the first person to do so. -
Glenn Seaborg
Synthesized 6 transuranium elements and suggested a change in the layout of the periodic table. -
Enrico Fermi
Conducted the first controlled chain reaction releasing energy from the atoms nucleus. Fermi developed the quantum theory.
