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400
Democritus
In 430 B.C , Democritus proposed the first idea of the atom. The atomic theory stated that “The universe is composed of two elements: the atoms and the void in which they exist and move.” -
Period: 400 to
Atomic Theory Timeline
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Isaac Newton
Proposed a mechanical universe with small solid masses in motion. -
LaVoisier
LaVoiser discovered what is known as the Law of Conservation of Mass which states that matter is conserved in a chemical reaction. Atoms are neither created or destroyed, but it can be rearranged. -
Proust
He published his Law of Definite Proportions that a compound is composed of exact proportions of elements by mass regardless of how the compound was created. -
John Dalton
John Dalton pictures atoms as tiny, indestructible particles, with no internal structure. -
J.J Thomson
A british scientist, discovers the electron, leading to his "plum-pudding" model. He pictures electrons embedded in a sphere of positive electric charge. -
Hanataro Nagaoka
A Japanese physicist, suggests that an atom has a central nucleus. Electrons move in orbits like the rings around Saturn. -
Ernest Rutherford
States that an atom has a dense, positively charged nucleus. Electrons move randomly in the space around the nucleus. -
Niels Bohr
In his model, the electrons move in spherical orbits at fixed distances from the nucleus. -
Louis de Broglie
Proposed that moving particles like electrons have some properties of waves. Within a few years, evidence is collected to suport this idea. -
Erwin Schrodinger
Develops mathematical equations to describe the motions of electrons in atoms. His work leads to the electron cloud model. -
James Chadwick
A british physicist who confirmed that the existence of neutrons, which have no charge. Atomic Nuclei contain neutrons and positively charged protons. -
Lise Meitner, Hahn, Strassman
Conducted experiments verifying that heavy elements capture neutrons and form unstable products which undergo fission. This process ejects more neutrons continuing the fission chain reaction. -
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.
