-
300
Democritus
Democritus was an ancient Greek philosopher who lived from 460 BC to 370 BC. He was an influential pre-Socratic philosopher and pupil of Leucippus, who formulated what is thought to be the first atomic theory. -
Period: 300 to
Atomic Theory
-
Antoine Lavoisier
Antoine-Laurent de Lavoisier was a French nobleman and chemist central to the 18th-century Chemical Revolution and a large influence on both the histories of chemistry and biology. He is widely considered to be the "Father of Modern Chemistry." -
Law of Conservation of Mass
Matter cannot be created or destroyed in an isolated system. -
John Dalton
John Dalton FRS was an English chemist, meteorologist and physicist. He is best known for his pioneering work in the development of modern atomic theory, and his research into colour blindness. -
Dalton's Atomic Theory
The theory that matter consists of indivisible particles called atoms and that atoms of a given element are all identical and can neither be created nor destroyed. -
Dimitri Mendeleev
Dmitri Ivanovich Mendeleev was a Russian chemist and inventor. He formulated the Periodic Law, created his own version of the periodic table of elements. -
Cathode Ray Tube
high-vacuum tube in which cathode rays produce a luminous image on a fluorescent screen, used chiefly in televisions and computer terminals. -
Plum Pudding Atomic Model
In 1897 J.J. Thomson discovered the electron, a negatively charged particle more than two thousand times lighter than a hydrogen atom. -
JJ Thomson
Sir Joseph John "J. J." Thomson, OM, FRS[1] (18 December 1856 – 30 August 1940) was a British physicist. In 1897, Thomson showed that cathode rays were composed of a previously unknown negatively charged particle, and thus is credited with the discovery and identification of the electron. -
Robert Millikan
Robert A. Millikan was an American experimental physicist honored with the Nobel Prize for Physics in 1923 for his measurement of the elementary electronic charge and for his work on the photoelectric effect. -
Rutherford Model
In 1909 Ernest Rutherford conducted what is now a famous experiment where he bombarded gold foil with alpha particles (Helium nuclei). A source which undergoes alpha decay is placed in a lead box with a small hole in it. -
Henry Moseley
Henry Gwyn Jeffreys Moseley was an English physicist. Moseley's outstanding contribution to the science of physics was the justification from physical laws of the previous empirical and chemical concept of the atomic number. -
Niels Bohr
Niels Henrik David Bohr was a Danish physicist who made foundational contributions to understanding atomic structure and quantum theory, for which he received the Nobel Prize in Physics in 1922. -
Bohr Planetary
The Bohr Model is probably familar as the "planetary model" of the atom illustrated in the adjacent figure that, for example, is used as a symbol for atomic energy (a bit of a misnomer, since the energy in "atomic energy" is actually the energy of the nucleus, rather than the entire atom). -
Gold Foil Experiment
The Geiger–Marsden experiment was an experiment to prove the structure of the atom performed by Hans Geiger and Ernest Marsden. -
Ernest Rutherford
In early work he discovered the concept of radioactive half-life, proved that radioactivity involved the transmutation of one chemical element to another, and also differentiated and named alpha and beta radiation. -
Quantum Mechanical Model
The Rutherford planetary model of the atom is often what sticks in students’ minds. It provides a neat and familiar picture of electrons orbiting a central nucleus like planets around the Sun. -
Erwin Schrodinger
Erwin Rudolf Josef Alexander Schrödinger was an Austrian physicist who developed a number of fundamental results in the field of quantum theory, which formed the basis of wave mechanics. -
James Chadwick
Chadwick was born in 1891 in Manchester, England. He was graduated from Manchester University in 1911 and remained to work with Ernest Rutherford. -
Electron Cloud Model
The electron cloud model is an atom model wherein electrons are no longer depicted as particles moving around the nucleus in a fixed orbit.
