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460
Democritus
"by convention bitter, by convention sweet, but in reality atoms and void" Everything is made of atoms which are indivisible and indestructible. Between atoms lies empty space and atoms are always moving. He also found that there are an infinite number of atoms which are different shaped are sized. He described how natural phenomena's occurred because of the interaction and/or movement of atoms. -
Period: 460 to
Atomic Theory
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Isaac Newton
Isaac Newton introduced the laws on gravitation, atoms were held together by attractions called forces. He adapted atomism to fit the concept of God’s role in creation. Light was also composed of some kind of atoms and solar rays were to be streams of particles. -
John Dalton
Development of modern atomic theory. Atoms of an element were the same as its weight, the atoms of different elements had different weights and atoms combined in small whole-number ratios to form compounds. -
George Johnstone Stoney
Calculation of the magnitude of the atom or particle of electricity which he introduced as the electron and suggested the idea that particle or atom of electricity is one of three fundamental units on which a whole system of physical units can be established.
Introduced the term 'electron' in 1891 but introduced the concept as early as 1874. -
Joseph John Thomson
discovery of the electron and proposed that the electrons were distributed throughout a sea of positively charged particles and thus invented the plum pudding model which was later found to be untrue by E. Rutherford. proposed that the electrons were distributed throughout a sea of positively charged particles like plums were distributed throughout a plum pudding -
Max Planck
established the quantum theory in which energy can only be absorbed or radiated in discrete values or quanta.
Oscillating atoms absorb and emit energy in bundles only. -
Hantaro Nagaoka
Proposed that the atom nucleus was large and positively charged and electrons that orbited the nucleus were bound by electrostatic forced.
Developed an incorrect "Saturnian" model of the atom with flat rings of electrons revolving around a positively charged particle based on his fascination on the planet, Saturn.
Proved that electrons moving around the nucleus were bound by electrostatic forces- like gravitational pull keeping the rings of Saturn revolving. -
Robert Andrews Millikan
Found the charge of an electron through the oil-drop experiment and found the charge of the electron to be 1.592 × 10−19 coulomb. -
Ernest Rutherford
He devised the Rutherford model, which is a model of the atom where there was a central charge surrounding by orbiting particles. He also made the discovery of protons and suggested the idea of neutrons in the nucleus. -
Henry Gwyn-Jeffreys Moseley
Arranged the Periodic Table in order of the atomic numbers of the elements. He introduced law that outlines that the ''square root of the frequencies of lines in atomic x-ray spectra depends linearly on the atomic number of the emitting atom.'' -
Niels Bohr
Made the Bohr model of the atom which showed that electrons moved in specific orbits and the shell model of the atom in which an element’s chemical properties are determined by the number of electrons in the outermost orbit.This also showed why electrons are stable in an atom. -
James Chadwick
Proved the existance of neutrons through Frederic and Irene Joliot-Curie’s experiment that he saw to find particle radiation. It's mass was 0.1% more than that of the proton's and it was found to have a neutral charge.
