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400 BCE
Democritus
Democritus, discovered atom around 400 B.C.E . , He was an Greek philosopher that thought that all matter is composed of indivisible elements -
Lavoisier
Lavoisier, established the law of conservation of mass, determined that combustion and respiration are caused by chemical reactions with what he named “oxygen,”
Between 1772 and 1794 -
Dalton
Dalton discovered that, The total pressure of a mixture of gases amounted to the sum of the partial pressures that each individual gas exerted while occupying the same space. In 1803 -
Eugen Goldstein
In 1886 Eugen Goldstein discovered what he termed Kanalstrahlen, or canal rays, also called positive rays; these are positively charged ions that are accelerated toward and through a perforated cathode in an evacuated tube. -
Becquerel
Becquerel, a French physicist who discovered radioactivity through his investigations of uranium and other substances.Henri Becquerel was well positioned to make the exciting discovery, which came just a few month after the discovery of x-rays. -
J.J Thomson
On April 30, 1897, British physicist J.J. Thomson announced his discovery that atoms were made up of smaller components. In 1903 he introduced the plump pudding model. -
Rutherford
Rutherford discovered radon in 1900 , radon was an radioactive element
He found that the atom consists mostly of empty space, with its mass concentrated in a central positively charged nucleus -
Planck
Max Planck was a German theoretical physicist who discovered the quantum of action, now known as Planck's constant, h, in 1900 -
Millikan
In 1910 Robert Millikan succeeded in precisely determining the magnitude of the electron`s charge. Small electrically charged drops of oil were suspended between two metal plates where they were subjected to the downward force of gravity and the upward attraction of an electrical field. -
Bohr
Bohr discovered that a model of the atom in which the electron was able to occupy only certain orbits around the nucleus in 1913. He also stated that, electrons could only occupy particular orbits determined by the quantum of action and that electromagnetic radiation from an atom occurred only when an electron jumped to a lower-energy orbit. -
de Broglie
1924 Louis de Broglie introduced the idea that particles, such as electrons, could be described not only as particles but also as waves. -
Schrodinger
Erwin Shrodinger described how electrons move in wave form, and developed the Schrodinger equation which describes how the quantum state of a system changes with time. He discovered in 1926 -
Heisenberg
In february 1927 , Werner heisnberg developed a key piece of quantum theory. Werner Heisenberg contributed to atomic theory through formulating quantum mechanics in terms of matrices and in discovering the uncertainty principle. In 1925, Werner Heisenberg formulated a type of quantum mechanics based on matrices. In 1927 he proposed the "uncertainty relation", setting limits for how precisely the position and velocity of a particle can be simultaneously determined. -
james chadwick
Chadwick is best known for his discovery of the neutron in 1932. A neutron is a particle with no electric charge that, along with positively charged protons, makes up an atom's nucleus.