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404 BCE
Democritus
lived from 460BC to 370bc.Discovered atomic theory-everything composed of atoms and are physically,not geometrically indivisible.Said in between atoms is empty space,atoms always have been and always will be in motion,there is infinite number and kinds of atoms.Found by experiment that takes seashell and breaks it in half to powder.Took smallest piece of powder, found it couldn't break anymore.Nickname was Laughing Philosopher.First to propose evidence based atomic theory -
John Dalton
Lived from 1766-1844 in the UK.Dalton’s atomic theory proposed that all matter was composed of atoms which are indivisible&indestructible.While all atoms of an element were identical,different elements have atoms of differing size&mass.His experiments on gases are what led to the Dalton’s Law Dalton was born into a Quaker family&started working as a teacher at 12 -
J.J. Thompson
Lived from December 18, 1856 to August 30, 1940 in the UK. He discovered the electron in 1897 by experimenting with a cathode ray. He demonstrated that cathode rays are negatively charged and also studied positively charged particles in neon gas. He was awarded the Nobel Prize in Physics in 1906 for the discovery of the electron. He proposed the plum pudding model of the atom in 1904 before the discovery of the atomic nucleus to be able to include the electron in the atomic model. -
Robert Millikan
Lived from march 22, 1868 to december 19, 1953 and lived in the united states. Was credited with discovering the value of electron charge through the oil drop experiment in 1909. The oil drop experiment was where they put tiny charged droplets of oil between 2 metal electrodes and balanced downward gravitational force with electric forces and upward drag. He received the Nobel Prize for physics in 1923 for his study of the photoelectric effect and the elementary electric charge. -
Ernest Rutherford
Born August 30 1871 died October 19, 1937. Rutherford’s theory suggested that there was a very compact and concentrated area of the atom that contained most of the atomic mass of the particle. This was deemed the Nucleus. He proved this by using something called the Gold Foil Experiment. This experiment involved bouncing particles off gold foil. He realized a small amount deflected while the other passed through. Rutherford concluded that the center of the atom held most of the atomic mass. -
Niels Bohr
Niels Bohr was a Danish-born physicist born on October 7, 1885, and died November 18, 1962. Bohr proposed that the electrons within the atom orbit the atomic nucleus, but can jump from one energy orbit to another. He also discovered that the number of electrons and electron orbits around the nucleus determines the properties of the element. -
Erwin Schrodinger
Lived from August 12, 1887 to January 4, 1961 in Austria. He explained the movement of electrons in an atom (Wave Mechanics) By using the de Broglie equation he combined the equations for the behavior of waves to generate a mathematical model for the distribution of electrons in an atom. First to explain the movement of electrons with visuals and the second to explain the idea. Was awarded the Nobel prize in physics, Erwin Schrodinger Prize,and the Austrian Decoration for Science and Art. -
James Chadwick
Born October 20, 1891. Died July 24, 1974. He was born and lived in England.He proved the existence of neutrons. These particles are neither positive or negatively charged. He also discovered that these neutrons still greatly contribute to the atomic weight of the atom.Studied under Rutherford at the time of his discovery. He was knighted in 1945. Won Nobel Peace Prize.
