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400 BCE
Democritus
Born: 460 BCE
Died: 370 BCE.
Interesting fact: Democritus was a wealthy heir and believed to have spent his inheritance on travelling so that he could learn from other cultures’ scholars. -
400 BCE
Democritus' Atomic Model
He stated that atoms are minuscule quantities of matter making up all things. Democritus had a thought experiment. The idea was if you took a material and divided it half, you would have a smaller but identical chunk. If you keep dividing your material, there should eventually be a point where you've reached the smallest representative element of your material. That element is the “atom". -
John Dalton's Atomic Model
He stated that all things are made up of atoms, and atoms cannot be split into smaller pieces. He also said that all atoms of the same element are exactly alike, nut different elements are made up of different atoms. All substances are made of atoms. Atoms join together to form compounds, and a given compound always consists of the same kinds of atoms in the same proportions. Dalton thought individual atoms were solid, hard spheres, so he modeled them with wooden balls. -
John Dalton
Born: September 6, 1766
died: July 27, 1844
Interesting Fact: John Dalton did not start school until he was 12. -
Joseph John "JJ" Thomson
born: December 18, 1856
died: August 30, 1940
Interesting Fact: He was knighted in 1908. He was elected Fellow of the Royal Society in 1884 and was President during 1916-1920; he received the Royal and Hughes Medals in 1894 and 1902, and the Copley Medal in 1914. -
JJ Thomson's Atomic Model
Thomson was the first person to propose the idea of negatively charged electrons and unknown positive charges. Thompson thought the atom was a sphere of positive charge, but negatively charged electrons were spread evenly among the positive charge. He said that if the atom had more positive mass, the atom would be positively charged, and if the atom had more negativity charged electrons the atom would be negatively charged. -
Robert Andrews Milikan
Born: March 22, 1868
Died: December 19, 1953
Interesting Fact: Millikan was an enthusiastic tennis player, and golf was also one of his recreations. -
Robert Milikan's Atomic Model
He discovered accurate determination of the charge carried by an electron, using the elegant “falling-drop method”; he also proved that this quantity was a constant for all electrons, thus demonstrating the atomic structure of electricity. -
Ernest Rutherford
born: August 30, 1871
died: October 19, 1937
Interesting Fact: He liked cars and his hobby was playing golf -
Ernest Rutherford's Atomic Model
Rutherford said that the atom has an atomic nucleus containing protons and neutrons. He also stated that the electrons go around the nucleus in a electron orbit, but he died before he could prove his theory. Ernest Rutherford found that the atom is mostly empty space, with nearly all of its mass concentrated in a tiny central nucleus. The nucleus is positively charged and surrounded at a great distance by the negatively charged electrons. -
Niels Henrik David Bohr
Born: October 7, 1885
Died: November 18, 1962
Interesting Fact: Niels Bohr was born and raised in Copenhagen -
Niels Bohr's Atomic Model
In 1913, Niels Bohr proposed a theory for the hydrogen atom, based on quantum theory that some physical quantities only take discrete values. Electrons move around a nucleus, but only in prescribed orbits, and If electrons jump to a lower-energy orbit, the difference is sent out as radiation. -
Werner Karl Heisenberg
Born: December 5, 1901
Died: February 1, 1976
Interesting Fact: As a child he played the piano, and had a remarkable ability to play complex compositions despite his age. -
Werner Heisenberg
Heisenberg developed a mathematical way of expressing the energy levels of electrons in atoms. His theory states that there is uncertainty in measuring such features of a particle as the position and momentum of an electron are hard to predict. -
Erwin Rudolf Josef Alexander Schrodinger
Born: August 12, 1887
Died: January 4, 1961
Interesting Fact: Schrodinger was awarded the Nobel Prize for physics in 1933 for his work on what is known as the Schrodinger equation -
Erwin Schrodinger's Atomic Model
Based on de Broglie's idea that particles could exhibit wavelike behavior, Erwin Schrödinger theorized that the behavior of electrons within atoms could be explained by treating them mathematically as matter waves. -
Sir James Chadwick
Born: October 20, 1891
Died: July 24, 1974
Interesting Fact: During WWII he also helped develop the Atomic Bomb -
James Chadwick's Atomic Model
James Chadwick discovered that atoms consisted not only of protons and electrons but also neutrons. Chadwick discovered the neutron, a neutral subatomic particle that has approximately the same mass as a proton. Neutrons occupy the nucleus of the atom
