-
300
Aristotle (384-322 BC)
Discovered four "elements"- earth, fire, air, water
Believed in reasoning instead of scientific experiments
Dismissed Democritus' atom idea was "worthless" -
400
Democritus of Adbera (460 BC- 370 BC)
Atomos- indivisible
First to identify possibility of an atom
Smallest piece of matter -
John Dalton (September 6, 1766- July 27, 1844)
Father of modern atomic theory
5 parts of theory
Includes elements are composed of atoms
Also includes element's atoms are identical in mass -
Joseph John Thomson (December 18, 1856- August 30, 1940)
Discovered electron
Described nature of cathode rays
Plum pudding model of atom -
Max Planck (April 23, 1858- October 4, 1947)
Atoms can emit "quanta"
Einstein used this scientist's work to study photons -
Robert Millikan (March 22, 1868- December 19, 1953)
measured charge of an electron
oil drop experiment
completed with Thomson -
Ernest Rutherford (August 30, 1871- October 19, 1937)
Gold Foil experiment
Atoms has small positive nucleus, remainder is empty space
Predicted existence of neutrons -
Neils Bohr (October 7, 1885- Novemeber 18, 1962)
Planetary model of atom
Electrons travel in specified energy levels
Spectrum lines produced when electrons move -
Louis deBroglie (August 15, 1892- March 19, 1987)
Showed mathematically that waves can be used to describe electrons in atoms
Determined probability location of electrons in atoms -
Erwin Schrolinger (August 12, 1887- January 4, 1961)
Electrons have properties of both waves and particles
Group of waves named after this scientist -
Werner Heisenberg (December 5, 1901- February 1, 1976)
"uncertainty principle"
impossible to determine the position and the momentum of a particle at the same time
"cloud" model aka quantum mechanical model -
James Chadwick (October 20, 1891- July 24, 1974)
Helped with the development of the nuvlear model
Also discoevered the "neutron"
