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100
Democritus
400 BC
'grandfather' of the Atomic Theory because he recognized that atoms exsisted and were mechanically bound -
100
Aristotle
Said that there were 4 elements, earth, water, fire, and air. Believed in reasoning instead of scientific experiments and said democritisus' atom theory wasn't right. -
Antoine Lavoisier
established the Law of Conservation of Mass
suggested that element cannot be broken down into simpler components and combined elements would create chemical compounds. -
John Dalton
father of modern atomic theory • 5 parts to theory • includes elements are composed of atoms • also includes elements atoms are identical in mass -
John Dalton
Atomic theory proposed by John Dalton
Dalton's theory was based on the premise that the atoms of different elements could be distinguished by differences in their weights. -
JJ Thomson
Beginning in 1895 physicist J. J. Thomson theorized that cathode rays produced in Crookes' tubes must be composed of what he called "corpuscles", a single type of negatively charged particle. -
Joseph John Thomson
discovered electron
• described nature of cathode rays
• plum pudding model of atom- Joseph John Thomson proposed that the atom was a sphere of positive electricity (which was diffuse) with negative particles imbedded throughout after discovering the electron, a discovery for which he was awarded the Nobel Prize in physics in 1906. -
.Robert Millikan
measured charge of an electron • oil drop experiment • completed with Thomson -
Max Planck
atoms can emit quanta • Einstein used Plancks work to study photons -
Period: to
Timeline
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Gold Foil Experiment
Ernest Rutherford's experiment that showed that atoms are mostly emppty space except for the nucleus -
Niels Bohr
model of the atom
electrons travel in specified energy levels
• spectrum lines produced when electrons move
• introduced that electrons orbit around the nucleus in an atom -
Ernest Rutherford
gold foil experiment • atom has small positive nucleus, remainder is empty space • predicted existence of neutrons -
Louis deBrogile
• electrons have properties of both waves and particles • group of waves named after him -
Hans Geiger
demonstrated that
mass and energy are conserved in the
atomic process -
Erwin Schrodinger
showed mathematically that waves can be used to describe electrons in atoms • determined probability location of electrons in atoms -
Werner Heisenberg
• uncertainty principle
• impossible to determine the position
and the momentum of a particle at the same time
• cloud model aka quantum mechanical mode -
James Chadwick
helped with the development of the nuclear model and discovered neutron -
Glen Seaborg
•Succeeded in making man-made elements. •won the 1951 Nobel Prize in Chemistry for "discoveries in the chemistry of the transuranium elements", contributed to the discovery and isolation of ten elements