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400 BCE
Democritus
His mentor, Leucippus, originally came up with the atomic theory, but it was then adopted by Democritus. -
350 BCE
Aristotle
All matter composed of 4 elements, earth, air, fire, water. -
Antoine Lavoisier
Recent invention of balance, he did a lot of quantitative measurement. Lead him to law of conservation of mass- states mass cannot be created nor destroyed. Mass of reactants will equal mass products. -
Joseph Proust
He first published his Law of Definite Proportions, this says that the law states that the same elements in exactly the same proportions by mass -
John Dalton
English chemist school teacher. Law of multiple proportions- if compounds of the same elements, the masses of the elements can be expressed as ratios of whole numbers.
1. All matter is composed of extremely small particles
2. Atoms of a given element are identical in size, mass, & other properties, atoms of different elements differ in size
3. Atoms cannot be divided,created,or ruined
4. Atoms combine in whole # ratios to form
5. Atoms are combined, separated, or rearranged in chemical reactions -
JJ Thomson
credited with the discovery and identification that the electron had a negative charge. chocolate chip cookie -
Robert Millikan
oil drop experiment, figured out mass of electrons -
Ernest Rutherford
gold foil experimen, nucleus- very small & very dense. positive charge part was a proton -
Niels Bohr
The discoveries of the electron and radioactivity at the end of the 19th century led to different models for the structure of the atom -
Schrodiner & Heisnberg
physicists were trying to apply Planck's concept of energy quanta to the atom and its constituents -
James Chadwick
worked with rutherford, discovered the neutron