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460 BCE
Democritus 460-370 b. C.
Matter is composed of atoms, which move though an empty space.
Atoms are solid, homogenous, indestructible, and invisible.
In greek, atomos means indvisible. -
384 BCE
Aristotle 384-322
Empy space cannot exist.
Matter is made of earth, fire, air and water.
Aristotle denied the atom's existence -
Lavoisier
The law of conservation of mass.
He used the scientific method -
Joseph Proust
Law of definite proportions -
Dalton
He developed the atomic theory:
matter is composed of extremely small particles called atoms
atoms are invisible and indestructible.
atoms of a given element are identical in size, mass, and chemical properties. -
Joseph Thomson
He identifies the electron
The electron has a negative charge.
Plum pudding model. -
Ernest Rutherford
He discovered the atomic nucleus ass well as the proton with its positive charge.
Experiment of the gold leaf, which concluded that an atom consists of empty space through which electrons move. -
Niels Bohr
He publishes a theory of atomic structure, associating the electron arrangement in atoms and atomic chemical properties, winning Nobel prize in 1922.
He assigned a quantum number to each orbit -
Erwin Schrodinger
Quantum mechanical model.
Each orbit has energy associated with it. -
Werner Heisenberg
The uncertainty principle:
"The more precisely position is determined, the less precisely the momentum is known in this instant, and vice versa" -
James Chadwick
He proved the existence of neutrons
