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Period: 370 to 460
Democritus
Democritus's theory stated that:
All matter consists of atoms.
Atoms are invisible, indestructible, homogeneous, and can’t be destroyed.
Atoms differ in size. -
400
Democritus's Atomic Theory
Democritus's atomic theory states that:
All matter consists of atoms.
Atoms are invisible, indestructible, homogeneous, and can’t be destroyed.
Atoms differ in size. -
John Dalton's Atomic Theory
John Dalton's Atomic Theory states:
All matter consists of atoms.
Atoms are invisible and indestructible.
All atoms of a given element are identical in mass and properties.
Compounds are formed of two or more atoms.
A chemical reaction is a rearrangement of atoms. -
J.J. Thomson's Atomic Theory
J.J Thomson identified the negatively charged electron. He also calculated the charge to mass ratio of an electron.e/m = -1.76 x 108 coulombs/g
He proposed the plum pudding atomic model. -
Robert Milliken's Atomic Theory
He determined the charge of an electron with his Oil Drop Experiment(1909), which helped calculate the mass of an electron and positively charged particles. -
Ernest Rutherford's Atomic Theory
He proposed the nuclear atom as a result of the gold-foil experiment. He discovered that positive charge and mass are found in the small center of the atom while the majority of the volume is occupied by electrons. in 1920, he first referred to the hydrogen nucleus as a proton and proposed the neutron. -
Neils Bohr's Atomic Theory
He discovered that electrons travel in their own separate orbits.
An electron's orbit size is determined by its energy. -
James Chadwick's Atomic Theory
Officially discovered the neutron in 1932.
