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340 BCE
Democritus and Leucippus
They stated that matter is composed of atoms separated by empty space through which they move. They also said that atoms are solid and are of different sizes and shapes. -
John Dalton Sept. 6, 1766 - Jul. 27, 1844
He suggested that all matter is made of atoms and that they are indivisible and indestructible. Also, he stated that atoms form the same element are identical. -
Eugene Goldstein Sept. 5, 1850 - Dec. 25, 1930
He discovered there is a ray that travels in the opposite direction of the electron. This was a subatomic positive charge in the atom, called the protons, and he inserted them into the atomic model. -
Joseph John Thompson Dec. 18, 1856 - Aug. 30, 1940
He discovered the electron and said they travel in a staight line in high velocities. The atom was considered a positive charged sphere with little electrons all over this sphere. -
Ernest Rutherford Aug. 30, 1871 - Oct. 19, 1937
Ernest Rutherfor proposed, in his atomic model, that the atom have a nucleus with protons, that have almost the whole mass of the atom, and that there are electrons spinning around it as if it was the planets around the sun. A lot of empty space was left in the atom. -
James Chadwick Oct. 20, 1891 - Jul. 24, 1974
He discovered an neutral charge in the atom. He called this charge a neutron. He stated that neutrons have the same mass as protons. Both protons and neutrons can be find at the nucleus of the atom and the electron is orbiting around them in an empty space. -
Neil Bohr Oct. 7, 1855 - Nov. 18, 1962
Bohr modified the Rutherford model by requiring that the electrons move in orbits of fixed size and energy. He also stated that the energy of an electron depends on the size of the orbit and is lower for smaller orbits.
