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400 BCE
Democritus
1.) All elements are composed of atoms
2.)Atoms of the same element are identical
3.0Atoms of different elements combine in simple whole-number ratios to form chemical compounds. -
John Dalton
Gases that first became possible at the turn of the nineteenth century led John Dalton in 1803 to propose a modern theory of the atom based on the following assumptions. 1. Matter is made up of atoms that are indivisible and indestructible. -
Eugene Goldstein
He was an early investigator of discharge tubes, the discoverer of anode rays, and is credited with the discovery of the proton. -
J.J Thomson
He created the Plum pudding model -
Robert Millikan
Robert Millikan was a physicist who discovered the elementary charge of an electron using the oil-drop experiment. -
Ernest Rutherford
The nuclear structure of the atom discovered alpha and beta rays and proposed the laws of radioactive decay -
Niels Bohr
It is a system consisting of a small, dense nucleus surrounded by orbiting electrons—similar to the structure of the Solar System, but with attraction provided by electrostatic forces in place of gravity. -
James Chadwick
Bombarded beryllium atoms with alpha particles. Unknown radiation was produced. Chadwick interpreted this radiation as being composed of particles with a neutral electrical charge and the approximate mass of a proton. -
Dmitri Mendeleev
It is the ninth transuranium element of the actinide series discovered. It was first identified by Ghiorso, Harvey, Choppin, Thompson, and Seaborg in early in 1955 during the bombardment