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Democritus
Democritus discovered the atom, a particle that could not be cut. He said that atoms were small, hard particles and were made up of a single material formed into different shapes and sizes. His model was called Democritus Model. -
Dalton
Dalton wanted to know why elements combine in certain proportions to form compounds so he experimented with different substances. His results were that
-all substances are made of atoms
-atoms of the same element are alike, and atoms of different elements are not
-atoms join with other atoms to make new substances
His model was called the Billiard Ball. -
Thomson
J.J. Thompson found that there are small particles inside the atom, proving Dalton's theory slightly wrong. He experimented with a cathode-ray tube, discovering that a positive plate attracted a beam, which was made of particles with negative charges, which he after discovered are in every atom. He called these electrons. Thomson's model was called Plum -Pudding. -
Rutherford
Rutherford tested Thomson's theory by doing an experiment to study the parts of the atom. He aimed a beam of particles with a postive charge at a sheet of gold foil, expecting the particles to pass through, but to his surprise, some were deflected or bounced back. His model was called the planetary model. -
Bohr
Niel Bohr discovered that electrons move in an orbit shell determined by the chemical properties of other elements. His model was Bohr's model. -
Chadwick
James Chadwick contributed to the atomic theory by discovering the neutron and that it helps reduce the rettraction between protons and won't stabilize the nucleus. His model was called Chadwick Model.