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John Dalton
John Dalton created the very first atomic theory. Dalton was an English school teacher who performed many experiments on atoms. Dalton viewed atoms as tiny, solid balls. His atomic theory had 4 statements listed here. Atoms are tiny, invisible particles. Atoms of one element are all the same. Atoms of different elements are different. Compounds form by combining atoms. -
J.J. Thomson
J.J. Thomson discovered electrons. He was the first scientist to show that the atom was made of even smaller things. He also proposed the existence of a (+) particle. His atomic model was known as the "raisin bun model". Atoms are made mostly out of (+) charged material, like dough in a bun. The (-) charged electrons are found inside of the (+) dough. -
Ernest Rutherford
Rutherford discovered protons and the nucleus. He showed that atoms have (+) particles in the center, and are mostly empty space. He called these (+) particles protons. He called the center of atoms the nucleus. His experiment consisted of shooting proton particles through a sheet of gold. Most particles went through the gold. The atom is mostly empty space. The atom had a very dense (+) center. Rutherford called it the nucleus. -
Niels Bohr
Niels Bohr improved on Rutherford's model. He proposed that electrons should move around the nucleus in specific layers, or shells. Every atom has a specific number of electron shells. -
James Chadwick
Chadwick discovered neutrons. Working with Rutherford, he discovered particles with no charge. He called those particles neutrons. Neutrons are also found in the nucleus. -
Murray Gell-Mann
Murray Gell-Mann discovered quarks, which are any of a number of subatomic particles carrying a fractional electric charge, postulated as building blocks of the hadrons. Quarks have not been directly observed, but theoretical predictions based on their existence have been confirmed experimentally.
