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440 BCE
Democritus
He discovered Atoms, naming them Atomos. Atomos- "uncuttable", the smallest particles of matter. Atoms are made of a single material formed into different shapes and sizes. They are small, hard particles. -
John Dalton
Believed all substances were made of atoms. Atoms of the same element are exactly alike. Atoms made of different elements were different/had different properties (specifically weight). He conducted experiments in combining elements and wanted to know why elements combine in specific proportions. Believed compounds were made up of a certain ratio of elements. In a chemical reaction the number stays the same, it isn't created or destroyed. -
J.J. Thompson
He discovered the small negatively charged particles inside an atom through his cathode-ray tube experiment.His theory of atomic structure led to the "plum-pudding" model. This is because his theory stated that there are negative charges in a sphere of a positive charge. The "plum-pudding" model could be changed to the "cookie dough" model for a more current analogy. -
Rutherford
He conducted the Gold Foil experiment which made him discover the small, dense positively charged nucleus when 1/8000 positive particles bounced back from the gold foil. He found that atoms contain mostly empty space and that most of an atom's mass is in the nucleus. His atomic model had electrons surrounding the nucleus at a distance. -
Niels Bohr
He found that electrons travel in certain paths, or energy levels. Electrons can jump from a path in one level to a path in another level. -
Werner Heisenberg
Unlike Bohr, Heisenberg found that electrons are found in electron clouds, not paths. He found that electron paths cannot be predicted. They don't travel in orbits, just certain regions. This is the Uncertainty Principle. -
Erwin Schrodinger
He began to think about explaining the movement of an electron in an atom as a wave. This what he called Wave Theory. -
James Chadwick
When working as Rutherford's assistant, he discovered another particle in the nucleus of atoms. It was the neutral Neutron. He won the 1935 Nobel Prize. He also advanced the work of nuclear fission and the model of the atom.
