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Democritus
He was the first to use the term atom and proposed that atoms were mechanically bound. It seemed to him that if atoms stayed together they did it with a system like a hook and eye. While we know that this is not true, he was very far ahead of his time by acknowledging the existence of the atom and many people consider him the father of modern science for his contributions. -
John Dalton
He discovered that certain gases only could be combined in certain proportions even if two different compounds shared the same common element or group of elements. -
J.J. Thomson
In 1897, Thomson was the first to suggest that the fundamental unit was over 1000 times smaller than an atom, putting forth his theory of the sub-atomic particles now known as electrons. -
Hantaro Nagaoka
Nagaoka rejected Thomson's model on the ground that opposite charges are impenetrable. He proposed an alternative model in which a positively charged center is surrounded by a number of revolving electrons, in the manner of Saturn and its rings. -
Niels Bohr
Bohr introduced the idea that an electron could drop from a higher-energy orbit to a lower one, in the process emitting a photon of discrete energy. This became a basis for quantum theory. -
Ernest Rutherford
Rutherford overturned Thomson's model in 1911 with his well-known gold foil experiment in which he demonstrated that the atom has a tiny, massive nucleus. Rutherford designed an experiment to use the alpha particles emitted by a radioactive element as probes to the unseen world of atomic structure. -
James Chadwick
Chadwick discovered the nuetron in 1932. -
Werner Heisenberg and Erwin Schrodinger
The electron cloud model is an atom model where electrons are no longer shown as particles moving around the nucleus in a constant orbit.
