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Jan 1, 1000
Democritus discovers atoms
In 3800 BC, Democritus wondered whether things could be divided into smaller pieces forever. He decided they could not, and named the smallest piece possible the “atom,” meaning “not to be cut.” -
Dalton Researches and Experiments with Atoms
In 1803, he concluded that evaporated water exists in air as an independent gas. He wondered how water and air could occupy the same space at the same time, when obviously solid bodies can't. If the water and air were composed of discrete particles, Dalton reasoned, evaporation might be viewed as a mixing of water particles with air particles. -
Crookes Researches and Experiments with Atoms
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Thomson Researches and Experiments with Atoms
In 1894, Thomson used a CRT to experimentally determine the charge to mass ratio (e/m) of an electron =1.759 x 108 coulombs/gram. -
Becquerel Researches and Experiments with Atoms
He knew that fluorescent substances glow in the dark. In 1896, he devised an experiment to find out if fluorescent substances would give of x-rays. He wrapped photographic film in light-proof paper. Then he placed uranium salt on top of the paper. He left these materials in direct sunlight to cause the uranium to become fluorescent. -
Rutherford Researches and Experiments with Atoms
He identified the atom as having a central positive nucleus surrounded by negative orbiting electrons. This model suggested that most of the mass of the atom was contained in the small nucleus, and that the rest of the atom was mostly empty space. Rutherford came to this conclusion following the results of his famous gold foil experiment. This experiment involved the firing of radioactive particles through minutely thin metal foils (notably gold) and detecting them using screens coated wit -
Bohr Researches and Experiments with Atoms
He based his theory of the new atomic model upon rutherford's original "plum-pudding" model. He did no specific experiments. -
Chadwick Researches and Experiments with Atoms
In this experiment, alpha particles are projected towards beryllium target. The emitted particles are allowed to fall on paraffin wax, which in turn releases another type of particles. The study of the properties of such particles showed that they are protons. From the energy calculations, Chadwick showed that the particles released from beryllium, as a result of the incidence of alpha particles on it, are uncharged and have the same mass as protons. He called them neutrons. -
The Current Atom
The current model of the atom is Bohr's atomic model.
