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Democritus develops idea about atoms
He asked this question: If you break a piece of matter in half, and then break it in half again, how many breaks will you have to make before you can break it no further? Democritus thought that it ended at some point, a smallest possible bit of matter. He called these basic matter particles, atoms. -
John Dalton does epierements on Chemicals
John Dalton performed experiments with various chemicals that showed that matter, indeed, seem to consist of elementary lumpy particles (atoms). Although he did not know about their structure, he knew that the evidence pointed to something fundamental. -
J.J. Thomoson Discovers Atom and proposes model
In 1897, the English physicist J.J. Thomson discovered the electron and proposed a model for the structure of the atom. Thomson knew that electrons had a negative charge and thought that matter must have a positive charge. His model looked like raisins stuck on the surface of a lump of pudding. -
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. -
Ernest Rutherford Expierement
He fired energetic a [He2+] particles at a foil, and measured the deflection of the particles as they came out the other side. He found that most of the a’s he shot at the foil were not deflected at all. They passed through the foil and emerged undisturbed. Occasionally, however, particles were scattered at huge angles. -
Neils Bohr
Niels Bohr applies quantum theory to Rutherford's atomic structure by assuming that electrons travel in stationary orbits defined by their angular momentum. This led to the calculation of possible energy levels for these orbits and the postulation that the emission of light occurs when an electron moves into a lower energy orbit. -
James Chadwick
he proved the existence of neutrons - elementary particles devoid of any electrical charge. In contrast with the helium nuclei (alpha rays) which are charged, and therefore repelled by the considerable electrical forces present in the nuclei of heavy atoms, this new tool in atomic disintegration need not overcome any electric barrier and is capable of penetrating and splitting the nuclei of even the heaviest elements. -
Werner Heisenberg & Erwin Schrodinger
Austrian physicist Erwin Schrodinger formed a model of a complete atom as interacting waves. The particles became like vibrations on a violin string, only they were closed in circles. His partial differential equation seemed to bear a similar relation to the mechanics of the atom as Newton's equations of motion bear to planetary astronomy.
