|Ernest Rutherford, Niels Bohr physics|
J. J. Thomson’s model of the atom—a cloud of electrons like plums in a positively charged pudding— didn’t explain why a few random alpha particles, shot into gold foil—when most passed right through— bounced straight back. Ernest Rutherford realized that the atom had a small and dense center, its nucleus— with a diameter less than one three-thousandth of the atom’s diameter, but over ninety-nine point ninety-four percent of the atom’s mass— which, being positively charged, keeps its electrons orbiting around it, leading Niels Bohr—in explaining the pattern of spectral emissions of helium—to say electrons are confined to concentric spherical shells around the nucleus, and for an electron to jump between shells it must absorb or emit the definite amount of energy associated with the difference of energies between the shells, which explains why atoms emit light in sharply defined spectral lines.
Benefits and liabilities
Atoms plus an understanding of the periodic table gives us chemistry. Atoms plus magnets to move its electrons gives us electricity and electronics. Atoms plus the forces in the nucleus give us the atom bomb. If we understand the parts and how they are put together, then we can take them apart and put them back together in useful ways. Some of these operations require energy, and some release energy. The goal is to control the benefits and to limit the risks, which for most of the effects induces denial whose strength is equal to the anticipated power.
My first-order approximation is a wild and crazy guess. My second-order approximation tries only to make the guess seem less crazy. On further analysis, in some restrictive sense, it might be somewhat true, but if it’s fundamentally flawed then I can see how to change it. I run my third-order approximation through a battery of hypothetical scenarios, each of which may suggest a qualification, a refinement, or an additional guess. Pretty soon, what begins as a form of fun becomes totally unwieldy, like reality.
There have been other models of the atom, including the cubical atom model, which explained bonding between atoms by sharing electrons at corners, and the Saturnian model, where electrons rotate around a positive nucleus like the rings of Saturn. The Bohr model also was not the last, being superceded by the atomic orbital or wave mechanics model, in which the orbits of the electrons are described by the probability equations of quantum theory.
See also in The book of science:
Readings in wikipedia: