Models of the Atom
Overview
Until the early 1900s, the laws of classical physics, established in the seventeenth century by Isaac Newton (1642-1727) and in the nineteenth by James Clerk Maxwell (1831-1879), described the behavior of objects in the everyday world well. But investigations into the structure of the atom began to turn up strange phenomena that the Newtonian picture of the universe could not explain. The succession of atomic models put forth in the first part of the twentieth century reflect the attempts of scientists to understand and predict the weird behavior observed at tiny scales.
Background
It was the Greek philosopher Democritus who in 460 B.C. wondered what the smallest possible particles of matter might be and called them "atoms." At the beginning of the twentieth century, however, no one had yet proved that atoms really existed. All of that changed when a Swiss patent clerk named Albert Einstein (1879-1955)published a theoretical paper that established the existence of atoms once and for all.
In 1827, peering into his microscope, the Scottish botanist Robert Brown (1773-1858) noticed that a grain of pollen floating in a drop of water jiggled about in a random way. In 1905 Einstein developed a mathematical formula for this so-called "Brownian motion," arguing conclusively that it was due to the pollen grains colliding with unseen atoms.
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