| Themes > Science > Physics > About Physics, Generalities > A Brief History and Philosophy of Physics > The Development of Classical Physics: Mechanics, Heat, Optics, Electromagnetism, Atoms > Atoms |
Until the twentieth century, the development of the atomic theory of matter was pursued by scientists who are often more closely identified with chemistry than with physics. In 1789 Antoine Lavoisier published his Elements of Chemistry. In this work, he emphasized the need for quantitative methods in chemistry. By carefully devised experiments, he was able to isolate 23 elements, fundamental substances that could not be broken down into simpler forms. In England in the late 1700s, the experimentalists Joseph Black, Henry Cavendish and Joseph Priestley isolated several different gases and showed how they could be produced. Schneer makes the interesting point that a large number of the most successful scientists of this era, including Priestley, Dalton, Faraday, James Watt (who greatly improved the steam engine), Thomas Young, and Franklin, were all Quakers, a non-conforming religious group who dared to challenge the established beliefs of the day. Then in 1802 John Dalton, an English schoolmaster, revived the theory of atoms. It was known by this time that gases always combine in fixed ratios by mass. For example one gram of hydrogen burns with eight grams of oxygen to produce nine grams of water. Dalton proposed that these ratios of whole numbers could be explained if the gases were formed of atoms whose masses were, themselves, in the ratio of simple integers. The formation of water discussed above could then be explained by the combination of two hydrogen atoms with one oxygen atom. At this time, Dalton was unaware that both hydrogen and oxygen gas consisted of "molecules" which were each composed of two atoms, but his theory was correct in essence. In 1869 Dimitri Mendeleev of Russia, combining Dalton's atomic description with the fact that certain groups of elements had similar chemical properties, constructed the first periodic table. He pointed out that the gaps in this table should correspond to as-yet-undiscovered elements, and was able to predict their properties and atomic masses. Armed with this knowledge, scientists very quickly discovered most of the missing elements. |
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