Askjagden's Guide to Chemistry: the Atomic Theory
Along with his teacher, Leucippus, Democritus, a Greek philosopher, proposed the idea of atomism and stated that all matter consisted of tiny and indivisible particles, which he termed atomos. Although he was rejected by well-known up-to-date philosophers like Plato, Democritus' teachings were surprisingly accurate in terms of 19th century research.
In 1803, John Dalton, an English scientist, mathematician, and school teacher stated his "atomic theory," which is currently one of the most fundamental and central ideas in chemistry. The atomic theory stated:
1. An element, which is a pure substance that can't be simplified chemically, are made of only one type of atom.
2. Atoms that compose the same element are identical in all properties, including size, mass, and chemical qualities. The atoms of other elements have differing properties.
3. Compounds are structures composed of more than one element, or, more specifically, atoms of different elements. Those atoms combine in whole-number or a simple fraction ratios.
4. A chemical reaction doesn't create or destroy; it only combines, separates, and rearranges atoms.
Dalton also proposed a second hypothesis: the law of multiple proportions. Sometimes named Dalton's law or Dalton's theory, the law of multiple proportions states that when two elements combine to make one compound, then the ratio of one element's to the other's, which is kept fixed, which basically means to be kept constant, or the same throughout, are in ratios of small whole numbers. For example, take carbon monoxide, or CO, and carbon dioxide, or CO_2. However, there isn't a molecule called CO_1.3.
Dalton proposed a third hypothesis: the law of conservation of mass, which states that matter is neither created nor destroyed. (Not only matter, but also energy, which also has mass. During a chemical reaction, sometimes the form of matter may change, but the amount will always remain the same. Sometimes energy will be converted, sometimes as heat. But once again, the net matter and energy will always be constant.
Dalton, of course, wasn't the only contributor to the atomic theory. In 1799, Joseph Proust published his law of definite proortions. This law stated that even if there were different samples of the same compound, the ratios of elements would be constant. For example, if there were 1 gram of water, the ratio from oxygen to hydrogen would be 1:2. If there were 2 grams of water, the ratio would still be 1:2.
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