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Quantization
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Although classical physics treated substances as being continuous, philosophy and logic dictated that this could not really be true. Even the ancient Greeks reasoned that if a person took a substance and divided it into smaller and smaller parts, a point must eventually be reached where the substance could no longer be divided and still retain its original characteristics. They called this smallest unit of matter the atom. Today we say that matter is quantized. In fact, not only is matter quantized, but so is energy, electrical charge, angular momentum, and many other properties associated with matter and energy.
But at the turn of the twentieth century, quantization was still a mystery. Nevertheless, certain important experiments began to shed light on the phenomenon. For example, Millikan’s oil drop experiment demonstrated that the electrical charge of an electron was quantized with a value of –e = –1.6x10-19 C. When this was combined with J. J. Thomson’s earlier e/m experiment, scientists knew that the mass of the electron was quantized with a value of me = 9.1x10-31 kg. Chemistry experiments demonstrated that the most elemental chemicals could be arranged in a periodic table, that they combined in integer ratios according to a number called their valence, and that the net chemical charge was zero. This meant that the electrical charge on the smallest units of chemistry (the atoms) were quantized in units of +e. Fariday’s law of electrolysis then showed that the mass of the atom was quantized in atomic mass units u = 1.66x10-27 kg. Conversely, this showed that the number of molecules per mole of a substance was a constant called Avogadro’s number NA = 1/u = 6.023x1026 molecules/kmole = 6.023x1023 molecules/mole.
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