![]() ![]() The best estimate of the charge on an electron based on modern experiments is 1.60217653 x 10 -19 coulombs per electron. The best estimate of the value of a Faraday, according to the National Institute of Standards and Technology (NIST), is 96,485.3383 coulombs per mole of electrons. The charge on a mole of electrons had been known for some time and is the constant called the Faraday. This became possible for the first time when American physicist Robert Millikan measured the charge on an electron. In the years since then, a variety of techniques have been used to estimate the magnitude of this fundamental constant.Īccurate determinations of Avogadro’s number require the measurement of a single quantity on both the atomic and macroscopic scales using the same unit of measurement. In 1909 Perrin reported an estimate of Avogadro’s number based on his work on Brownian motion-the random movement of microscopic particles suspended in a liquid or gas. The term “Avogadro’s number” was first used by French physicist Jean Baptiste Perrin. This quantity is now known as the Loschmidt constant, and the accepted value of this constant is 2.6867773 x 10 25 m -3. In 1865 Loschmidt used kinetic molecular theory to estimate the number of particles in one cubic centimeter of gas at standard conditions. The first person to estimate the actual number of particles in a given amount of a substance was Josef Loschmidt, an Austrian high school teacher who later became a professor at the University of Vienna. Avogadro is most famous for his hypothesis that equal volumes of different gases at the same temperature and pressure contain the same number of particles. Avogadro was a lawyer who became interested in mathematics and physics, and in 1820 he became the first professor of physics in Italy. ![]() Contrary to the beliefs of generations of chemistry students, Avogadro’s number-the number of particles in a unit known as a mole-was not discovered by Amadeo Avogadro (1776-1856).
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