Avogadro's number

Avogadro's number, also called Avogadro's constant (NA) is a large constant used in chemistry and physics. Avogadro's number is formally defined as the number of carbon-12 atoms in 12 grams (0.012 kg) of carbon-12, which is approximately 6.022 × 1023. Historically, carbon-12 was chosen as the reference substance because its atomic mass could be measured particularly accurately.

History

Avogadro's number is named after the early 19th century Italian scientist Amedeo Avogadro.

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It appears that Jean Baptiste Perrin was the first to name it.

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Perrin called it "Avogadro's constant" and it is still sometimes known by that name. The numerical value was first calculated by Johann Josef Loschmidt in 1865 using the kinetic gas theory. In German-speaking countries, the number may still be referred to as Loschmidt's number. Unfortunately, in a few cases (mainly in the older literature) Loschmidt's number refers to the number of atoms (or molecules) in a cubic centimeter, a usage now disparaged, viz: http://gemini.tntech.edu/~tfurtsch/scihist/loschmid.html

Related Topics:
Johann Josef Loschmidt - 1865 - Kinetic gas theory

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