Avogadro's Number

The concept of the mole is intimately twined with Avogadro’s number, a mathematical constant estimated to be (6.022 * 1023). This figure, used as a conversion factor from grams to atomic mass units, corresponds to the number of carbon-12 atoms in twelve grams of carbon—that is, a mole of carbon atoms. It is also used to define a mole of other substances, a unit of amount that corresponds to (6.022 * 1023) particles of that substance, whether the particles are atoms, molecules, quasars, or peanuts. The vastness of Avogadro’s number results macrocosmic amounts of the substance in question. Thus, a mole of soda cans would cover the entire breadth of the United States to a depth of more than two hundred miles (Johnson).

The magician of a number’s history is perhaps as mysterious as its strange mathematical powers. Though it bears the name of Italian scientist Amedeo Avogadro, it was first calculated by the Austrian chemist and physicist Johann Josef Loschmidt. Thus, one may occasionally hear it referred to Loschmidt’s number despite that fact that another mathematical constant once bore that name, though that usage has now fallen out of favor (“Avogadro’s”). The German “Loschmidt'sche Zahl” has always been the preferred name for this number in Loschmidt’s birthplace and its surrounding countries.

The numerical value of Avogadro’s number was first estimated in 1865. Loschmidt applied principles of liquid density, gaseous viscosity, and the kinetic gas theory, particularly Avogadro’s discovery that “any gas under the same conditions has the same number of molecules per mole” (“Johann”). Reasoning from those ideas, he was able to determine the number of molecules in one cubic centimeter of gas and used this to derive the estimation (Johnson).

Since Loschmidt’s groundbreaking attempt to estimate the value of Avogadro’s number, contemporary efforts have yielded more accurate results. The preferred modern method requires a crystal and uses its density, atomic mass, and unit cell length, as determined by x-ray methods (Johnson).

Whether calculated by a nineteenth century theorist or in a modern laboratory pulsing with x-rays, Avogadro’s number is proved invaluable to chemists. In converting from grams to particles and from particles to moles, it allows scientists to explore the properties of atoms and other such particles. “What it does demonstrate is how small an atom or molecule is compared to the amounts of material we are familiar with in everyday life, since the definition of the mole involves amounts of material we are completely familiar with” (Johnson).


Works Cited

“Avogadro’s Number.” Wikipedia, the Free Encyclopedia. 20 October 2004. Wikimedia Foundation, Inc. 22 October 2006. http://en.wikipedia.org/wiki/Avogadro%27s_number.

“Johann Josef Loschmidt.” Wikipedia, the Free Encyclopedia. 15 September 2006. Wikimedia Foundation, Inc. 22 October 2006. http://en.wikipedia.org/wiki/Johann_Josef_Loschmidt.

Johnson, Chris. “Amedeo Avogadro.” Chris Johnson’s Blot on the Net. 4 July 2004. 22 October 2006. http://www.bulldog.u-net.com/avogadro/avoga.html.

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