Illustration from Kenneth Grahame's "The Wind in the Willows" showing Mole and his friends, Badger, Ratty, and Toad, having a picnic along the river, discussing Avogadro's number
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Oct 23 is "Mole Day," an unofficial holiday celebrated among chemists, chemistry students and chemistry enthusiasts on October 23, between 6:02 AM and 6:02 PM, making the date 6:02 10/23 in the American style of writing dates.
The time and date for this day are derived from Avogadro's number or constant, which is approximately 6.02×10^23, defining the number of particles (atoms or molecules) in the scientific unit known as one "mole" of a substance. The term mole was coined around the year 1900 by the German chemist Wilhelm Ostwald. It comes from the german word for molecule 'molekül'.
Contrary to the beliefs of generations of chemistry students, Avogadro's number was not discovered by Amadeo Avogadro (1776-1856) himself. Avogadro, who was a practicing lawyer, became interested in mathematics and physics and by 1820 became the first professor of physics in Italy. 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.
The term "Avogadro's number" is a more recent one, first used by French physicist Jean Baptiste Perrin.
Accurate 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. This became possible for the first time when American physicist Robert Millikan measured the charge on an electron.
To review the concept of moles, click the friendly mole below.