by CKR
For us chemists, six-point-oh-two-times-ten-to-the-twenty-third is an essential mantra. It's a mole: the number of molecules that make up the a mass of a substance that is equal in grams to the molecular mass of that substance. It's a very, very basic number that we use all the time in figuring out all sorts of things, starting with how much you need of one thing to produce a certain amount of another.
It's historically important because it marks the recognition by Amadeo Avogadro (six-point-oh-two-times-ten-to-the-twenty-third being known as Avogadro's number) that molecules were different from atoms and that both were discrete entities, too small to be seen individually in his time (early nineteenth century), but measurable in the mole mass. Avogadro's number of atoms is called a gram-atom, but I'll include that in the Mole day celebration. Avogadro also recognized something very important about gases: that equal volumes of all gases at the same temperature and pressure contain the same number of molecules. This is called Avogadro's principle, and, like the mole, it is used over and over again by chemists to calculate all sorts of things.
Mole Day is mostly to encourage students with just a bit of humor, some of which some of them will already have discovered in the mole homonym.
And, it can be argued, the concept of the mole and Avogadro's history are some of the basic facts of science that everyone should know.
So happy Mole Day, everyone!