Today is a day for celebration in chemistry, but it's a holiday you likely haven't heard of. You see, atoms are very tiny things. This makes them difficult to count, let alone do other calculations with. Less than 100 years ago, scientists were able to come up with a "constant" to use when determining the number of atoms or molecules in a substance: 6.02 x 10^23. This number was termed the "mole," which is Latin for "lump." Think of a mole indicating a fixed number of atoms---like dozen means 12 and gross means 144. This number is also referred to as Avogadro's number, after an Italian scientist (Amadeo Avagadro) who had done some preliminary reasoning about this idea in the 18th century. You can probably tell that a mole is a very big number, but since atoms are small, you don't necessarily have to have a big lump of something to have a mole of it.
Since this number has a great deal of significance for chemistry, it's worth celebrating every October 23 (10^23) from 6:02 (6.02) in the morning to 6:02 in the evening. There's even a Mole Day Foundation to help with themes and ideas.
At my school, we start the day off right. We meet at "Moledonald's" at 6:02 in the morning. Believe it or not we usually get about 125 kids show up. This is more than half of the students taking chemistry. McDonald's now takes initiative and calls us each year to see if we're coming to celebrate---instead of us warning them of the prospective onslaught. We did this on Friday, since Mole Day was going to be on a Sunday this year. It's a great deal of fun.
Students can earn "Mole Bucks" for coming to the kickoff. They can also earn Mole Bucks for their decorated t-shirts, cards, games, and more. Mole Bucks can be used for extra credit throughout the year. At school, there are games such as making the shape of a mole (animal) using a mole of aluminum foil. Last year, the men in my department all wore "mole-lets" (mullets) and jammed out to "Mole Thing" ("Wild Thing") at the school pep assembly.
Perhaps some of this doesn't sound too educational. Maybe it isn't. But it does make everyone enthusiastic about chemistry, which isn't such a bad goal.
So get out there and enjoy Mole Day today!
UPDATE: For those of you who got here by Googling for "mole bucks," I put a sample on my 2006 post.