What is a mole? A mole is the amount of anything that contains 6.02 x 1023 elementary particles of that thing. That number 6.02 x 1023 is Avogadro's Number, officially the number of carbon-12 atoms found in exactly 12 grams of carbon-12. The mole as a unit of measurement gives scientists a consistent method to convert between the micro- and the macro-, that is, between atoms/molecules and grams. Moles provide a very convenient way to express the amounts of substances involved in chemical reactions.
Why celebrate Mole Day? This year's theme for National Chemistry Week is "Chemistry -- Our Health, Our Future!" and highlights how chemistry improves our well-being in nutrition, medicine, and many other areas. A central and universal unit of measurement, the mole, that helps scientists improve our well-being is certainly well worthy of celebration.