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I almost forgot. It’s National Chemistry Week here in the U.S., including the annual celebration of National Mole Day. (NPR had coverage too.)

Mole Day (October 23rd, or 10/23 as we write here in the States), celebrates a key concept in chemistry: Avogadro’s number, which defines a mole of particles. 6.02 × 10²³

I’d like you to try out an experiment for me. Pour yourself a glass of water. I’ll wait.

OK, see that glass of water? I don’t know exactly how much, but you probably poured out around 10²⁴ molecules of water (H₂O).

A mole of water weighs about 18 grams. Not a lot of mass, but it’s a small molecule. But if it’s a huge number of molecules. To give you some idea how many, here are a few examples:

• There are between 6-7 billion people in the world. If I had a mole of pennies ($0.01), each person would have approximately $1 trillion worth of pennies.
• Put another way, since there are about 6-7 billion people in the world, there are approximately a mole of human cells on this world. (Not counting animals, plants, insects, bacteria…)
• Wikipedia points out that a mole of sand would cover the entire U.S. to a depth of about a centimeter (or slightly less than half an inch).

All of this goes to show that chemistry really involves using extremely small things like atoms and molecules in vast numbers like moles. More amazing is that we can actually calculate to reasonable accuracy how many atoms and molecules we’re using.