Question:   What is a mole?  I hear about it a lot, but I don't understand what it means.

Answer:

Let's recap with something that's familiar:

What's a "pair"?  It's two things.  What kind of things?  Anything!  If you've got two shoes, you have a pair.  If you have a pair of glasses, you have two pieces of glass stuck in a frame.  If you have two birds, you've got a pair of them.

What's a "dozen"?  It's twelve things.  What kind of things?  Anything!  If you've got a dozen eggs, you've got 12 eggs.  If you've got a dozen cans of soda, you have twelve.  It doesn't matter what those things are, you've still got a dozen.

What's a "mole"?  It's 6.02 x 10²³ things.  What kind of things?  Anything!  If you've got 6.02 x 10²³ bowling balls, you've got a mole.  If you've got 6.02 x 10²³ cats, you've got a mole of cats.  Moles are no different than pairs or dozens, except that the number is a whole lot bigger.

You've probably also noticed that moles are really important in chemistry.  The reason for this is that a "mole" is a handy unit for measuring molecules and atoms in the real world.  If I tell you that I've got 602000000000000000000000 atoms, that's not something you can easily grasp.  However, if I say I've got a mole, that's a much easier thing to imagine.

So, if moles are so important, why haven't you heard of them before?  The reason is simple:  Most things you see in everyday life are too big to ever collect a mole in one place.  For example, I've heard it said that a mole of M&M candies would cover the continental United States approximately 120 km deep in candy.  That's a lot of stuff.  As it turns out, the only thing that you can really get a mole of very easily are atoms and molecules - the reason being that they're so small.  A mole of water molecules, for example, easily fit in the palm of your hand.