Chemistry: What's a Mole?

What's a Mole?

I'm wearing a pair of shoes right now. My question for you: How many shoes am I wearing? If you're thinking "two," you obviously know your footwear.

Another pop quiz: I'm feeling ill because I just ate a dozen eggs. How many eggs did I eat? If you said "12," you're clearly in tune with the poultry industry.

Molecular Meanings

A mole is equal to 6.02 × 1023 things. Though you could, in theory, have a mole of anything, this number is so huge that we usually only speak of having moles of atoms or molecules, because both are very tiny.

One more pop quiz: If I bought a ream of paper, how many sheets of paper did I purchase? If you said "500," you're ready to become a world-class paper salesman!

So what does all this have to do with the mole? As you're already aware, atoms and molecules are very, very small. As a result, it doesn't make much sense to count them individually when doing a chemical reaction. As a result, scientists have come up with a shorthand term for a very large number of molecules, just as shoe salesmen have a term for two shoes, grocers have a term for 12 eggs, and paper salesmen have a term for 500 sheets of paper. That term is mole, and it stands for 6.022136736 × 1023 things (we'll usually just round it to 6.02 × 1023).


6.02 × 1023 is usually referred to as Avogadro's number and is named after the chemist Amadeo Avogadro, who helped to understand the nature of gases.

In our everyday lives, moles aren't a particularly handy unit for measuring numbers of things. For example, let's say that the publisher of a book decided to print a mole of copies for sale worldwide. Such a number of books would require a warehouse with a volume of 512 billion cubic kilometers. Unfortunately, my agent wasn't able to convince the publisher that this would be a good business move. As a result, we should only use "moles" to describe numbers of really small things like atoms or molecules.

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Excerpted from The Complete Idiot's Guide to Chemistry © 2003 by Ian Guch. All rights reserved including the right of reproduction in whole or in part in any form. Used by arrangement with Alpha Books, a member of Penguin Group (USA) Inc.

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