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.

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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