oh yay, finally a chance to use what little i remember from my years as a chem major:

You're right about a mole being a measure of atoms; it's actually the amount in grams of a particular substance required in order for the sample to have as many atoms (or basic elements, including ions) as .012kg of the standard C-12 atom (a mole of C-12 weighs 12 grams), which Avogadro discovered is about 6.02 times 10 to the 23rd power. therefore 1 mol = number of atoms in 12g of C-12 atoms = 6.02 x 10 to the 23rd atoms. this grammatical mass constitutes the substance's molecular weight (there's your entymology, helen), which is quite similar to the atomic weights which Mendeleyev used (though in a couple of cases not exactly) to formulate his Periodic Classification of the elements.