Lets say you have 2.5 moles of Au (Gold) and you’re really curious as to how many atoms of gold are in that sample. What should we do? Well just remember what Chemistry Cat says about MOLE PROBLEMS:

For any element or compound, 1 mole is equal to Avogadro’s Number of particles of that element or compound.

1 mole = 6.022 x 10²³

So, lets start plugging into a factor label equation the same way we did for Moles to Grams equations.

2.5 mole Au atoms   ->   __________  Au atoms

Since 1 mole is equal to Avogadro’s number, we can put that into our formula as…

6.022 x 10²³ Au atoms
1 mole Au atoms

So lets put this value into our formula and see if we can make this work…

2.5 mole Au atoms   x   6.022 x 10²³ Au atoms
1                                      1 mole Au atoms

We can cross out the “mole Au atoms” units so the only unit remaining is “Au atoms“. So…

2.5 x 6.022 x 10²³ Au atoms       =       1.506 x 10²⁴ Au atoms

___________Easy! When you go from grams to moles you MULTIPLY BY THE ATOMS!_______________
But, what if I want to go from atoms to moles??? EASY!!! DIVIDE BY AVOGADRO’S NUMBER!
How many moles of Zn is 2.75 x 10²⁴ atoms of Zn?

2.75 x 10²⁴ Zn atoms   x   1 mole Zn atoms            =  4.57 mole Zn atoms
1                                      6.022 x 10²³ Zn atoms

Since, 1 mole of any element = Avogadro’s number of atoms (or molecules), you can flip the equation to work for you! Since we have moles on the top left of the formula, we want moles on the bottom right so they can cancel out!

Your homework for tonight is to finish the second 10 problems (the back side) of the  Moles Conversions Worksheet (found on semester 1 Docs). You can also watch the Voicethread on mole conversions using the App or the semester 1 Notes Page.