2. The Mole Unit 3

3. The Mole So far we have been dealing with numbers on the atomic scale… –Atomic Number = # of protons –Mass Number = # of protons + # of neutrons –Atomic Mass = # of amu in one average atom

4. The Mole This is a really small scale. Is it logical to try to measure out chemicals for labs this way? NO! We need a bigger scale to use for everyday measurements and calculations.

5. The Mole We need… The MOLE! The MOLE is a unit of measure – a unit of “how many”.

6. The Mole Just like a dozen eggs tells us “how many” eggs, a mole tells us “how many” particles. 1 dozen eggs = 12 eggs 1 mole = 6.02 x 10 23 particles –Particles can be anything – atoms, molecules, eggs, etc.

7. The Mole This number (6.02 x 10 23 ) is called Avogadro’s Number, in honor of Amedeo Avogadro’s contributions to chemistry. Unfortunately for him, his ideas weren’t really recognized as important until after he died.

8. The Mole But wait, where did we get this number? Scientists have found that there is exactly 1 mole of atoms in the atomic mass of an element when that mass is expressed in grams. Huh?

9. For example: What is the atomic mass of C-12? (Hint – there is only one isotope here, so think mass number) Atomic mass = 12 amu

10. The Mole Then express that mass in grams  12 g In exactly 12 grams of C-12, there is one mole (6.02 x 10 23 ) of atoms. This also works for our average atomic masses (from the periodic table).

11. The Mole So, in exactly 12.01 g of natural carbon there are 6.02 x 10 23 atoms. AND, 6.02 x 10 23 atoms = 1 mole. So 1 mole of carbon = 12.01 g. Hmm…..those sounds suspiciously like conversion factors… Time for examples!

12. The Mole How many atoms are in 1.00 mole of gold? 1.00 mole Au 6.02 x 10 23 atoms 1 mole = 6.02 x 10 23 Atoms Au

13. The Mole How many molecules are in 2.00 moles of water? 2.00 mole H 2 O 6.02 x 10 23 molecules 1 mole = 1.20 x 10 24 Molecules H 2 O

14. The Mole How many marbles are in 1.00 mole of marbles? (Enough to cover the entire Earth to a depth of 50 miles!) 1.00 mole marbles 6.02 x 10 23 marbles 1 mole = 6.02 x 10 23 marbles

15. The Mole How many grams are in 1.00 mole of neon? 1.00 mole Ne 6.02 x 10 23 atoms 1 mole Ne =20.2 g Ne 6.02 x 10 23 atoms 20.18 g Ne