1. A New Unit of Measurement A Chemistry Exclusive!!

2. Dude!!!! Atoms are REALLY small!!!!!! We can’t work with individual atoms or amu’s in the LAB –Because we can’t see things that small.

3. We work with samples large enough for us to SEE and WEIGH on a balance using units of grams.

4. This creates a problem….. A pile of atoms big enough for us to see contains billions of atoms. –Billions of atoms are hard to keep track of in calculations.

5. So chemists made up new unit..

6. What’s a MOLE? It is a number of things –Just like a “dozen” –1dozen eggs= 12 eggs –1 mole eggs = 6.022 x 10 23

7. POP QUIZ 1 dozen Mg atoms = 12 Mg atoms 1 mole Mg atoms = 6.022 x 10 23 atoms 1 mole Mg(OH) 2 = 6.022 x 10 23 molecules 1 mole O 2 = 6.022 x 10 23 molecules

8. Everybody Dance Now!!! “Moleshake” My moleshake brings all the moles to the yard, And they’re like, “Man, Chemistry’s hard” Yeah right, yeah Chemistry’s hard, I can teach you, and I won’t even charge

9. How Big is a Mole? A mole of marbles would cover the entire Earth’s surface 50 MILES DEEP!!!

10. How Big is a Mole? If you spent a BILLION DOLLARS every second, you couldn’t spend a mole of dollar bills in your lifetime!!!

11. Avogadro’s Number 6.022 x 10 23 is referred to as Avogadro’s Number - In honor of Amedeo Avogadro, Italian chemist (1776-1865) Ladies….. You know you want me.

12. ….and if Avogadro rings, ask him to leave his number…”

13. A “new” look at the periodic table… We already know the periodic table tells us the mass (in a.m.u.’s) of a single atom –Ex. 1 Al atom has a mass of…. 26.9 grams Ex. 1 mole of Mg atoms has a mass of… 24.31 grams/mol

14. So MASS on the periodic table has two meanings… 1. When interpreted as grams/mole (g/mol) we call it “molar mass” 2. When interpreted as amu’s (g) we call it “atomic mass” The number doesn’t change, only the units.

15. This also applies to molecules The molecular mass of NH 3 is… –The mass of 1 individual NH 3 molecule 14.01 amu + 1.01 17.04 amu (g) of NH 3 Or… 17.04 g/mol of NH3 if you are interpreting for molar mass.

16. Practice Problems 1. What is the atomic mass of Carbon? –12.01 g or amu 2. What is the molar mass of Carbon? –12.01 g/mol What is the molar mass of Mg 3 (PO 4 ) 2 ? –262.87 g/mol How many moles of Oxygen are in 1 mole of Mg 3 (PO 4 ) 2 ? –8 moles of Oxygen