2. Units of Counting  Dozen  Pair  Gross  Ream 12 2 144 500

4. Counting M&M’s Example 1:How many M&M’s are in one party-sized bag? – Given on the bag… 1 bag = 1190.7g – We want… # M&M’s per bag

5. Counting M&M’s What other conversion factor do we need? – Remember we have these 1 bag = 1190.7g 1 M&M = 0.85g

6. Counting M&M’s We can even go backwards! – Example 2: We have 3.96 x 10 9 M&M’s. How many bags of M&M’s do we have when we’ve got 3.96 x 10 9 M&M’s? Keep your answer in scientific notation. Round to the nearest hundredth

7. Counting M&M’s We can go one step farther with this! – Example 3: We have 3.96 x 10 9 M&M’s. How many grams of M&M’s do we have when we’ve got 3.96 x 10 9 M&M’s? Keep your answer in scientific notation. Round to the nearest hundredth

8. Counting M&M’s as an analogy We counted 1400 M&M’s without physically counting them. – We counted M&M’s by mass. That is what chemists do with the number of particles in chemicals. – Chemists count particles by mass.

9. Units of Counting  Dozen  Pair  Gross  Ream  Party-sized Bag  Moles (abbreviated: mol) 12 2 144 500 1400 M&Ms 6.022 x 10 23 particles Simply a counting unit

10. Avogadro’s Number Named after Italian scientist Avogadro DID NOT discover Avogadro’s number – His work paved the way to the discovery His work inspired other scientists to experiment on pure carbon-12 – They found that there are 6.0221367 x 10 23 atoms in exactly 12.0000g of pure carbon-12

11. Avogadro’s Number Definition: the number of particles in a mole. This number is 6.022 x 10 23 – Written as 6.022 x 10 23 particles/mol In the M&M analogy: 1400 M&Ms/bag

12. Molar Mass The mass of one mole Units are g/mol In the M&M analogy g/bag Round the atomic mass from the periodic table to the second decimal place