Units of Counting

2. Units of Counting 12 • Dozen • Pair • Gross • Ream 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 109 M&M’s. How many bags of M&M’s do we have when we’ve got 3.96 x 109 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 109 M&M’s. How many grams of M&M’s do we have when we’ve got 3.96 x 109 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 12 • Dozen • Pair • Gross • Ream • Party-sized Bag • Moles (abbreviated: mol) 2 144 500 1400 M&Ms 6.022 x 1023 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 1023 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 1023 • Written as 6.022 x 1023 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