Units of Counting Dozen 12 Pair 2 Gross

Units of Counting § § Dozen 12 Pair 2 Gross 144 Ream 500

Counting M&M’s • Example 1: How many M&M’s are in one party-sized bag? – Given on the bag… • 1 bag = 1190. 7 g – We want… • # M&M’s per bag

Counting M&M’s • What other conversion factor do we need? – Remember we have these • 1 bag = 1190. 7 g • 1 M&M = 0. 85 g

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

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

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.

Units of Counting § § § Dozen 12 Pair 2 Gross 144 Ream 500 Party-sized Bag 1400 M&Ms Moles (abbreviated: mol) 6. 022 x 1023 particles Simply a counting unit

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. 0000 g of pure carbon-12

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

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