Units of Counting Dozen Pair Gross Ream

122

144500

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

Counting M&M’s

• What other conversion factor do we need? – Remember we have these

• 1 bag = 1190.7g• 1 M&M = 0.85g

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 Pair Gross Ream Party-sized Bag Moles (abbreviated: mol)

122

144500

1400 M&Ms6.022 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 12.0000g 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