Units of Counting  Dozen  Pair  Gross  Ream

Counting M&M’s Example 1:How many M&M’s are in one party-sized bag? – Given on the bag… 1 bag = 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 = g 1 M&M = 0.85g

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

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

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) M&Ms x 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 x atoms in exactly g of pure carbon-12

Avogadro’s Number Definition: the number of particles in a mole. This number is x – Written as x 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