1. Unit 4 The Mole and Molar Mass

2. Read pages 55-57 HW: WS: Lewis Dot and Naming Acids Mole Worksheet: Number 2, #1-3 Quiz: Thursday or Friday Feb. 7 th or 8 th Lesson 1 Unit 4

3. MEASURING MATTER 3 ways to measure things: count: 1 dozen = 12 apples mass: 1 dozen = 2 kg of apples volume: 1 dozen = 0.20 bushel (for typical wicker basket)

4. MASS OF A SINGLE ATOM To calculate the mass of ONE atom of carbon: 1 amu = one proton or one neutron = 1.66 x 10 -24 g mass of one C atom = 1.995 x 10 -23 g IMPOSSIBLE, IMPRACTICLE!

5. MASS OF MANY ATOMS One atom cannot be weighed. Can we weigh many atoms and still determine relative masses of different atoms? …

6. HELIUM ATOM VS. NITROGEN ATOM 1400 amu400 amu100 atoms 140 amu40 amu10 atoms 28 amu8 amu2 atoms N = 14 amuHe = 4 amu1 atom Mass ratio ( 2 : 7 ) is always the same!

7. AVOGADRO’S NUMBER number of atoms whose mass in grams = mass of one atom in amu example: carbon 1 carbon atom = 12.01 amu ?? atoms = 12.01 grams of carbon ANSWER: 6.02 x 10 23 atoms!

8. We call this number of “things” one MOLE: 6.02 x 10 23 “things” = 1 mole just like 12 “things” = 1 dozen AVOGADRO’S NUMBER

9. “THINGS”: REPRESENTATIVE PARTICLES 1 mole = 6.02 x 10 23 representative particles 1 mole carbon = 6.02x10 23 atoms 1 mole CO 2 = 6.02x10 23 molecules 1 mole NaCl = 6.02x10 23 formula units

10. 1 atom of hydrogen = 1.01 amu 6.02x10 23 atoms of H = 1.01 grams 1 mole of H = 1.01 grams usually written as: 1.01 g/mole This number is called the MOLAR MASS of hydrogen. THE MOLE AND MOLAR MASS

11. MOLAR MASS carbon: MM = 12.01 g/mole 12.01 g = 1 mole = 6.02x10 23 atoms magnesium: MM = 24.34 g/mole 24.34 g = 1 mole = 6.02x10 23 atoms 1 mole = same number of atoms = different number of grams

12. MOLAR MASS What is the molar mass of sulfur? 32.07 g/mole What is the molar mass of SO 3 ? 80.07 g/mole What is the molar mass of NaCl? 58.44 g/mole

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