Opener:

1. Opener: How many eggs are in a dozen? People are in a couple? Pencils are in a gross? Does the number of things change if the objects do?

2. Answers to homework: #1 8.46x109 + 1.23x1011 = 8.46x109 + 123.x109 = 131.46x109 = 1.3146x1011 or .0846x1011 + 1.23x1011= 1.3146x1011

3. #2 9.84x1014- 6.18x1015 = 0.984x1015 - 6.18x1015 = -5.196x1015 or 9.84x1014 - 61.8x1014= -51.96x1014 = -5.196x1015

4. #3 (2.91x106)(4.33x104) = (2.91 x 4.33) x10(6+4) = 12.6x1010 = 1.26 x 1011

5. #4 7.94x1010∕ 3.24x103 = (7.94/3.24) x10(10-3)= 2.45x107

6. 1 dozen = ? • A couple = ? • A gross = ? • A mole = ?

7. 1 dozen = 12 • A couple = 2 • A gross = 144 • A mole = 6.022x1023

8. Why do we care? • 6.022 x 1023 is Avagadro’s number. He discovered that the atomic mass of an element, in grams, has exactly 6.022 x 1023 atoms.

9. SO, 1 Carbon atom weighs 12 amu • but 1 moleof carbon atoms weighs 12 grams • which means 6.022x1023 atoms of carbon weighs 12 g

10. So….we can convert between grams, moles, and # of particles! • (particles can be atoms, molecules, or ions) • Here’s how…

11. mw= molecular weight (for atoms this is the atomic mass on the periodic table…..for molecules you’ll add all the atomic masses together)

12. Let’s try some… • How many moles of nitrogen atoms are in a 36g sample?

13. How many moles of nitrogen atoms are in a 36g sample? 36 g N ÷ 14 g/mol = 2.57 mol

14. How many grams of sodium atoms are in a 6 mole sample?

15. How many grams of sodium atoms are in a 6 mole sample? 6 moles x 23 g/mol = 138 g

16. How many atoms are on a 9 mole sample of donuts?

17. How many atoms are on a 9 mole sample of donuts? • 9 moles x 6.022 x 1023= 5.42 x 1024

18. 9.45x1028 atoms are equal to how many moles?

19. 9.45x1028 atoms are equal to how many moles? 9.45x1028atoms ÷ 6.022 x 1023atoms/mole = (9.45 ÷ 6.022) x 10 (28-23) = 1.57x10 5

20. Closer • describe the term "mole"? How is it like the term "dozen"? • Homework: Do pg 102 # 1-4 and pg 103 1-3.