1. Chemical Composition … Moles Chemistry Mr. Lentz

2. Standards Addressed 3.1.10 D Apply scale as a way of relating concepts and ideas to one another by some measure. 3.4.10 A Explain concepts about the structure and properties of matter.

3. Unit Topics 1. Atomic mass 2. Mole definitions 3. Percent composition 4. Empirical formulas 5. Molecular formulas

4. Some Definitions Atomic particles: Atomic number: Mass number: Isotopes: Atomic mass: –Mass spectrometer …

5. Atomic Mass May be better described as an average atomic mass … Carbon has two common isotopes … C-12 … 99.89% (.9989)(12) = 11.8668 C-13 … 1.11% (.0111)(13) = 0.1443 12.011 12.011

6. Atomic Mass Actual masses of elements … –Hydrogen = 1.66 X 10 -24 g –Carbon = 1.99 X 10 -23 g –Oxygen = 2.66 X 10 -23 g Atomic Mass Scale (amu) –Hydrogen = 1.0 amu –Carbon = 12.0 amu –Oxygen = 16.0 amu

7. Problem There is no easy way to measure the mass of one atom Solution … –Change amu to grams –Determine how many atoms are in 12.011 g of Carbon –Give this number a name

8. Avogadro’s Number Is the number of atoms in 12.011 g of carbon Is equal to 6.02 X 10 23 OR602,000,000,000,000,000,000,000.

9. The Mole Scientists gave Avogadro’s number of things a name … a MOLE

10. One Mole 1 mole of marbles would cover the earth 50 miles deep 1 mole of grains of sand would cover the US 1 cm deep Could you count to Avogadro’s number?

11. Moles Defined 1 mole = 6.022 X 10 23 “things” 1 mole = mass in grams (usually called molar mass)

12. Molar Mass Units … grams / mole For elements … it is the atomic mass in grams For compounds … it is the sum of the masses of the elements present

13. Molar Mass What is the molar mass of copper? answer = 63.6 g What is the molar mass of water? H 2 O H (2)(1.0) = 2.0 O (1)(16.0) = 16.0 O (1)(16.0) = 16.0 18.0 g/mole 18.0 g/mole