Topic Counting Atoms and Formula Mass the MOLE

Topic: Counting Atoms and Formula Mass (the MOLE) Do Now: complete package page 2 Here is an example Na. Cl = 1 Na atom , 1 Cl atom H 2 SO 4 = 2 H atoms , 1 S atom , 4 O atoms

Lets starting my counting atoms in a single molecule • Na. Cl Na = 1 Cl = 1 total atoms = 2 • H 2 SO 4 H = 2 S = 1 O = 4 total atoms = 7 • Cu(NO 3)2 Cu = 1 N = 2 O = 6 total atoms = 9 What happens if there is a coefficient in the front? = More then 1 molecule • 5 Na. Cl Na = 5 Cl = 5 total atoms = 10 – 5 molecules of Na. Cl • 2 Cu(NO 3)2 Cu = 2 N = 4 O = 12 total atoms = 18

We can count the number of atoms in one molecule of water (H 20). 2 Hydrogens 1 Oxygen But in a 100 ml of water, how many H atoms / O atoms are there? Thousands, Millions, Billions? THINK BIGGER MUCH BIGGER MOLE VIDEO LINK

Thanks to Avogadro, we can calculate that there are … • 6, 680, 000, 000, 000 • (6. 68 x 1024) Hydrogen atoms in 100 ml (less then a ½ cup) of water

1 Mole = 6. 02 x 1023 particles = Avogadro's # • Used to “count” numbers of atoms • Defined as # of atoms in 12 g of C-12 – This is the standard 6. 02 x 1023 atoms – So, 12 g of C-12 has ______ • This is a really big number – It’s so big because atoms are really small! – HOW SMALL? ! (link) No, not this kind of mole!

• One mole of water = 6. 02 X 1023 water molecules • One mole of gorillas = 6. 02 X 1023 gorillas • One mole of He atoms = 6. 02 X 1023 He atoms • One mole of anything = 6. 02 X 1023 of that thing

Equalities • 1 mole of C-12 • 0. 5 mole of C-12 = = • 12. 0 grams of C-12 • 6. 0 grams of C-12 = = • 6. 02 X 1023 atoms of • 3. 01 X 1023 atoms of C-12

Remember how to find Atomic Mass? 9. 0122 amu = 9 amu

• Formula mass (Gram Formula Mass –GFM) take atomic mass of any element and replace amu with grams – 9. 0122 amu = 9. 0122 g • So, in 9 g of Be there are 6. 02 X 1023 atoms or 1 mole

– Molar mass = formula mass per mol (g/mol) 1 mole of H weighs 1. 0079 g 6. 02 x 1023 H atoms 1. 0079 g/mol 1 mole of C weighs 12. 011 g 6. 02 x 1023 C atoms 12. 011 g/mol 1 mole of U weighs 238. 029 g 6. 02 x 1023 U atoms 238. 029 g/mol • Chemists use this to convert between the number of atoms to an actual mass that they can measure in the lab

Calculating Formula Mass (GFM) 1. 2. 3. 4. COUNT Atoms LOOK UP Atomic Mass ( and round) Multiply by number of atoms Add • CH 2 Cl 2 – C = 1 X 12 = 12 –H=2 X 1 =2 – Cl = 2 X 35 = 70 84 g Molar Mass = 84 g/mol