2. Seek First to Understand… Q : Why is knowing about Molecular geometry important?

3. Linear = odorless  nontoxic Bent = strong “rotten eggs” odor Toxic levels  1 dropperful in railroad car filled with water Human detection level 0.47 ppb  1/10 th of one drop in a railroad car of water (10 million receptors) (sweet, salty, sour, bitter) CO 2 H2SH2S

4. 1 234567 8 # Valence electrons X X X X X X X X

5. Lewis Dot Structures: Electron dot structures of compounds Q: What is the formula for water? H2OH2O Q: How many valence electrons does each hydrogen have?1 Q: How many valence electrons does the oxygen have?6 Q: How many valence electrons are there in each water molecule? #VE = 2H + 1 oxygen =2(1) + 6 = 8 More examples 1. How many VE in H 2 O 2 ? #VE = 2(1) + 2(6) = 14 H O 2. How many VE in H 2 SO 4 ? #VE = 2(1) + 6 + 4(6) = 32 HSO

6. The ‘Keep ‘em Happy’ approach to Lewis structures: 1. Convert name  formula and add up total# valence electrons 2. Draw the stick-skeleton of the molecule (central atom is underlined) 3. Add electron pairs so each atom has 8 around it Exceptions: H only needs 2e- and B only needs 6e- BF3BF3 BF F F VE = 3 + 3(7) = BF (each stick = 2 electrons) 24 4. Check electron count OF2OF2 VE = 6 + 2(7) = O F 20OF F Examples Boron trifluoride Oxygen difluoride

7. 1.Build 3D models of the molecules from your “From Dots to Jelly Beans” lab sheet using toothpicks and jelly beans. The jelly beans are the atoms A full tooth pick is a covalent bond between atoms A half-toothpick shows the position of lone pairs (the PAIRS of dots) For example, would be H—H, while is H—F 2. Look at the balloon models for the MOLECULAR GEOMETRY, and make ADJUSTMENTS to the geometry of your models necessary. 3. LABEL your model with the COMPOUND FORMULA using a piece of masking tape H2H2 HF