Chapter 8 Homework posted Lab Notes Today’s Topic: Bond Properties (Sec there is no 8.3!) Electron Distribution in Molecules (8.5) November 16, 2009

Rules for Drawing Lewis Structures 1. Write the skeletal structure 2. Add up the total # of valence electrons 3. Draw a bond between the central atom and each surrounding atom 4. Add lone pairs to the outer atoms to complete their octets 5. Add remaining electrons to central atom 6. If central atom does not have an octet, “borrow” electrons from other atoms (make double/triple bonds)- DO NOT ADD ELECTRONS (F and Cl do not form multiple bonds; C, N, O, P, and S do) 7. Sometimes you can’t complete an octet (B and Be)

Did you try this at home? Here’s the answer… __# electrons__ C = 4 H = 2 x 1 = 2 Cl = 2 x 7 = 14 Total = 20

Organic Structures CHCCHCH 2

What can we do with Lewis Structures? Bond Properties 1. Polarity 2. Bond Order 3. Bond Length 4. Bond Energy

Bond Types Nonpolar Covalent Polar Covalent Ionic Imagine they are nuclei Imagine this is a valence electron

Polarity Electronegativity- The ability of an atom involved in a bond to attract electrons to itself  Orbital energy, effective nuclear charge

Polarity Electrons drawn closer to the more electronegative atom

Trend in Electronegativities

Bond Character: From Covalent to Ionic

In a C-O bond, which element will have a greater concentration of electron density? 1. Carbon 2. Oxygen 3. Neither, they will share the electrons equally

Bond Order The number of bonding electron pairs between two atoms

Bond Length Atom size Bond order

Which bond is the longest? 1. H - H 2. H - Cl 3. Cl - Cl 4. Cl - Br 5. Br - Br

Which bond is the shortest? 1. N-N 2. N=N 3. N  N 4. All are the same length