1. EXAM #3 Correction- Check OWL Chapter 8 Homework posted Today’s Topic: Lewis Structures (Sec. 8.2) Bond Properties (Sec. 8.3) November 11, 2009

2. Why does a covalent bond form? 1. The valence electrons on two atoms are attracted to one another 2. The nuclei of two atoms are attracted to one another 3. The valence electrons on one atom are attracted to the nucleus of another atom 4. The repulsive forces between the protons in two nuclei and between the electrons in two atoms are strong

3. Last time… Bonds form when the balance of forces favors bond formation Valence electrons are those in the outermost shell (highest n-level) Lewis structures are used to show the valence electrons  Elemental symbol = core (nucleus + inner electrons)  Lines = bonding electrons  Dots = electrons not involved in a bond

4. 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)

5. How many total bonding electrons does an acetate ion have? 1. 7 2. 8 3. 10 4. 12 5. 13 6. 14 7. 15

6. Examples Try this one at home!

7. Draw the Lewis structure for SO 3. How many lone pairs does it have? 1. 2 2. 4 3. 6 4. 8 5. 10

8. What does the Lewis Structure for N 2 look like? 1. 2. 3. 4.

9. Exceptions to the Octet Rule H (2) Be (4) B (6) Large elements with available d orbital

10. Organic Structures CH 3 CH 3 CH 3 CN CHCCHCH 2