1. 1 Chapter 9 Orbitals and Covalent Bonds

2. 2 Two types of Bonds l Sigma (  ) bonds from overlap of orbitals l They are between the atoms Pi bond (  bond) above and below atoms and l Between adjacent p orbitals. A  bond makes the first and a  bond makes the second bond of a double bond

3. 3 Localized e- model: Summary n Draw the Lewis structure(s) (resonance) n Determine arrangement of e - pairs using the VSEPR model. n Specify hybrid molecular orbitals need to accommodate the e - pairs. n Do the steps in this order! n http://www.bluffton.edu/~bergerd/classes/CEM222/Handouts/spanimati on.html http://www.bluffton.edu/~bergerd/classes/CEM222/Handouts/spanimati on.html http://www.bluffton.edu/~bergerd/classes/CEM222/Handouts/spanimati on.html

4. 4 Summary of sigma & pi bonds Single bond - composed of one  comprised of overlapping orbitals  Single bond - composed of one  comprised of overlapping orbitals  Double bond - composed of one  and one  is between p orbitals)  Double bond - composed of one  and one  is between p orbitals)  Triple bond - composed of one  and two  bonds. Triple bond - composed of one  and two  bonds. n Know this for the online homework!

5. 5 Molecular Orbital Summary n 1. Molecular orbitals are either bonding or antibonding; n 2. Bonding orbitals are lower in energy than corresponding atomic orbitals while antibonding orbitals are higher; n 3. MO theory helps explain paramagnetism & diamagnetism; n 4. MO theory obviates "resonance", replacing it with delocalized pi bonding. http://www.wwnorton.com/chemistry/tutorial s/ch6.htm http://www.wwnorton.com/chemistry/tutorial s/ch6.htm

6. 6 Magnetism n Magnetism has to do with electrons. n Paramagnetism attracted by a magnet. n Associated with unpaired electrons. n Diamagnetism repelled by a magnet. n Associated with paired electrons. n B 2 is diamagnetic.

7. 7 Bond Order n The difference between the number of bonding electrons and the number of antibonding electrons divided by two.

8. 8 Bond Order n The difference between the number of bonding electrons and the number of antibonding electrons divided by two. n E.g., H 2 has 2 bonding electrons (the covalent bond) and 0 antibonding (no other electrons). n B.O. = (2 - 0) ÷ 2 = 1 n H 2 1- ion has 2 bonding + 1 antibonding n B.O. = (2 - 1) ÷ 2 = 1/2 n The non-ion is more stable because it has the higher bond order.

9. 9 Bond Order n Use bond order to explain why He is monoatamic vs. diatomic. n He bond order = (2 - 0) ÷ 2 = 1 n He 2 has 2 bonding and 2 anti-bonding n (2 - 2) ÷ 2 = 0 n So He is monoatomic is more stable because it has the higher bond order. n End of our part of 9.2