CHEM 1A03 LECTURE 6 – CHEMICAL BONDING CONTINUED
October 2 2012
**Ch 8,9,10 and Fundamental Skills Review is the content on the midterm.
7:00PM In BSB 147
Lewis Dot Diagrams : [BrOF ] 2
1. Count valence electrons
i. 7 e- from bromine, 14 from flourines, 6 from O, take away 1 for the
ii. 26 e- available.
2. Make the distinct atom with most electrons the terminal (central) atom.
3. Put other elements around it and connect w/ single bonds
4. Add electrons to fill all octets
5. Calculate formal charge.
a. Br = 7-3-2 = +2
b. O = 6-1-6 = -1
c. F = 7-1-6 = 0
6. To minimize charges, add a double bond between O and Br
a. Br = 7e- – 4bonds – 2(nonbonding)e- = +1
b. O = 6e- - 2bonds – 4(nonbonding)e- = -2
• Octet is not exceeded in Period 2
o C N O F cannot over fill
o cannot exceed the “octet rule” even if there are adjacent formal charges that
could be minimized
• For elements in Periods 3, 4, etc., minimizing formals charges is the priority, even if it
means breaking the “octet rule”
o Usually don’t have adjacent atoms with same formal charge. o Negative formal charges usually appear on the most electronegative atoms,
positive charges on the most electropositive atoms
o O2 molecule binds to iron of the heme unit.
o Geometry around iron changes as O2 is bound vs. free
o Carboxyhemoglobin: CO binds competetively to the heme unit and displaces O 2.>200
ppm = dizziness + convulsions
o Saturation with oxygen can reverse the process. The binding is an equilibrium process.