Typical Bonding in Organic Chemistry
Major concepts
 Valence is a quick and easy way to recognize and predict typical bonding patterns
 Lewis Dot structures are a formalism to help us communicate basic molecular structure in terms
of valence electrons
 The octet rule and formal charge dictate typical bonding patterns
 Constitutional isomers have the same molecular formula, but different bonding
Vocabulary
 Valence
 Constitutional isomer
 Hydrocarbon
 Cyclic and acyclic compounds
 Lewis Dot structure
 Covalent bond
 Lone pair
 Octet rule
 Formal charge
Students should be able to:
 Recognize typical and atypical bonding in a given structure
 Draw typically bonded molecules given a molecular formula
 Recognize constitutional isomers
 Draw a set of constitutional isomers for saturated compounds
Daily problems
1. Construct your own periodic table of the 10 most important elements for organic chemistry.
A. What are the 4 most common elements we will work with? C, N, O, H
B. What element has the same valence as nitrogen? P
C. What element is to the right of oxygen on the periodic table? F Which is below oxygen S
2. Use valence model to draw a structure for
A. An acyclic hydrocarbon with six carbon atoms
B. A cyclic hydrocarbon with five carbon atoms
3. According to the valence approach of bonding, which of these structures is/are an acceptable
bonding pattern for C2H6O? If a structure is wrong, explain how you know it is unacceptable.
1. Unacceptable: C1 does not have a complete octet, and the Oxygen atom has 1 too many bonds.
2. Acceptable
3. Unacceptable: C1 does not have a complete octet, and the Hydrogen and Oxygen (adjacent to
each other) both have 1 too many bonds
4. Acceptable
4. Given these molecular skeletons, fill in the structures with bonds to hydrogen atoms, and lone pairs,
assuming typical bonding.
5. Which of the atoms in these molecules does not have a zero formal charge?
6. Draw Lewis structures for all typically bonded constitutional isomers of
a. C4H10
b. C4H9F
are not the
c. C4H10O
Extension Problems
7. In the hydrocarbons we have discussed so far, if a molecule has 4 carbon atoms, it has 10 hydrogen
atoms. If it has five carbon atoms, it has 12 hydrogen atoms. If it has six carbons, it has 14 hydrogen
atoms. The general pattern emerges that these are CnH2n+2 compounds, where n is the number of
carbon atoms. Draw a number of acyclic hydrocarbon compounds with six carbon atoms, and see if you
can see the pattern of why there are never more or less than 14 hydrogen atoms. Think about the
physical basis of the CnH2n+2 rule.
8. Based on what you learned above, how many hydrogen atoms would be in an acyclic hydrocarbon
with seven carbons? 16 With 53 carbons? 108
9. We have mainly discussed acyclic compounds, but carbon atoms can also bond in such a way that a
cycle is formed (see problem 2 above.) Draw as many cyclic hydrocarbon compounds with 5 carbon
atoms as you can. (At this point, you should be able to draw 5 distinct ones.)
10. Cyclic compounds, like those in problem 9, do not follow the CnH2n+2 rule. What rule do they follow?
CnH2n