EES 4200 Worksheet 4, 2/4/02-2/11/02
TOPICS: Isomers, Resonance, Molecular Shapes, VSEPR Theory, Molecular Orbitals
1. Isomerization describes when more than one molecule shares the same molecular
formula. There are two major types of isomers: constitutional and stereo-isomers.
Constitutional isomers may be skeletal, functional group or positional in type. Identify
the following sets of compounds as one of the types of constitutional isomers.
and Skeletal and Functional group
and OH Positional
2. Rank single, double, and triple bonds in the order of bond lengths. Bond strengths.
Strength: triple> double>single
[Be able to explain these trends!]
3. Why are the N-O and N=O bonds in CH3NO2 shown to be of equal length? Due to
resonance. The real structure is a hybrid of these 2 resonance structures. Draw the
resonance structures for this compound.
H3C N H3C N
4. Electrons in a Lewis structure are said to be stable, whereas electrons in a resonance
structure are said to be delocalized. A structure that has delocalization of electrons tends
to be MORE or LESS (circle one) stable than those without delocalization. Give an
example of a compound that has delocalized electrons and is considered unreactive in the
environment. Example: Benzene
5. The Valence Shell Electron Pair Repulsion Model states that electron pairs of atoms are
as far away as possible. As a result, the basic structure of an atom with two electron
pairs in the valence shell is linear; with three electron pairs, trigonal, with 4 pairs,
6. Specify the geometry of the following compounds:
a. H-C=N: (hydrogen cyanide) b. H4N+ (ammonium ion)
7. Does carbon dioxide, O=C=O, contain polar bonds? Yes, it has 2 double bond C-O polar
bonds. Is the carbon dioxide molecule polar? No, because forces cancel each other. Why
or why not?
8. Are the following compound polar?
a. water, H2O b. formaldehyde, H2C=O c. methane, CH4
YES YES NO
9. A dipole results when a bond is formed between two atoms that have a large difference in
electronegativity. The magnitude of the polarity of a bond is known as its dipole
moment. The polarity is the measure of a molecule’s electron density imbalance.
10. Name the three types of hybridization that can exist with carbon atoms bonding with
other atoms: sp3, sp2, and sp. These correspond to single, double, and triple bonds.
11. The strongest (least reactive) of the bond types are triple bonds. Explain this in terms of
molecular orbital theory.