Molecular Shapes; The Vsepr Theory Worksheet

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Molecular Shapes; The Vsepr Theory Worksheet Powered By Docstoc
					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.
                                                       OH         O
             and           Skeletal                         and                   Functional group

                     and    OH            Positional

2. Rank single, double, and triple bonds in the order of bond lengths. Bond strengths.
                Length: triple<double<single
                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.
           O                       O
         +                            +
H3C    N                   H3C        N
             O                              O

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)
       Linear                                      Tetrahedral
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.

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