AP Chemistry
Worksheet : Obj 17-26-3
Name :
Date :
1. Acetic acid is responsible for the sour taste of vinegar. It can be manufactured using the following
reaction:
Use tabulated values of bond energies (Table 8.4) to estimate ΔH this reaction.
2. The standard enthalpies of formation for S(g), F(g), SF4(g), and SF6(g) are +278.8, +79.0, -775,
and -1209 kJ/mol, respectively.
a. Use these data to estimate the energy of an S—F bond.
b. Compare your calculated values to the value given in Table 8.4. What conclusions can you
draw about where the value for the S-F bond comes from?
c. Why are the ΔHf° values for S(g) and F(g) not equal to zero, since sulfur and fluorine are
elements?
B. Lewis Structures and Resonance
3. Write Lewis structures that obey the octet rule for each of the following. (First element is central
unless noted otherwise)
a. HCN (C is central)
c. CHC13(C is central)
b. PH3
d. NH4+
4. Write Lewis structures for the following molecules or ions, which have central atoms that do not
obey the octet rule:
a. PF5
c. BH3
d. Br3b BeH2
Ch. 8 and 9 : Ws – obj 17-26-3
5. Write Lewis structures for the following. Show all resonance structures where applicable.
a. NO2-
b. OCN- (C is central)
c. N3-
6. Benzene (C6H6), consists of a six-membered ring of carbon atoms with one hydrogen bonded to
each carbon. Write Lewis structures for benzene, including resonance structures.
7. An important observation supporting the need for resonance in the localized electron model was
that there are only three different structures of dichlorobenzene (C6H4Cl2). How does this fact
support the need for the concept of resonance.
8. Order the following species with respect to carbon-oxygen bond length (longest to shortest).
CO,
CO2,
CO32- CH3OH
Formal Charge
9. Use the formal charge arguments to rationalize why BF3 would not follow the octet rule.
10. When molten sufur reacts with chlorine gas it produces a foul smelling orange liquid with an
empirical formula of SCl. Draw the Lewis dot structure for this compound so that the formal
charges on all elements is zero.
Ch. 8 and 9 : Ws – obj 17-26-3
11. Write Lewis structures that obey the octet rule for the following species. Assign the formal charge
for each central atom.
a. POC13
b. PO43-
c. SO2C12
Answers : 1. -20. kJ
2a. S-F from SF4 = 342.5 kJ/mol, S-F from SF6 = 327.5 2b. Table 8.4 values
are based on SF6. 2c. These are not the standard states of the elements fluorine and sulfur
(Standard states are F2(g) and S8(s) 3a.
3d.
8. weak  str :CH3OH<CO32-<CO2<CO ; long to short : CH3OH>CO32->CO2>CO
10.
11. Formal charges on central atom : a. P = +1 b. P = +1 c. S
= +2
Ch. 8 and 9 : Ws – obj 17-26-3