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Name______ANSWER KEY________________________________period________ap chemistry
unit 4 worksheet
1. The molecules BF3 and SO3 are both trigonal planar. Does this information completely define the bond angles of
these molecules?
No, double bonds take up more space so the bond angle will be slightly less than 120
2. List the molecular shapes which are always polar. Bent, trigonal pyramidal, see saw, t-shaped, square pyramidal
3. Give the molecular geometry, bond angles, and polarity for each of the following molecules
a. Cl2O
b. N2O
c. SO3
d. SO3 2Bent
109.5
Polar
Sp3
linear
180
nonpolar
sp
trigonal planar
120
nonpolar
sp2
trigonal pyramidal
109.5
polar
sp3
e. ICl2-
f. PF5
g. ICl3
h. CO3 2-
linear
180
Nonpolar
trigonal bipyramidal
120, 90
nonpolar
T-shaped
90
polar
j. TeF4
k. ClO3-
trigonal planar
120
nonpolar
sp2
l. PBr3
seesaw
90, 120
polar
trigonal pyramidal
109.5
polar
sp3
trigonal pyramidal
109.5
polar
sp3
i.SF6
octahedral
90
Nonpolar
4. The molecules NF3, BF3, and ClF3 all have the same molecular formulas of the type XF3, but the molecules have
different geometries. Predict the shape of each and explain the origin of the differing shapes.
NF3: trigonal pyramidal : one lone pair
BF3: trigonal planar: no lone pairs
ClF3: T-shaped: 2 lone pairs
5. The three species NH2-, NH3, and NH4+ have H-N-H bond angles of 105°, 107°, and 109° respectively. Explain the
variation in bond angles.
105 has two lone pairs on the central atom
107 has one lone pair on the central atom
109 has no lone pairs on the central atom
6. Tell the hybrid orbitals used in each molecule in question 3 (you do not need to do expanded octets)
See above
7. Give the approximate value for the indicated bond angles and tell the hybrid orbitals used in the following
molecules
a.
c.
3
1. <<109.5 sp
3. 109.5 sp3
4. <<109.5 sp3
b.
d.
2. 180 sp
5. <<109.5 sp3
6. 109.5 sp3
8. Predict whether the following molecules possess dipole moments
a. HCN
b. BF3
c. XeF4
9. What is the difference between a sigma and pi bond? Which is generally stronger?
Sigma: overlap is between nuclei
Pi: overlap is above and below nuclei
Sigma are generally stronger
d. CCl4
10. If an atom uses an sp2 hybrid orbital, how many unhybridized p orbitals in the same valence shell remain on the
atom? How many pi bonds can the atom form?
1
1
11. a. Draw the Lewis structure for methane and formaldehyde, H2CO.
b. What is the hybridization at the carbon atoms for each?
Sp3 and sp2
c. The carbon atom in methane cannot participate in multiple bonding, whereas that in formaldehyde can.
Explain this observation.
All of the p orbitals have been hybridized in methane, but in formaldehyde, there is a left over p orbital that can
create a pi bond
12. Acetone has the following Lewis structure:
a. What is the total number of valence electrons in the molecule? 24
b. How many valence electrons are used for sigma bonds? 18
c. How many valence electrons are used for pi bonds? 2
d. How many valence electrons remain in nonbonding pairs in the molecule? 4
e. What is the hybridization at the central carbon atom of the molecule? Sp2
13. a.draw the structure for acetic acid: see in class
b. What is the molecular geometry around each carbon atom? Tetrahedral, trigonal planar
c. What type of hybrid orbitals does each carbon have? sp3, sp2
14. Name three elements which . . .
a) cannot have expanded octets when it is the central atom in a molecule. C, N, O
b) do not need an octet to form stable compounds. H, Be, B
15. Is the pi bond in NO2- localized or delocalized? How do you know?
Delocalized. There is resonance
16. How many sigma bonds and pi bonds does each of the following molecules have?
a. 9 sigma and 3 pi
b. 9 sigma and 9 pi
17. What type of intermolecular forces operates between
a. All molecules London dispersion
b. Polar molecules dipole-dipole
c. The hydrogen of a polar bond and a nearby small, very electronegative atom? Hydrogen bonding
18. Put the following in order of increasing polarizability : GeCl4, CH4, SiCl4, SiH4, GeBr4
CH4, SiH4, SiCl4, GeCl4, GeBr4
19. What kind of attractive forces must be overcome to
a. Boil water hydrogen bonding and London dispersion
b. Melt KCl ionic bonds
c. Sublime I2 london dispersion
d. Boil H2S dipole dipole and London dispersion
20. The dipole moments of HCl and HI are 1.08 D and 0.44 D respectively
a. Which of these substances will have the greater dipole-dipole interaction? HCl
b. Which of these substances will have the greater London dispersion forces? HI
21. Boiling point Substance
Suggest a reason why CH3CN has a higher
231 K
C3H8
boiling point than C3H8.
355 K
CH3CN
It is polar and the C3H8 is nonpolar
22. Nitrogen and carbon monoxide have almost equal masses. Explain why the boiling point of carbon monoxide is
slightly higher than that of nitrogen
Carbon monoxide is more polarizable and so the London dispersion forces are stronger
23. Which member of the following pairs of substances would you expect to have a higher boiling point?
a. N2 or O2
b. CH4 or SiH4
c. NaCl or CH3Cl
d. CH3Cl or CH4
24. Put the following in order of increasing boiling points: CO2, O2, BaCl2, H2O, H2S
O2, CO2, H2S, H2O, BaCl2
25. Which of the following has the fewest pi bonds and is nonpolar?
a.HCCH
b.CO2
c.CO32d.N2
e.SO2
Practice FRQ
26. A student places a mixture of plastic beads consisting of polypropylene (PP) and polyvinyl chloride (PVC) in a
1.0 L beaker containing distilled water. After stirring the contents of the beaker vigorously, the student observes
that the beads of one type of plastic sink to the bottom of the beaker and the beads of the other type of plastic
float on the water. The chemical structures of PP and PVC are represented by the diagrams below, which show
segments of each polymer.
a. Given that the spacing between polymer chains in PP and PVC is similar, the beads that sink are made of
which polymer? Explain.
The PVC beads sink. The spacing between chains is similar, but a Cl atom has a greater mass than CH3
1 point is earned for the correct polymer with a correct explanation.
(b) The boiling point of liquid propene (226 K) is lower than the boiling point of liquid vinyl chloride (260 K).
Account for this difference in terms of the types and strengths of intermolecular forces present in each
liquid.
Both substances have dipole-dipole interactions and London dispersion forces (or propene is essentially nonpolar with
only LDFs while vinyl chloride has both LDFs and dipole-dipole forces). Propene contains a CH3 group, but vinyl chloride
contains a Cl atom. Vinyl chloride thus has a larger electron cloud, is more polarizable, and has a larger dipole moment.
Thus intermolecular attractions are stronger in vinyl chloride, which results in it having the higher boiling point.
1 point is earned for a discussion of intermolecular forces and for a comparison of their relative strengths.
Review
27. Write the formula for the following
a. Hydrobromic acid
b. potassium oxide
c. nitrogen dioxide
HBr
K2O
NO2
b. Ammonia
e. silver carbonate
f. iron(III) hydroxide
NH3
Ag2CO3
Fe(OH)3
c. Sulfuric acid
h. benzene
i. methane
H2SO4
C6H6
CH4
d. Aluminum sulfate
k. hydrosulfuric acid
l. ammonium chloride
Al2(SO4)3
H2S
NH4Cl
28. Write the noble gas configuration for the following
a. Sn
b. Cr
c. Fe 2+
d. Ag
2
10
2
1
5
6
[Kr]5s 4d 5p
[Ar]4s 3d
[Ar]3d
[Kr]5s14d10
29.
a. How many molecules are in 5.63 g of methane? 2.11 x 10 23 molecules
b. How many hydrogen atoms are in 5.63 g of methane? 8.47 x 10 23 hydrogen atoms
c. How many moles are in 14.5 g of aluminum sulfate? 0.0424 mol
d. What is the molar mass of iron(III) hydroxide? 106.8 g/mol
e. How many grams are in 3.20 moles of potassium sulfide? 353 g
30. Complete the following table
Symbol
136
56
# of neutrons
# of protons
# of electrons
Atomic #
Mass #
80
56
54
56
136
31
25
25
25
56
Au
120
79
79
79
199
Ca2+
21
20
18
20
41
Ba +2
56
Mn
199
41
31. A certain ion has an atomic number of 16, a mass number of 33, and 18 electrons.
a. What is the charge on the ion? -2
b. What is the identity of this ion? Sulfur
c. How many neutrons does the nucleus of this ion have? 17
32. Substance E has 29 protons, 28 electrons, and 34 neutrons. Substance F has 29 protons, 27 electrons, and 34
neutrons. Substances E and F can be categorized as…
A) different elements
B) ions
C) isotopes
D) nuclides
E) nucleons
34. Name a compound with both ionic and covalent bonds. Potassium nitrate