Ch 8-9 Practice Test Answer Key
18. Which of the atoms below is least likely to violate the octet rule?
a) Be- deficient likely b) P- can expland c)
S- can expand
d)
deficient is likely e) F- usually wants to follow octet rule to bond
B-
19. How many electrons are shown in the Lewis structure of perchlorate ion, ClO4–?
a) 30 b) 31 c) 32 d) 50 e) 51 Cl would bring 7 e-, each of the 4 O’s would
bring 6 (24 total) and -1 overall adds an electron for a total of 32
20. Which of the following is the correct Lewis structure for SOCl2? (Consider formal
charge)
a)
you can’t expand on atoms that are not central , and that is don
eon the Cl with the = here. It would have formal charges, too
b)
This would orient the atoms correctly, would give -1 on the
O and S would be +1. Overall charges work, and has the correct number of
electrons. It is the only viable option here
c)
no- you’d NEVER put Cl in the center; you’d put the LEAST
electronegative atom in the center, also, formal charges much?
d)
no- you’d NEVER put Cl in the center; you’d put the LEAST
electronegative atom in the center. also, formal charges much?
e)
no formal charges and the correct central atom but incorrect #
electrons.
21. As the bond order of a carbon-carbon bond increases, which one of the following
decreases?
a) # of electrons between the carbon atoms (increases by two when BO increases
by 1)
b) vibrational frequency of bond vibrations (more vibration and rotation with fewer
bonds)
c) bond energy (bond strength) (reverse relationship- energy increases with BO
and BS (yes, I see that I put BS)
d) bond length
22. Which of the following bonds is most polar? (remember that differences are
absolute value and that the partially negative end would be at the more
electronegative material)
a) N – Cl (3 -3) so Δ is 0: Non-polar
b)
c)
d)
e)
C – N (2.5-3) so Δ is 0.5, polar
S – S (2.5-2.5 )so Δ is 0: Non-polar
Br – Br (2.8-2.8) so Δ is 0: Non-polar
S – O so Δ is (2.5-3.5) so Δ is 1: polar, and more polar than b) above
23. Which one of the following molecules is a polar molecule?
a)
linear with no dipole
b)
the N-F bond has an electronegativity difference of 1, and are not
symmetrical across the whole molecule (it pulls down from the N between all
of the Fs)
c)
d)
linear with no net dipole
symmetrical so all dipoles cancel
24. Which of the following molecular shapes has six atoms joined to a central atom?
a) linear
d) trigonal bipyramid
b) tetrahedral
e) planar triangular
c) octahedral
25. Which molecular shape has bond angles which are not all the same?
a) linear- 180
b) tetrahedral- 109.5
c) octahedral- 90
d) planar triangular- 120 (trigonal planar is a better name)
e) trigonal bipyramid
26. What is the shape of BrI3? (28 electrons) you end up with 2 lone pairs on Br
(AX3E2)
a) square planar d) pyramidal
b) T-shaped
e) bent
c) distorted tetrahedral
27. What is the shape of the IF4– ion? (36e- with 4 bonds and 2 lone pairs, AX4E2
a) square planar d) octahedral
b) tetrahedral
e) T-shaped
c) square pyramidal
28. Which of the following is a polar species?
a) CO2 linear all polar so equal
b) PCl5 TBP, polar but all equal
c) ICl2– linear with TBP parent (AX2E3) so it is all equal
d) TeCl4 – AX4E, so TBP and not equal b/c lone pair prevents it; dipole
moment between all Cls
e) CCl4 tetrahedral all polar so equal
29. Which hybridization is associated with a steric number of 3? (3 domains)
a) sp- linear
d)
sp3d- TBP
b) sp2- trigonal pyramidal e)
sp3d2 - octahedral
c) sp3 - tetrahedral
30. The molecule BrF3 has a steric number of ___ on the central atom?
a) 3
b) 4
c) 5 b/c two lone pairs on the Br, making it TBP d)
6
31. What is the hybridization of Br in BrF3?
a) sp
b) sp2
c) sp3
d) sp3d- see #29 above
e) sp3d2
32. How many equivalent sp3d orbitals are there?
a) 3
b) 1
c) 5
d) 6
33. What type of hybridization is associated with a square planar molecular shape?
(see #29 for parent geometries related to the hybrid orbitals- sq planar has a TBP
parent)
a) sp3
d) sp3d
b) sp2
e) sp3d2
c) sp
(EC- not on the test) 34. A double bond contains ___ sigma bond(s)
and ___ pi bond(s).
a) 0, 2 b) 1, 2
c) 2, 0
d) 1, 1
35. What angle exists between orbitals in sp3d2 hybrid orbitals? (octahedral parent so
all are the same)
a) 90.0°
d) 120.0°
b) 180.0°
e) 78.5°
c) 109.5°
36. Which of the following elements is most likely to display sp3d hybridization? It must
be one that expands, so it can only be P
a) oxygen
d) carbon
b) nitrogen
e) boron
c) phosphorus
Previous AP Test Questions to try…
1982 D
(a) Draw the Lewis electron-dot structures for CO32-, CO2, and CO, including
resonance
structures
where
appropriate.
(b) Which of the three species has the shortest C-O bond length? Explain the reason
for your answer. It would be where there is the greatest bond order, CO.
(c) Predict the molecular shapes for the three species. Explain how you arrived at your
predictions. CO32- would be trigonal planar to spread out the electrons between 3
domains
CO2 would be linear to spread the electrons between 2 domains, and CO would be
linear as well (can’t be anything else with only 2 atoms)
1990 D
Use simple structure and bonding models to account for each of the following.
(a) The bond length between the two carbon atoms is shorter in C2H4 – double bond
between the Cs than in C2H6. Single bond between Cs
(b) The H-N-H bond angle is 107.5º, in NH3. The lone pairs of electrons take up space,
and more space than the N-H bond, pushing the 3 bonding domains down from the
parent tetrahedral geometry (3 bonding and one non-bonding domain)
(c) The bond lengths in SO3 are all identical and are shorter than a sulfur-oxygen single
bond. Resonance structures account for the fact that there is more than a single
bond but less than a double bond. The electrons are delocalized
(d) The I3- ion is linear. The lone pairs of electrons on the central I cause the “side” I’s
to be as far apart as possible- 180 degrees
1996 D
Explain each of the following observations in terms of the electronic structure and/or
bonding of the compounds involved.
(a) At ordinary conditions, HF (normal boiling point = 20ºC) is a liquid, whereas HCl
(normal boiling point = -114ºC) is a gas. Stronger attractions because a greater
dipole exists in Hf than in HCl
(b) Molecules of AsF3 are polar, whereas molecules of AsF5 are nonpolar. The 6Fs
would be completely symmetraical in all planes as an octahedral shape, whereas
the AsF5 can not be (TBP shape)
(c) The N-O bonds in the NO2- ion are equal in length, whereas they are unequal in
HNO2.
NO2 – has resonance structures where
HNO2 does not. (I had this backwards in the last version)-
(d) For sulfur, the fluorides SF2, SF4, and SF6 are known to exist, whereas for oxygen
only OF2 is known to exist. Because S can expand whereas O can not
1997 D
Consider the molecules PF3 and PF5.
(a) Draw the Lewis electron-dot structures for PF3 and PF5 and predict the molecular
geometry of each.
(b)
where there is no dipole overall because the
bonds are equally spread on the molecule
(b) Is the PF3 molecule polar, or is it nonpolar? Explain. Polar because 1.9 Eneg
difference is not cancelled out by geometry (pull down between all 3 Fs_- see
image above
(c) On the basis of bonding principles, predict whether each of the following
compounds exists. In each case, explain your prediction.
(i) NF5 No- N can not exand
(ii) AsF5 – yes because As can expand (TBP geometry)