------------------------------------------------------------------------------------------------------2-
1B. Circle the correct answer (18 pts total) (2 points each)
O
(a) The formal charge on the S in sulfate (see right) is:
i) -2
ii) –1
iii) 0
iv) +1
O
v) +2
S
O
O
(c) The first ionization energy is predicted to be _______
i) greater for Br than F.
ii) greater for Br than Br+.
iii) greater for Br than Se.
iv) none of the above
(primarily) because the outer electrons
i) are closer to the nucleus in Br than in the other atom or ion.
ii) see a greater positive charge from the nucleus in Br than in the other atom or ion.
iii) are held less tightly in Br than in the other atom or ion.
iv) none of the above
(d) Which statement is true:
i) C-D is the weaker bond.
ii) A-B is the shorter bond
iii) both i) and ii)
iv) none of the above
A-B
Potential
Energy
Distance Between
Atoms
0
C-D
-------------------------------------(e) Which species has the most negative electron affinity?
i) O
ii) O+
iii) O2+
iv) O-
See problem 9 on PS10 for full explanation.
(f) The best reasoning for the answer to the question above is:
i) The more negative the electron affinity, the less favorable a process is.
ii) It is more favorable to add an electron to O than the other species.
iii) O- is more negative than the other species.
iv) The more positive an ion, the stronger the force of attraction for added electrons.
(e) Which species is likely to be the least likely to exist in nature for any length of time (i.e. is
the least stable)?
i) AsF4ii) PF4iii) NF4- See problem 16 on PS10, and 5b on PS11
iv) SbF4-
(f) The best reasoning for the answer to the question above is:
i) second row elements cannot stably have more than 8 electrons around it
ii) the larger the central atom, the stronger the bonding and more stable the species
iii) the smaller the electronegativity, the weaker the bonding
iv) all of the above
v) none of the above
(e) Which species is the most stable with respect to pulling an electron away from it?
i) K+
See Problems 1 and 2c on PS11—although size is stressed in the text, we related
size and ionization energy to Zeff. Also see the worksheet.
ii) Ar
iii) Cliv) all are equal in this regard
(f) The best reasoning for the answer to the question above is:
i) noble gas atom are fundamentally the most stable
ii) this species has the greatest Zeff
iii) all species have a filled shell This is true but doesn’t mean I1’s are the same!
iv) the farther to the right in the periodic table, the greater the ionization energy
2B. Write T (True) or F (False) for the following statements. If the statement is false
correct it by changing, dropping, or adding a few words (6 points)
a) Polarity is a number that reflects the tendency of an atom to pull bonding electrons to itself.
Electronegativity
b) Mg2+ is the common ion formed by Mg because the third ionization energy of Mg is
extremely large.
T
Free Response Questions-B
3B. (6 pts) Are these two Lewis structures considered equally good representations for NCF? If
not, which is better? Give your reasoning.
N
C
F
N
C
F
No. The one on the left is a better representation. Both have octets around all atoms,
but the one on the left has more “favorable” formal charges (all zero). In the structure
on the right, N has a FC of –1 and F has a formal charge of +1. (Not only are more
FC’s worse than fewer, but putting a +1 FC on a F atom is very unfavorable/unlikely
because F has the greatest electronegativity and thus it is difficult to pull electrons away
from it [to make it positive]).
4B. (16 pts) Draw Lewis structures for each of the following (include equivalent resonance
structures, if applicable:
same as SF4 on PS10 except
(a) OCl2 v = 6 + 2(7) = 20
(b)AsF4 need brackets and charge
shown. v = 5 + 4(7) + 1 = 34
Cl
O
Cl

F
(Note: If you put the Cl in the middle
because it is less electronegative, I
As
F
F
would have accepted that as well)
F
(c) NO3- v = 5 + 3(6) + 1 = 24


O
O
O
N

O
O
N
O
O
O
N
O
5B.
NCF
OCl2
AsF4NO3-
ECG
CG
(arrangement of electron
(molecular structure—
angle(s)
clouds)
arrangement of atoms)
linear
tetrahedral
trigonal
bipyramidal
trigonal planar
linear
bent
sp
sp3
180°
≤109°
see saw
sp3d (or dsp3)
≤120° and ≤180°
trigonal planar
sp2
120°
hybrid orbitals
used by center
11B. (5 pts) If the following drawings are meant to very simplistically represent the distribution
of electrons in two different atoms, predict which atom would have the greater ionization
energy, and provide your reasoning.
+19
-
2e
+18
-
2e
-
8e
-
8e
8e
8e
-
1e
-
Atom B
Atom A
Atom B would have the greater ionization energy. Its outer electrons experience an
effective nuclear charge of +8 (+18 – 2 – 8) which is much larger than the effective
nuclear charge seen by the outer electron in Atom A (+1; +19 – 2 – 8 – 8). The force of
attraction between electrons and the nucleus is given by Coulomb’s Law, so the greater
the magnitude of charge, the greater the force. And the greater the force, the harder it
is to pull the electron away, and thus the greater the energy needed (larger ionization
energy).
(Interesting note: The fact that the outer electrons are coming from a “closer” energy level in B than in A
(3rd level vs. 4th level) also plays a role since force depends on distance as well, but the 8-fold increase in Zeff
is by far the major factor. This is clear from the fact that the first IE of Xe (Zeff = +8, but outer electron
coming from the 5th energy level is still MUCH larger than the first IE of K (Zeff = +1, and outer electron
coming from the 3rd energy level). See text for values (~1200 kJ/mol for Xe vs. ~400 kJ/mol for K)
12B. (3 pts) Consider CF2O, whose structural formula is:
O
F
C
F
(a) Draw arrow symbol(s) on the Lewis dot structure to properly indicate all bond dipoles
(i.e., all polar bonds) in the molecule.
(b) Which atom will have the greatest partial negative charge? (a) C (b) F (c) O
13B ***REMEMBER TO LOOK AT PS11 AND THE VSEPR LAB FOR PRACTICE
PROBLEMS NOT REPRESENTED ON THIS PRACTICE EXAM***
F
H
H
N
H
C5
H
CG(N):__Trigonal pyramidal__(lone pair
needed to be added)_______
H-N-C3 angle:__ ≤109____
C4
Cl
CG(C1):____Trigonal planar_________
H-C1-C2 angle:__ ≤120____
CG(C3):____Tetrahedral__________
C3
O
C2
C1
H
H
N-C3 -O angle:___ 109___
CG(C5):_____Trigonal planar_________
H
O
(a) State the total number of sigma bonds and pi bonds in this molecule. :__16___
F-C5-C4 angle:__ ≤120___
:___2___
(b) State the hybrid orbitals used by each of the four centers identified above to make sigma bonds:
CG(N):_____sp3________ CG(C1):_____sp2_____ CG(C3):_____sp3______ CG(C5):_____sp2_______
(c) State the orbitals used for pi bonding for the centers that involve pi bonds. p orbitals
I’M SORRY, BUT THERE ARE NO PRACTICE EXAM PROBLEMS AVAILABLE FOR
PS12 MATERIAL. AGAIN, PLEASE LOOK AT THE PROBLEM SET 12 ANSWER KEY
AND PROBLEMS.