Chem 341, Quiz #2B 20 points total
Your score:______of 20. Date: 9/07
Name (Last, First): _______________KEY__________________P # : _______________
Please, write and draw in legible manner. The answer the grader cannot read/understand will be considered wrong! All questions that are A/B/C/D must be
answered A/B/C/D. If you leave the window for answer empty, it means you did not answer.
Your answer
1.
What are the correct formal charges on the labeled atoms in the following structure?
H 2C
A) i, 0; ii, +2; iii, +1
2.
N
N
C
ii
iii
i
C) i, -1; ii, +1; iii, 0
B) i, -2; ii, +2; iii, 0
D) i, -1; ii, +1; iii, +1
Which of the following statements is not true regarding resonance theory?
A) Canonical forms must be correct Lewis structures.
B) Canonical forms must have same number of unpaired electrons.
C) Median of energies of all canonical forms gives the close estimation of energy of the real molecule.
D) Less prominent canonical forms usually display formal charge(s).
3.
Draw one more canonic form for 2,4-pentanedione anion displayed below. Include formal charges as well as
appropriate arrow.
O
H3C
4.
O
O
C
H
H3C
CH3
O
C
H
CH3
Ozone is a rare form of molecular oxygen that has a summary formula O3 and non-cyclic structure. Draw a Lewis
structure of ozone, place correct formal charges and draw 1 additional possible/probable canonical form (altogether 2
c. forms):
O
O
O
_____/2
Which of the following is the correct assignment of the hybridization of the carbon and nitrogen atoms of acetonitrile
(CH3CN); atom numbering is as follows C(1)H3C(2)N(3)?
A
Which of the following canonic forms is the least prominent one?
1
C
A) 2 ;
7.
Do not write
here
O
O
A) 1 = sp3, 2 = sp, 3= sp
B) 1 = sp2, 2 = sp2, 3 = sp2
C) 1 = sp2, 2 = sp, 3 = sp
D) 1 = sp3, 2 = sp2, 3 = sp2
6.
Do not write
here
_____/2
O
5.
D
3
2
C
O
B) 1 ;
C) 3 ;
O
C
C
O
D) both 2 and 3 equally
Draw energy diagram corresponding to carbon in CH3+. Do not draw electrons that come from hydrogens.
E
Do not write
here
vacant orbital
2p-orbital level
sp2
3 sigma bonds to hydrogens
2s-orbital level
CHEM341 Quiz #2, page 1
_____/2
8.
Which sentence A-D is correct regarding the two forms below?
?
O
O
A)
B)
C)
D)
9.
O
O
These two forms are not canonical forms contributing to the same resonance hybrid.
These two forms are valid canonical forms.
These two forms are not canonical forms.
These two forms are canonical forms contributing to same resonance hybrid, but the one with two unpaired
electrons is a minor contributor.
Draw a Lewis structure of hydrazoic acid (i.e. hydrogen azide H-N3. N3 anion is not cyclic. Place correct formal
charges and draw 1 additional possible/probable canonical form (altogether 2 c. forms):
A
Do not write
here
_____/2
H
10.
N
N
H
N
Which of the following structures contains only sp2-hybridized atoms?
B
A
C
N
D
O
O
N
E
O
O
O
N
D
O
O
A) all of them; B) only A,B,C and D; C) all of them except D; D) all of them except C
11.
Which of the following sentences is correct about the following scheme?
A
H2C
B
H
CH2
H2C
C
H
CH2
H2C
H
CH2
A) canonic forms A and B are major contributor, C is a minor contributor for the same resonance hybrid;
B) all canonic forms A, B, and C; are correct caninic forms for the same resonance hybrid;
C) only A and B are canonic forms, C is not a valid Lewis structure;
D) only A and B are canonic forms of the same resonance hybrid;
12.
D
Which of the following structures has the wrong assignment of hybridization of the atoms?
C
A) 1; B) 4; C) 3; D) 2
13.
Which of the statements is not true about electronegativity (EN) of elements in the periodic system (PS)?
A) Boron has lower EN than hydrogen and therefore B-H bond is polarized with δ- on hydrogen atom.
B) The EN values of nitrogen and chlorine are very close or the same.
C) The EN values of hydrogen and alkaline metals are very close.
D) There is no EN assigned to noble gasses as they cannot accept/release electron.
14.
C
Which atomic orbitals of carbon overlap to form the two carbon-nitrogen π bonds of cyanide?
A) sp3 + sp3
B) sp + sp
C) p +p
D) sp2 + sp2
CHEM341 Quiz #2, page 2
C
15.
What is wrong in the following with the canonical forms A/B/C in terms of theory of resonance?
A
B
H
C
H
H
H
O
N
H
C
O
H
N
H
H
H
H
C
H
H
O
N
H
C
H
____/1
H
Answer:_________C is not a valid Lewis structure (as required by rule #1)________________________
16.
In the molecule of ammonia, draw the net molecular dipole (use correct sign).
H
____/1
N
H
H
CHEM341 Quiz #2, page 3