ROBINSON/FALL 2005/CHM 235
EXAM 1
NAME ______________________ No. ___
ANSWER 10 OF THE FOLLOWING 11 QUESTIONS. EACH PROBLEM IS WORTH 10 PTS.
"X" OUT THE PROBLEM YOU DO NOT WANT ME TO GRADE
1) Consider nitrous acid: HONO.
a) (3 pt) Determine the number of valence electrons in HONO.
b) (4 pt) Draw a valid Lewis structure for HONO that has zero formal charge on all atoms. SHOW
ALL BONDING ELECTRONS AND LONE PAIRS.
c)
(3 pt) Give the hybridization of nitrogen and EACH oxygen in the Lewis structure.
2) (2 pt each) Consider the following molecule:
a)
How many sp3 carbons are in the molecule? _________
2
b) How many sp carbons are in the molecule? _________
c)
How many sp carbons are in the molecule? __________
H
H
C C C C O H
H
H
H
d) What is the hybridization of oxygen? ___________
e)
How many pi bonds are in the molecule? _________
1
H
H
3) Consider the following PAIRS of molecules. All lone pairs are shown.
a) In each pair, indicate if the two structures are resonance forms of a single species (answer
YES) or if they are different species (answer NO).
b) Assign ALL NON-ZERO formal charges to EACH atom in the six structures.
Resonance forms?
(Answer Yes or No)
?
N
N
N
N
N
N
N
N
N
N
N
N
________________ (4 pt)
?
O
O
NH2
H
________________ (3 pt)
?
H
NH2
H
H
H
H
H
H
________________ (3 pt)
H
4) a) (8 pt) Draw a more stable resonance structure for the following species. USE ARROWS TO
SHOW HOW THE RESONANCE STRUCTURE IS FORMED. (All lone pairs and non-zero
formal charges are shown).
H
C
H
N
N H
H
b) ( 2 pt) Explain why the second resonance structure is more stable.
2
5) Acid/base chemistry
a) Predict products for the following Lewis acid/base reactions. INCLUDE THE ARROWS
THAT SHOW FORMATION OF THE PRODUCT. Show ALL NON-ZERO formal charges
on the products.
4 pt
CH3OH
3 pt
BH3
+
AlCl3
H3C N CH3
+
CH3
3 pt
NH3
H3C C CH2NH2
CH3
6) Complete the following acid/base reactions, filling in the reactants or products as indicated. For
each reaction, indicate if KA will be greater than or less than 1.
pKA
36
16
15.74
9.31
4.76
3.45
-1.3
-7.0
NH3
CH3CH2OH
H2O
HCN
CH3COOH
HF
HNO3
HCl
Acid
HCN
Base
+
Conjugate Acid
CH3CH2ONa
CH3COOH
NH3
+
Conjugate Base
KNO3
3
+
Cl-
Is KA > 1
or < 1?
7) Answer the following questions (2 pt each)
a) Name two atoms that have two valence electrons in p orbitals __________________
b) What is the electronic configuration for atomic oxygen? __________________________
c)
What is the valence for nitrogen? ________________________
d) In methane (CH4), each C-H bond is the overlap of what two orbitals? ________________
e)
List all of the carbon atomic orbitals that hybridized to form the sp 2 carbon in ethane (H2C=CH2):
___________________________________
8) (10 pt) Assign all non-zero formal charges in the following molecules:
H
H
H
H
C C C C
H
H
H O C
H
H H
CH3
N CH2Cl
CH3CH2
O
H
9) Consider the following molecule (lone pairs are not shown).
a) How many pi bonds are there in the molecule? _______________
b) How many carbons are sp hybridized? _________________
c)
How many carbons are sp3 hybridized? _____________
d) How many nitrogens are sp2 hybridized? _____________
e)
Draw in all hidden lone pairs. There is no formal charge on any atom in the molecule.
CH3
CH3
N C C N N C C N
CH3
CH3
4
10) Draw a stick structure for the following Kekule structure.
CH3
CH3CH2CH2CH CHCHCH2CH2Br
11) Consider the following molecule.
a)
(3 pt) How many carbons are in the molecule? _____________
b) (3 pt) How many hydrogens are in the molecule? ___________________
c)
(4 pt) Name two functional groups in the molecule. ________________ and ______________
CH2COOH
5