NAME:
Midterm Exam 3
Chemistry 211
April. 4, 2005
PAGE 1 0f 6
- Show all work or NO CREDIT will be awarded.
- Work problems to proper number of significant figures.
- Be sure to include units in your answers.
- Circle your final answers.
- Put your name on ALL pages.
- Multiple choice questions are worth 4 pts. each.
1. The human eye receives a 3.65 x 10-17 J signal from photons whose wavelength is 515
nm. How many photons have hit the eye.
a) 94.9
b) 95
c) 98.3
d) 210
e) 16
2. The number of nodes in a 3s orbital is:
(a) 3
(b) 2
(c) 1
(d) 9
3. Which one of the following represents an incorrect set of quantum numbers for an
electron in an atom (arranged as n, l, ml, and ms)?
a) 2, 1, -1, -1/2
c) 3, 2, -1, 1/2
b) 1, 1, 0, 1/2
d) 5, 4, -1, 1/2
4. How many orbitals are there in the 4f subshell?
a) 4
c) 6
e) 7
b) 3
d) 5
5. In which of the following atoms is the 1s orbital the smallest?
a) Cl
b) B
c) Br
d) I
e) the 1s orbitals in all of these atoms are the same size
6. In which choice below are the elements ranked in order of decreasing atomic radius.
a) Mg, Na, P, Si, Ar
c) Si, P, Ar, Na, Mg
b) Ar, Si, P, Na, Mg
e) Na, Mg, Si, P, Ar
7. Which of the following elements has the most exothermic electron affinity?
a) Na
c) Cl
e) F
b) Li
d) N
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8. Which of the following is the electron configuration for the Br- ion?
a) [Ar]4s2 4p6
c) [Kr]4s2 4p2
b) [Ar]4s2 4p2
d) [Ne]3s2 3p6
9. Which ion in the isoelectronic series below has the smallest radius?
a) Al3+
c) O2e) N3-
d) F
-
b) Na+
10. How many resonance structures can be drawn for CO3 2-?
a) 1
b) 2
c) 3
d) 4
e) none of the above
11. Which of the following bonds is most polar?
a) S-Cl
b) S-Br
c) Se-Cl
d) Se-Br
e) Br-Br
12. Which molecule below will contain a double bond in its Lewis dot structure?
a) H2 CO
b) F2
c) H2 O
d) CH4
e) NaCl
13. What is the lowest-numbered principal shell in which d orbitals are found?
a) 1
c) 3
e) 5
b) 2
d) 4
14. Given the following bond energies in kJ/mole:
HCl = 431, HF = 567, F−F = 155, Cl−Cl = 242, H−H =432
determine the ΔHrx for the following:
(a) -359 kJ
(b) -223 kJ
2HCl(g) + F2(g) → 2HF(g) + Cl2(g)
(c) 359 kJ
2
(d) 223 kJ
15. A typical triple bond consists of
a) three sigma bonds
b) three pi bonds
c) one sigma and two pi bonds
d) two sigma and one pi bond
e) none of the above
f)
16. Which one of the following represents an incorrect set of quantum numbers for an
electron in an atom (arranged as n, l, ml, and ms)?
a) 2, 1, -1, -1/2
b) 1, 0, 0, 1/2
c) 3, 2, -1, 1/2
d) 5, 4, -5, 1/2
17. Of the bonds C-N, C=N, and C≡N, the C-N bond is
a) strongest / shortest
b) strongest / longest
c) weakest / shortest
d) weakest / longest
18. What happens to the wavelength of a beam of electrons if its speed is doubled?
a) It doubles.
b) It increases by a factor of four.
c) It decreases by a factor of two.
d) It decreases by a factor of four.
HELPFUL EQUATIONS:
Δ(mv) * Δ (x) > h
Δ En = -RH/n2 (For hydrogen)
λ = h/(mv)
E = hν
λν = c
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16. (5 pts.) Molybdenum metal must absorb radiation with a minimum frequency of 1.09 x
101 5 s-1 before it can emit an electron from its surface via the photoelectron effect.
Electrons were ejected from the metal with 3.62 x 10-19 J of excess kinetic energy when a laser
beam hit the metal’s surface. Find the wavelength of the laser light.
hc
hc
= hν + KE ⇒ λ =
λ
hν + KE
(6.6 x 10-34 J • s)(3.0 x 108 m/s)
λ =
(6.6 x 10 -34 J • s)(1.09 x 101 5s-1 ) + 3.62 x 10-19 J
λ = 1.83 x 10-7 m = 183 nm
17. (9 pts.) Write the Lewis electron dot structures for the following. Specify formal
charges and at least 3 resonance structures, if applicable.
a) SnCl6 2-
#e- = (6 x 7) + 4 + 2 = 48 = 24 e- pair
FC(Cl) = 7 – 6 – 1/2(2) = 0
FC(Sn) = 4 – 1/2(12) = -2
b) SO4 2#e- = (4 x 6) + 6 + 2 = 32 = 16 e- pair
FC(O) = 6 –6 –1/2(2) = -1
FC(O) = 6 – 1/2(8) = +2
c) OCl2
#e- = (2 x 7) + 6 = 20 =10 e- pair
FC(O) = 6 –6 –1/2(2) = -1
1
2
FC(Cl1 ) = 7 - 4 – 1/2(4) = +1
FC(Cl2 ) = 7 – 6 – 1/2(2) = 0
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18.(6 pts.) Indicate the oxidation states of the elements that undergo a change in oxidation
state in each of the following reactions.
a) MnO2 (s) + 4HCl(aq) → MnCl2 (aq) + Cl 2 (aq) + 2H2 O(l)
Cl : -1  0 oxidized
Mn: +4  +2 reduced
b) 2H 2O 2 (aq) → 2H2 O(l) + O2 (g)
O: -1  0 oxidized
O: -1  -2 reduced
c) 2CH 4 + O2 (g) → 2CH3 OH(g)
C: -4  -2 oxidized
O: 0  -2 reduced
19.(6 pts.) Chlorophyll absorbs blue light, λ = 460 nm, and emits red light, λ = 660 nm.
Calculate the net energy change in the chlorophyll system (in kilojoules) when a
mole of 460 nm photons is absorbed and a mole of 660 nm photons is emitted.
E=
hc
λ
1
1 
1
1

ΔE = hc 
= (6.6 x 10-34 J • s)(3.0 x 108 m/s) 
-9
-9
 660 x 10 m
 λ1
λ2 
460 x 10 m 
ΔE = 1.30 x 10 -19 J/molecule = 78.5 kJ/mol
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(10 pts.) EXTRA CREDIT. The energy levels of one-electron ions, such as He+ and Li2+, are
given by the equation:
En = −
(2.18x10 −18 J)Z 2
n2
where Z is the atomic number.
(4 pts.) a. Calculate the ionization energy of He+.
1
 1
ΔE = - (2.18 x 10-18 J) x 22  2 - 2  = 8.72 x 10-18 J
∞
1
(3 pts.) b. Calculate the wavelength of light required to excite a Li2+ ion from its 1s ground state
to a 4p state.
1
1
ΔE = - (2.18 x 10-18 J) x 32  2 - 2  = 1.84 x 10 -17J
4
1 
E=
hc
hc
(6.6 x 10-34 J • s)(3.0 x 108 m/s)
⇒ λ =
=
= 10.10 nm
λ
E
1.84 x 10-17 J
(3 pts.) c. When beryllium is heated, an excited Be3+ ion is created. Calculate the frequency of
light emitted when a Be3+ ion undergoes a transition from a 6f state to a 3d state.
1
1
ΔE = - (2.18 x 10-18 J) x 42  2 - 2  = - 2.91 x 10 -18J
3
6 
E
2.91 x 10-18 J
E = hν ⇒ ν =
=
= 4.40 x x 101 5s-1
-34
h
(6.6 x 10 J • s)
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