Download Third exam 2010 with answers

City College, Chemistry Department
Chemistry 10301, sections E*, Prof. T. Lazaridis
Third Midterm exam, Nov. 24, 2010
Last Name: _____________________________________________
First Name: _____________________________________________
SSN last 4: ______________________________________________
Note: There are 7 questions in this exam. Fill in your answer in the blank space
provided immediately following each question. 1/2 point will be subtracted every
time you report a numerical result with an incorrect number of significant figures.
Speed of light : 2.9979 X 108 m/s
Planck's constant : 6.626 X 10-34 Js
1 amu = 1.66 x 10-24 g
En = -2.179 X 10-18 J/n2
Useful data:
1. (18) (a) (8) Write next to the following sets of quantum numbers whether
they are permissible or not (yes or no).
i) n=2
l=1
ml=1
YES
ii) n=1
l=0
ml =-1
NO
iii) n= 4 l=2 ml =-2
YES
iv) n=3
NO
l=3
ml =0
(b) (6) What is the maximal number of electrons in an atom that can have the
following quantum numbers
i) n=4 l=3 ml=-3
2
ii) n=5 l=3
14
ii) n=2 ms = -1/2
4
(c) (4) What is the maximal number of electrons that can occupy each of the
following subshells
i) 3d
10
ii) 4s
2
2. (12) (a) (3) Arrange the following atoms in order of increasing atomic
radius: F, P, S, As.
F < S < P < As
(b) (3) Based on their positions in the periodic table, circle the atom in the
following pairs that will have the larger first ionization energy:
K, Cr
O, Ne
Ge, Sn
(c) (3) Based on their positions in the periodic table, circle the atom in the
following pairs that will have the greater metallic character:
Li, Be
Sn, P
Al, B
(d) (3) The electron affinity for Br is +325 kJ/mol and for Kr -39 kJ/mol.
Explain this difference in terms of the electron configuration of the two
elements.
Br has s2p5 and Kr s2p6 configuration. It is favorable for Br to gain one
more electron to complete the octet. For Kr the extra electron would
have to go to the 5s orbital and the attraction would the nucleus would
be small compared to the electron-electron repulsion, hence electron
abstraction is unfavorable.
3. (10) (a) (5) Which radiation has higher energy: radiation from an x-ray
machine, the signal used in radio broadcasting, or light from an orange-red
neon light?
x-rays
(b) (5) What is the frequency of radiation that has a wavelength of 0.589
pm?
v= c/λ = 2.9979 X 108m/s / 0.589 X 10-12 m = 5.09 X 1020 sec-1
4. (10) What is the wavelength of a lithium atom moving at 6.5 X 105 m/s?
mass = 6.941 amu = 6.941 * 1.66X10-24 g
λ = h/mυ = 6.626 X 10-34 Js / 6.941 * 1.66X10-27 Kg * 6.5 X 105 m/s
= 8.8 X 10-14 m
5. (10) Calculate the frequency, energy, and wavelength in nm of the
radiation corresponding to a transition of an electron from n=5 to n=1 in the
H atom. In what area of the electromagnetic spectrum does this radiation
fall?
2.179X10-18(1/1 – 1/52) = 2.092X19-18 J (the energy)
energy = hv => v= 2.092X19-18 J / 6.626 X 10-34 Js = 3.157 X 1015 sec-1
λ = c/v = 9.496 X 10-8 m = 94.96 nm
(ultraviolet)
6. (25) Give the electron configuration and the orbital diagram (valence
electrons only) of the following elements or ions (use noble gas core
abbreviated notation):
a) (5) Sc
[Ar] 4s2 3d1
3d
4s
b) (5) Fe3+
[Ar] 3d5
3d
[Kr] 5s2 4d105p5
c) (5) I
5p
5s
d) (5) Se2-
[Kr]
4s
e) (5) Sn2+
4p
[Kr] 5s2 4d10
5s
7. (15) Use data from the tables of ionization energies and electron affinities
to determine whether the following reaction is endothermic or exothermic
and the enthalpy of the reaction:
Mg (g) + 2 Cl (g)  Mg2+ (g) + 2 Cl- (g)
Mg (g)  Mg+ (g) + e-
ΔH = +738 kJ
Mg+ (g)  Mg2+ + e-
ΔH = +1451 kJ
Cl + e-  Cl-
ΔH = -349 kJ
Multiply last by two and add to first two:
738 + 1451 -2 * 349 = +1491 kJ
(endothermic)