Name:
Nov. 28, 2005
Chemical Principles I
Third Midterm Ch 6-9
Constants:
c = 3.00 x 108 m/s ; h = 6.63 x 10-34 J-s
1) What is an orbital? (5 pts)
An orbital is a mathematical function that describes the wave-like behavior of one
electron in an atom or molecule.
2) What is the difference in energy for a hydrogen atom with its electron in a 2s
orbital and in a 2p orbital? (3 pts)
None
Edn 9, Exercises 6-51,49
Edn 10, Exercises 6-59,57
3) Calculate the frequency of radiation that has a wavelength of 955 nm. (3 pts)
c /  (3.00 x 108 m/s) / (955 x 10-9 m)
4) Calculate the energy of a photon of frequency 6.75 x 1012 s-1. (3 pts)
E = h6.63 x 10-34 J-s) x (6.75 x 1012 s-1)
5) The physical property that demonstrates the wave-like behavior of light is called
__diffraction________. (3 pts)
6) Calculate the energy of a photon that is released when the electron in hydrogen
moves from n = 6 to n = 2. (RB = 2.18 x 10-18 J) (3 pts)
E = RB (1/nf2 - 1/ni2) = 2.18 x 10-18 J (1/22 – 1/62)
7) Fill in the numerical value of quantum numbers n and l corresponding to the
following orbital designations: (4 pts)
9Ex 6-43 10Ex 6-51
Orbital
n
l
3p
3
1
2s
2
0
4f
4
3
5d
5
2
1
8) Fill in the maximum number of electrons that occupy each of the subshells in the
following table: (4 pts)
Max number e-
3d
4s
2p
5f
10
2
6
14
9Ex 6-55 10Ex 6-63
9) Write the electron configurations for the following atoms or ions, using the
appropriate noble-gas core abbreviations: (4 pts)
Electron configuration
Cs
[Xe] 6s1
Cu
[Ar] 4s1 3d10
Ni2+
[Ar] 3d8
Se2-
[Ar] 4s2 3d10 4p6
or [Kr]
10) Fill in the quantum number(s) govern the following properties of orbitals: (4 pts)
Quantum number (or numbers)
shape
l
energy
n
spin
ms
spatial orientation
ml
11) Arrange the following atoms or ions in order of increasing size: (5 pts)
Lowest, middle, highest
Ca, Mg, Be
Be, Mg, Ca
Ga, Br, Ge
Br, Ge, Ga
Se2-, Te2-, Se
Se, Se2-, Te2-
Co2+, Fe2+, Fe3+
Fe3+, Co2+, Fe2+
Ca, Ti4+, Sc3+
Ti4+, Sc3+, Ca
12) For each of the following pairs, circle the element with the higher metallic
character. (4 pts)
2
Li or Be
Li or Na
Li
Sn or P
Na
Sn
Al or B
Al
13) Predict which of the following oxides are ionic or molecular by putting the letter I
under the ionic and M under the molecular. (6 pts)
SO2, MgO, Li2O, P2O5, N2O, XeO3
M
I
I
M
M
M
14) Write a balanced equation for the reaction that occurs in the following cases: (3
pts each)
a) Potassium metal burns in an atmosphere of chlorine gas:
2 K + Cl2  2 KCl
b) Strontium oxide is added to water:
SrO + H2O  Sr(OH)2
c) Sodium metal is added to molten sulfur:
2 Na + S  Na2S
d) Iron(II) oxide reacts with phosphoric acid:
3 FeO + 2 H3PO4  Fe3(PO4)2 + 3 H2O
e) Sulfur trioxide reacts with water:
SO3 + H2O  H2SO4
f) Carbon dioxide reacts with aqueous sodium hydroxide.
CO2 + NaOH (aq)  NaHCO3 (aq)
Or CO2 + 2 NaOH (aq)  Na2CO3 (aq) + H2O
15) Write an equation (defining your symbols) that accounts for the large increase in
lattice energy in the series of isoelectronic substances KF < CaO < ScN (2 pts)
Q+ QE 
d
Q = charge on cation or anion; d = internuclear distance
16) Circle the most electronegative atom in each of the following sets: (2 pts)
(a) P, S, As, Se;
(b) Be, B, C, Si;
(c) Zn, Ga, Ge, As; (d) Na, Mg, K, Ca
17) Using bond enthalpies in the table, estimate H for the following reaction
(Calculations must be shown to receive credit: (3 pts)
3
Bond
Bond enthalpy (kJ/mol)
N - Cl
200
Cl - Cl
242
N≡N
941
Cl
2
Cl
N
N
N
+
3
Cl
Cl
Cl
H = - (Bonds formed – bonds broken)
H = -( (941 + 3x242) – (2x3x200) )
18) Draw the Lewis structure for each and predict their electron-domain name,
molecular structure, and hybrid orbital set used by the central atom: (15 pts)
All these structures were taken from the suggested exercises, except for I3-, which was
given in class. ½ pt for the correct Lewis structure and ½ pt for the correct ED name,
MS and hybrid orbital.
Lewis structure
electron-domain
molecular structure hybrid
orbital
tetrahedral
Trigonal pyramidal
sp3
linear
linear
sp
linear
linear
sp
tetrahedral
Trigonal pyramidal
sp3
octahedral
Square planar
sp3d2
BF3
Trigonal planar
Trigonal planar
sp2
CF4
tetrahedral
Trigonal pyramidal
sp3
NCl3
tetrahedral
Trigonal pyramidal
sp3
+
H3O
SCN
-
|S =C=N|
|S =C=S|
CS2
BrO3
-
-
-
ICl4
4
SF2
-
tetrahedral
bent
sp3
tetrahedral
Trigonal pyramidal
sp3
Trigonal
linear
sp3d
octahedral
octahedral
sp3d2
Trigonal planar
Trigonal planar
sp2
tetrahedral
Trigonal pyramidal
sp3
Trigonal
linear
sp3d
AlCl4
KrF2
bipyramidal
-
PCl6
SO3
2-
SO3
I3-
bipyramidal
19) Give the approximate values for the three indicated bond angles in the following
molecule: (3 pts)
1
H
O
C
H
O
2
C
3
H
H
angle 1 __120____ , angle 2 __109____ , angle 3 __109____
5
20) Use each of the Molecular Orbital diagrams to fill in the number of electrons of
+
the three species NO, NO , NO and then calculate the bond order and give the
word to describe the magnetic property. (6 pts)
a) NO
5 + 6 = 11 valence electrons
| z

x*y*
px py pz
px py pz
|| ||
x y
||
z
E
||
s
s
s
||
s
N
NO
O
Bond Order: ___2.5________
Magnetism: ____paramagnetic____
6
b) NO
5 + 6 +1 = 12 valence electrons

| z |
x* y *
px py pz
px py pz
||
||
x y
||
z
E
||
s
s
N
||
s
NO
-
s
O
Bond Order: ____2_______
Magnetism: ______ paramagnetic _________
7
+
c) NO 5 + 6 -1 = 10 valence electrons
z
x*y*
px py pz
px py pz
|| ||
x y
||
z
E
||
s
s
N
||
s
NO+
s
O
Bond Order: ___3________
Magnetism: ____diamagnetic___________________
8
BONUS Questions
1) Pose and answer a question from chapters 6-9 that you thought would be on the
exam but wasn’t. (2 pts)
2) Sketch the 1s, 2s, and 3s orbitals on the following graphs (5pts)
1
1
1



0
0
0
5
x
0
0
0
5
5
x
x
1s = e -| x |
2s = (x – 1) e -| x/2 |
3s = (x2-x +1) e -| x/3 |
3) A 1s orbital placed 1 unit to the left on the x axis has the form, e -| x +1 | and
another placed 1 unit to the right has the form, e -| x - 1|. Sketch the  MO on the
graph on the left and the * MO on the right (3 pts), and write the mathematical
function for each (5 pts).


1
1
x
x
-5
5
-1
-1
 = ___e -| x +1 | + e -| x - 1 | ____
5
-5
* = _____ e -| x +1 |
- e -| x - 1 |
____
9