Midterm 2 Practice Exam.
Please note. Everything that we talked about in class is testable. This should not be considered an all-inclusive list of
topic to know but rather is to give you a feel for how I write test question. Just because a topic isn’t included here,
doesn’t mean I can’t test on it, it simply means I didn’t write an example question on it. Please study your homework,
the slides, videos, worksheets and discussion worksheets.
The Hydrogen Atom:
The Pfund series consists of spectroscopic lines in the IR region of the electromagnetic spectrum caused by the electron
moving to the n=5 level. If an emitted photon in the IR region has a wavelength of 7460nm, what was the initial energy
level? Would you expect the emission of a photon caused by the first transition in the Balmer series (nf=2) to be a higher
or lower energy?
6, higher
If an electron falls from the n=3 level to the ground state, find the wavelength of the emitted light.
103nm (note sig figs here wouldn’t be graded since it is set by how many you pick for the Rydberg constant)
If an electron goes from a n=1 to n=2 level, is a photon absorbed or emitted? Is the E positive or negative?
Going up in energy so a photon is absorbed. Since the final energy level is higher, the E is positive.
If an electron goes from a n=2 to n=1 level, is a photon absorbed or emitted? Is the E positive or negative?
Going up in energy so a photon is emitted. Since the final energy level is lower, the E is negative.
A line in the Paschen series of hydrogen has a wavelength of 1090 nm. From what state did the electron originate? (Hint:
the Paschen series all have a final energy level of 3).
6
What wavelength corresponds to the photon emitted when an electron transitions between the 4th and 2nd energy levels
in a hydrogen atom.
4.9x10-7m
Other Topics in Quantum Mechanics.
A fluorescence microscopy experiment involving GFP labelled proteins emits light at 509 nm. Assume all light from GFP
emits at this wavelength. What is the energy of the ejected photons? If the total energy emitted is 0.800 J/second, how
many proteins emit photons in that second? Briefly explain the purpose of using GFP labelled proteins.
3.90x10-19 J, 2.05x1018 photons Tag proteins to locate it by watching emission events.
are many ways to discuss this.
Or anything else correct, there
What are some applications of spectroscopy in science?
(this is an exceptionally open ended question, we covered many in class including flame tests, detecting elements far
away from us in space, and the use of the Green Fluorescent protein. The book covers how “neon” (which are really
made of several elements) lights work, and there are many others that we didn’t talk about (like fireworks). You should
be able to state and explain a few applications.
Describe the difference between the terms emitted, reflected and scattered.
Emitted light comes directly from a source. For instance a blackbody radiator (space heater, incandescent light bulb),
laser, ect….. Reflected light is the light that allows us to see objects because light that has been emitted from a source
bounces off the objects. Scattered light is very similar, although is often talked about slightly differently. For instance
light from the sun scatters in the atmosphere making the sky blue.
Chapter 5.
Write the formula for each:
Calcium Phosphate
Ca3(PO4)2
Potassium Chloride: KCl
Magnesium Chloride
MgCl2
Calcium Nitrate : Ca(NO3)2
Calcium Chlorate : Ca(ClO3)2
Sodium Chloride: NaCl
Write the name for each:
CCl4
Carbon tetrachloride
H3PO4 (aq) Phosphoric acid
H3PO3
phosphorous acid
H2SO3
PCl5
phosphorous penta chloride
Sulfurous acid
A 0.105 M Na2SO4 solution is prepared. How many ions (note not mols) of sodium are present in 300. mL of the solution.
5.69x1022ions
If a sample is 80% carbon by mass and 20% hydrogen by mass, what is the empirical formula?
CH3
If the molecular mass of the molecule in the above question is 30. g/mol, what is the molecular formula?
C2H6
Electron Configurations
Which is the ground-state electron configuration of In+?
A) [Kr]4d75s25p3 B) [Kr]4d85s15p3 C) [Kr]4d55s15p6
D) [Kr]4d105s2
E) [Kr]4d105s15p1
Write the ground-state electron configuration of a neutral sulfur atom.
[Ne]3s23p4
What is the electron configuration of S2-?
[Ne]3s23p6
D
Give the electron configuration for neutral copper. Use the noble gas short hand notation.
[Ar]4s13d10
*note: remember this is an exception because a fully filled subshell is stable so one electron is promoted
from the s orbital up to the d orbital.
Give the electron configuration for neutral molybdenum. Use the noble gas short hand notation.
[Kr]5s14d5
*note: remember this is an exception because a fully filled subshell is stable so one electron is promoted
from the s orbital up to the d orbital.
Give the electron configuration for Mo+. Use the noble gas short hand notation.
[Kr]4d5
*note: remember this is an exception because a half filled subshell is stable so one electron is promoted
from the s orbital up to the d orbital.
Give the electron configuration of the +1 ion of the element given in the previous problem. Use the noble gas short hand
notation.
[Ar]3d10
*Note: remember when ever you are in the d block and want to make a + ion, you’ll remove the
electrons from the s orbital first.
Is the following electron configuration of phosphorous a ground state or excited state configuration? [Ar]3s13p4.
Excited
*Note: the ground state is [Ar]3s23p3 any time you move an electron into a higher energy level (except in
the cases of added stability from, like in the d-block exceptions) it is considered an excited state.
If a +3 ion is made from antimony, which orbital(s) are the electrons removed from? (be sure to include the energy level
and subshell)
5p
If a +4 ion is made from lead, which orbital(s) are the electrons removed from? (be sure to include the energy level and
subshell)
6p and 6s
Which of the following orbital(s) is/are most shielded (assume all listed orbitals are filled): 1s, 3s, 4d, 5s
4d
How many nodes are present in a 4s orbital?
3
Quantum Numbers
Quantum numbers: State whether each set of quantum numbers is allowed. If they are, give the missing quantum
numbers, state how many orbitals and how many electrons are present with those quantum numbers.
(book/sapling/class/reviewsheet)
A) a) n=6
i) ml=?
l=1 and 3
ii) number of orbitals?
±3, ±2, ±1, 0
10
iii) Number of electrons?
20
*note: don’t forget to do the ml for both l=1 and l=3 when it comes to counting orbitals. There are 7 from l=3, and 3 from l=1.
b) n=4
i) l=?
ml=-1, 0, 1
ii)number of orbitals?
3, 2, 1, 0
10
iii) Number of electrons?
20
*note: don’t forget that l is determined by the n value so for each possible value of l decide what ml are allowed.
l
3
2
1
0
ml for this rule set.
-1,0,1
-1,0,1
-1,0,1
0
Total of 10 orbitals.
c) n=5
l=4 ms= +1/2
i) ml=?
ii) number of orbitals?
±4, ±3, ±2, ±1, 0,
9
iii) Number of electrons?
9
Which set of quantum numbers, n, l correspond to one of the highest energy electrons in the ground state of Cobalt?
N=3, l=2
How many orbitals in a single atom may have the quantum numbers: n=5 or 4, l=3, ms=+1/2
14
How many electrons in a single atom may have the quantum numbers: n=5 or 4, l=3, ms=+1/2
14
Periodic trends
Why do electron affinity and electronegativity share the same trend? Why does electron affinity have p-block exceptions
but electronegativity does not even though they share the same trend (be specific and give one example of an exception
in your answer)?
In both cases they are based on the effective nuclear charge. Electron affinity is not only based on effective nuclear
charge but also on stable electron configurations. (they may also say something like thing, stable half shells change
electron affinity but not electronegativity).
Many Correct Examples
Which has more covalent character BeCl2 or AgF? Why? Be specific. Describe the behavior of both species in the
molecule and how each contributes to the covalent character.
First compare Ag+ and Be2+. Be2+ is smaller and higher charged so it has more polarizing power.
Then compare Cl- and F-. Cl- is larger, and therefore has more polarizability
The thing with more polar power and more polarizability has more covalent character, so BeCl2 has greater covalent
character.
Rank C, N and O in terms of increasing electron affinity. Explain the order.
N, C, O: effective nuclear charge causes it to increase as you go right on the periodic table. However C and N
are reversed because of the stability caused by the half filled p orbital in nitrogen.
Lewis Structures
For each formula, draw the lewis structure:
A) PCl3
B) BrF5
For each of the following lewis structures, decide if it is correct. If it is not, fix it. If there is resonance, only
draw one structure.
a)
b)
c)
d)
a) Incorrect use the two radical electrons to form a bond
b) incorrect, you need one oxygen on each nitrogen to have a double bond.
c) Incorrect put double bond between CO not CH leaving two lone pairs on O
d) incorrect triple bond between CN leaving one lone pair on N
How many lone pairs are found on the central atom in the Lewis structure of XeF4
2
How many double bonds are present in the “best” structure of the sulfate ion?
2
MO Theory
What is the bond order of N22- ? (hint: use MO theory).
2
Which of the following has the highest bond order? (hint: use MO theory ).
A) N2
B) O22- C) N22+
D) N22-
E) impossible to tell
A
If you add an electron to an anti- bonding orbital does it increase or decrease the bond order?
Decrease
Given that in an NO heteronuclear diatomic the 2p>2p draw the MO diagram. Is it paramagnetic or diamagnetic? What
is the bond order? Would adding an electron add or subtract from the bond order?
(Hints: remember to label both the atomic and molecular orbitals including subscripts. Include all electrons in both
atomic and molecular orbitals.)
Para/dia magnetic? _para______
Bond Order____2.5___
Add or subtract?___subtract_____
Periodic Trends
If the first ionization energy of copper is 1958 kJ·mol-1, the second ionization energy is likely to be
________________(greater or less) than 1958 kJ·mol-1.
greater
Which of the following has the largest atomic radius ? F, Na, Li, He, or N
Na
Put the following in order of INCREASING ionization energy. C, N, O.
C,O,N
Which of the following atoms is most polarizable? S, Se or Te.
Te
Order the following in terms of INCREASING atomic radius. P, N, As.
N, P, As
Order the following in terms of INCREASING electron affinity. Ti, Cr, V
Ti, V, Cr
Order the following in terms of INCREASING ionization energy. Si, P, S
Si, S, P