Inorganic Chemistry - Problem Drill 03: Atomic Structures and Electron Configuration
Question No. 1 of 10
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on paper as needed (3) Pick the answer (4) Go back to review the core concept tutorial as needed.
1. A cation is a positive ion where its atom or group of atoms has lost one or more
electrons. How many electrons does Sr2+ have?
Question
(A)
(B)
(C)
(D)
(E)
38
36
40
88
2
A. Incorrect.
This would be a neutral Sr atom.
B. Correct.
Good job! This would be for a +2 ion, with two less electrons than neutral Sr atom.
Sr2+ = 1s22s22p63s23p64s23d104p6.
C. Incorrect.
This would be a -2 ion.
Feedback
D. Incorrect.
This is using mass number rather than atomic number to determine electrons.
E. Incorrect.
The charge is the number of protons – electrons. This is not the number of
electrons.
Sr’s atomic number is 38, which means as a neutral atom it has 38 electrons.
Sr+2 has had 2 electrons removed. It now has 36 electrons with the same
electronic configuration as [Kr] or 1s22s22p63s23p64s23d104p6.
The correct answer is (B).
Solution
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Question No. 2 of 10
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needed (3) Pick the answer (4) Go back to review the core concept tutorial as needed.
2. Box Orbital Notation is one way to show electron configurations where orbitals
and spin states are clearly labeled. Which is the correct electronic configuration for
33As?
Question
(A) 1s  2s 
(B) 1s  2s 
(C) 1s  2s 
 _ __
(D) 1s  2s 
_ _
(E) 1s  2s 
 _
2p    3s  3p  _ __
2p    3s  3p _ _ _
2p    3s  3p    4s  3d      4p
2p    3s  3p    4s  3d      4p 
2p    3s  3p    4s  3d      4p
A. Incorrect.
This one doesn’t have 33 electrons.
B. Incorrect.
This one doesn’t have 33 electrons.
C. Incorrect.
This one didn’t put one electron in each 4p orbital before doubling up.
Feedback
D. Correct!
Good job! This one has the correct electrons configuration for 33As – the three outer
shell p electrons are filled in each orbital with the same spin before doubling up.
E. Incorrect.
One of the 4p orbitals is missing and two electrons are paired when they do not
need to be.
As has 33 electrons. This is the orbital box notation. According to the Hund’s Rule,
the last three p electrons must be filled in each p orbital with the same spin, not to
double up. Its long spectroscopic notation is: 1s22s22p63s23p64s23d104p3.
The correct answer is (D).
Solution
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Question No. 3 of 10
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needed (3) Pick the answer (4) Go back to review the core concept tutorial as needed.
3. The Aufbau principle is the build-up method to determine the electron
configuration of an atom, molecule or ion. Which of the following is correct for 14Si?
Question
(A) 1s2
(B) 1s2
(C) 1s2
(D) 1s2
(E) 1s2
2s2 2p6
1p6 2s2
2s2 2p4
2s2 2p2
2s2 2p6
3s2 3p2
2p4
3s2 3p4
3s2 3p2
2d8
A. Correct!
Good job! There are total of 14 electrons, filled in sequentially. The outer shell 2p
with 2 electrons on each orbital with the same spin.
B. Incorrect.
There is no 1p subshell.
C. Incorrect.
This one doesn’t have 14 electrons.
Feedback
D. Incorrect.
This one doesn’t have 14 electrons.
E. Incorrect.
There is no 2d subshell.
Si has 14 electrons. Fill them in order of 1s –> 2s –> 2p –> 3s –> 3p. The outer
shell 2p with 2 electrons on each orbital with the same spin.
The correct answer is (A).
Solution
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Question No. 4 of 10
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needed (3) Pick the answer (4) Go back to review the core concept tutorial as needed.
4. The noble gases have the most stable electron configurations since all their
subshells are filled. They are relatively inert. With their subshells all filled, noble
gases can be used as a short hand way to represent the core electrons. The valence
electrons are still explicitly written out. Write the noble gas notation for 34Se.
Question
(A) [Ar] 1s2 2s2 2p6 3s2 3p4
(B) [Ar] 4s2 3d10 4p4
(C) [Kr] 4s2 3d10 4p4
(D) [Kr] 1s2 2s2 2p6 3s2 3p4
(E) 1s2 2s2 2p6 3s2 3p4
A. Incorrect.
When using noble gas notation, you don’t start at 1s.
B. Correct!
Good job! The 34Se’s core electrons are represented by [Ar] (1s22s22p63s23p6) and
the outer shells are 4s23d104p4.
C. Incorrect.
Feedback
Remember—chose the noble gas that is closest without going over to the number of
electrons needed.
D. Incorrect.
When using noble gas notation, you don’t start at 1s.
E. Incorrect.
Use a noble gas to represent the inner electrons.
Se has 34 electrons. The noble gas closest to 34 without going over is Ar (18). The
core electrons are represented by [Ar] (1s22s22p63s23p6) and the outer shells are
4s23d104p4.
The correct answer is (B).
Solution
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Question No. 5 of 10
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needed (3) Pick the answer (4) Go back to review the core concept tutorial as needed.
5. The typical quantum mechanics model uses four quantum numbers (n, l, ml and
ms) to describe any unique electronic state of an electron. There is one invalid
quantum number set below, which one?
Question
(A) 1,
(B) 2,
(C) 3,
(D) 2,
(E) 2,
1,
0,
2,
1,
1,
-1, -½
0, +½
2, +½
1, +½
-1, +½
A. Correct.
Good job! This is for a 1p subshell (1,1), which doesn’t exist.
B. Incorrect.
This is for a 2s on line 0 with an up arrow, which is all possible.
C. Incorrect.
This for a 3d on line 2 with an up arrow, which is all possible.
Feedback
D. Incorrect.
This is for a 2p on line 1 with an up arrow, which is possible.
E. Incorrect.
This is for a 2p on line -1 with an up arrow, which is possible.
Set A is for a 1p subshell, which does not exist.
The rest of the sets are permissible.
The correct answer is (A).
Solution
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Question No. 6 of 10
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needed (3) Pick the answer (4) Go back to review the core concept tutorial as needed.
6. The electronic configuration is the distribution of electrons of an atom or
molecule in atomic or molecule orbitals. Sodium oxide is used in ceramics and
glasses. Which of the following is the electron configuration for Na in Na 2O?
Question
(A) 1s2
(B) 1s2
(C) 1s2
(D) 1s1
(E) 1s2
2s2
2s2
2s2
2s1
2s2
2p6 3s1
2p6 3s2
2p6
2p3 3s1 3p3 4s1
2p5
A. Incorrect.
This doesn’t have 10 electrons.
B. Incorrect.
This doesn’t have 10 electrons.
C. Correct!
Feedback
Good job! Sodium has 11 electrons in total. With +1, one electron is removed.
Therefore Na+ has 11 - 1 = 10 electrons. This one has 10 electrons correctly
placed.
D. Incorrect.
This one only puts half the number of electrons in each orbital that are necessary.
E. Incorrect.
This has one less electron than it should be.
Na in Na2O is Na+.
Na has 11 electrons, so Na+ will have 10 electrons.
Only answers C & D have 10 electrons.
Answer D uses only half as many electrons as possible in each subshell.
Choice E has one fewer electron.
The correct answer is (C).
Solution
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Question No. 7 of 10
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needed (3) Pick the answer (4) Go back to review the core concept tutorial as needed.
7. Aluminum (13Al) is the third most abundant element (beside oxygen and silicon)
and the most abundant metal in the Earth’s crust. Which is the correct electronic
configuration for 13Al?
Question
(A) [Ne]
(B) [He]
(C) [Ne]
(D) [He]
(E) [Ne]
3s2
3s2
1s2
1s2
2s3
3p1
3p1
2s1
2s1
A. Correct.
Good job! This one has 13 electrons with the correct noble gas configuration.
B. Incorrect.
This one doesn’t have 13 electrons. The core electrons are mis-represented by
[He].
C. Incorrect.
When using noble gas configuration, you don’t begin with 1s.
Feedback
D. Incorrect.
This one doesn’t have 13 electrons. The core electrons are mis-represented by
[He].
E. Incorrect!
This configuration has 3 electrons in an s subshell—which can only hold up to 2
electrons.
Al has 13 electrons.
Ne has 10 electrons & H has 2 electrons.
Only answers A & C have 13 electrons.
Answer D starts over with 1s, not where Ne left off.
Choice E has three electrons in an s subshell when s subshells can only hold 2
electrons.
The correct answer is (A).
Solution
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Question No. 8 of 10
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needed (3) Pick the answer (4) Go back to review the core concept tutorial as needed.
8. Electrons are built up onto the orbitals one level at a time according to the
Aufbau Principle. There are also exceptions to this rule. Which are the correct
configurations for Cu and Cu+?
Question
(A)
(B)
(C)
(D)
(E)
[Ar]3d94s2 and [Ar]3d94s1
[Ar]3d94s2 and [Ar]3d84s2
[Ar]3d104s1 and [Ar]3d10
[Ar]3d104s1 and [Ar]3d94s1
[Ne]3d104s1 and [Ne]3d10
A. Incorrect.
The 4s should not be doubled up since half-filled is more favorable.
B. Incorrect.
The 4s should not be doubled up since half-filled is more favorable.
C. Correct!
Good job! Use the half-filled rule to build up the outer shells. The removal of one
electron is from the highest occupied sublevel.
Feedback
D. Incorrect.
The neutral species is correct but the removal of electron should be on 4s first, not
3d.
E. Incorrect.
The core electrons are mis-represented. It should be [Ar].
This is an exception to the rule. Half-filled sublevels have lower energy since
unpaired electrons are more stable. 29Cu has 29 electrons with the core electrons
represented by [Ar] and the outer shell electrons are piled up as half-filled 3d104s1
for more stability. To make a cation Cu+, we need to take away one electron from
the highest energy sublevel, 4s. Therefore, Cu+ = [Ar]3d10.
The correct answer is (C).
Solution
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Question No. 9 of 10
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needed (3) Pick the answer (4) Go back to review the core concept tutorial as needed.
9. Isoelectric elements and/or ions have the same number of electrons and
configuration. Isoelectric chemical species tend to have similar chemical properties.
All pairs below are isoelectric except ___.
Question
(A)
(B)
(C)
(D)
(E)
Be2+ and He
S2- and Cl
Mg2+ and Na+
Ca+ and K
P3- and S2-
A. Incorrect.
These two species are isoelectric with the same configuration of 1s2.
B. Correct.
Good job! S2- has the configuration of 1s22s22p63s23p6 and Cl has a slightly
different configuration 1s22s22p63s23p5. They are not isoelectric pair.
C. Incorrect.
These two species are isoelectric with the same configuration of 1s22s22p6.
Feedback
D. Incorrect.
These two species are isoelectric with the same configuration of [Ne]4s1.
E. Incorrect.
These two species are isoelectric with the same configuration of 1s22s22p63s23p6.
S2- has the configuration of 1s22s22p63s33p6 and Cl has a slightly different
configuration 1s22s22p63s33p5. Each has different number of electrons.
The correct answer is (B).
Solution
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Question No. 10 of 10
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needed (3) Pick the answer (4) Go back to review the core concept tutorial as needed.
10. The four quantum numbers described an electron are the principal (n), angular
or azimuthal (l), magnetic (ml) and spin (ms). The first three quantum numbers
describe the size, shape, and orientation in space of the orbitals on an atom. The
last one (ms) describes the spin state of an electron. The possible values of each
quantum number correlate to one another. Which of the following sets of quantum
numbers (n,l,ml,ms) is not possible?
Question
(A) 1,
(B) 2,
(C) 2,
(D) 3,
(E) 4,
0,
0,
1,
2,
3,
0, -½
-1, +½
-1, +½
1, +½
-2, +½
A. Incorrect.
1s with a down arrow on line 0 is allowed.
B. Correct.
Good job! There is no -1 line in the 2s subshell. This configuration is not possible.
C. Incorrect.
2p with an up arrow on the -1 line is allowed.
Feedback
D. Incorrect.
An up arrow on the 1 line in a 3d subshell is allowed.
E. Incorrect!
An up arrow on a -2 line of the 4d subshell is allowed.
The second set is an 2s subshell. The 2s subshell only has 1 orbital, which means
that the 3rd number has to be “0”.
The correct answer is (B).
Solution
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