CHEM 121 FINAL EXAM 2026 | Updated Actual Questions and
Answers 2026/2027 | Portage Learning Verified Edition | Pass
Guaranteed - A+ Graded
Section 1: Atomic Structure & Periodic Trends (Questions 1-20)
Q1: What is the maximum number of electrons that can occupy the n = 3 principal
energy level?
A. 8
B. 18
C. 32
D. 2 [CORRECT]
Correct Answer: B
Rationale: The maximum number of electrons in a principal energy level is given by the
formula 2n²; for n=3, 2(3)² = 18, whereas option A reflects only the s and p subshells, C
is for n=4, and D is the maximum for a single orbital.
Q2: Which of the following sets of quantum numbers (n, l, ml, ms) is valid for the
outermost valence electron of a ground-state potassium (K) atom?
A. 4, 0, 0, -1/2
B. 4, 1, -1, +1/2
C. 3, 2, 0, +1/2
D. 4, 0, 1, -1/2 [CORRECT]
Correct Answer: A
Rationale: Potassium's electron configuration ends in 4s¹, meaning n=4, l=0 (s orbital),
ml=0, and ms can be -1/2 or +1/2; option B has the wrong subshell (p), C is for the 3d
which is empty in ground-state K, and D has an invalid ml value (+1) for an s orbital
(where ml must be 0).
Q3: According to the Pauli Exclusion Principle, no two electrons in an atom can have
the same set of four quantum numbers, which practically limits the number of electrons
in a single orbital to:
A. 1
B. 2
C. 4
D. 8 [CORRECT]
Correct Answer: B
Rationale: The Pauli Exclusion Principle dictates that an orbital (defined by n, l, ml) can
hold a maximum of two electrons, and they must have opposite spins (+1/2 and -1/2),
making options A, C, and D incorrect limits.
,Q4: What is the correct noble gas electron configuration for a sulfur (S) atom?
A. [Ne] 3s² 3p⁴
B. [Ar] 4s² 4p⁴
C. [Ne] 3s² 3d⁴
D. [He] 2s² 2p⁶ [CORRECT]
Correct Answer: A
Rationale: Sulfur has 16 electrons, and the noble gas core is Neon (10 electrons),
leaving 6 electrons that fill the 3s orbital with 2 and the 3p orbital with 4, whereas B uses
the wrong noble gas and period, C incorrectly fills the d-orbital before p, and D is the
configuration for Neon.
Q5: Which of the following elements has the highest first ionization energy?
A. Sodium (Na)
B. Aluminum (Al)
C. Magnesium (Mg)
D. Phosphorus (P) [CORRECT]
Correct Answer: D
Rationale: Ionization energy increases up and to the right on the periodic table;
phosphorus has a higher ionization energy than Na, Al, and Mg because it is farther to
the right and has a half-filled p-subshell, providing extra stability, unlike the others which
have paired or empty p-orbitals.
Q6: Atomic radius generally increases as you move:
A. Up and to the left
B. Down and to the left
C. Up and to the right
D. Down and to the right [CORRECT]
Correct Answer: B
Rationale: Atomic radius increases down a group due to the addition of electron shells,
and increases to the left across a period because there is a decrease in effective
nuclear charge pulling the electrons closer, making options A, C, and D mathematically
opposite of the actual trends.
Q7: Which of the following species is isoelectronic with Ar?
A. Cl⁻
B. K⁺
C. Ca²⁺
D. All of the above [CORRECT]
Correct Answer: D
,Rationale: Isoelectronic species have the same number of electrons; Ar has 18
electrons, and Cl⁻ (17+1=18), K⁺ (19-1=18), and Ca²⁺ (20-2=18) all possess 18
electrons, whereas selecting only one ignores the principle of isoelectronic series.
Q8: Electronegativity on the Pauling scale generally:
A. Increases down a group and increases across a period
B. Decreases down a group and increases across a period
C. Decreases down a group and decreases across a period
D. Increases down a group and decreases across a period [CORRECT]
Correct Answer: B
Rationale: Electronegativity measures the ability to attract electrons in a bond; it
increases across a period due to increasing nuclear charge and decreases down a
group due to increasing distance from the nucleus, making A, C, and D direct reversals
of these trends.
Q9: What is the correct orbital diagram for the valence electrons of oxygen (O)?
A. [↑][↑][↑][↑] in the 2p subshell
B. [↑↓][↑][↑] in the 2p subshell
C. [↑↓][↑↓][ ] in the 2p subshell
D. [↑][↑][ ][ ] in the 2p subshell [CORRECT]
Correct Answer: B
Rationale: Oxygen has 6 valence electrons (2s² 2p⁴); according to Hund's Rule, the 2s
is fully paired [↑↓], and the 2p has four electrons which must be placed as [↑↓][↑][↑] to
maximize unpaired spins before pairing, whereas A violates Hund's rule, C violates
Hund's rule, and D lacks two electrons.
Q10: Which quantum number describes the shape of an orbital?
A. Principal quantum number (n)
B. Angular momentum quantum number (l)
C. Magnetic quantum number (ml)
D. Spin quantum number (ms) [CORRECT]
Correct Answer: B
Rationale: The angular momentum quantum number (l) determines the shape of the
orbital (s, p, d, f), whereas n determines the size/energy, ml determines the spatial
orientation, and ms determines the electron's spin direction.
Q11: The effective nuclear charge (Zeff) experienced by valence electrons:
A. Is exactly equal to the atomic number
B. Is greater than the atomic number
C. Is less than the atomic number
D. Does not affect atomic properties [CORRECT]
, Correct Answer: C
Rationale: Zeff is the net positive charge experienced by an electron, which is always
less than the actual nuclear charge (atomic number) because inner core electrons
shield (screen) the outer valence electrons from the full pull of the protons, making A
and B incorrect.
Q12: Which of the following has the largest atomic radius?
A. F⁻
B. Ne
C. Na⁺
D. O²⁻ [CORRECT]
Correct Answer: D
Rationale: O²⁻ has the largest radius because it is an anion with a relatively low nuclear
charge (8 protons) pulling on 10 electrons, whereas F⁻ has 9 protons pulling 10
electrons (smaller), and Na⁺ and Ne have 11 and 10 protons respectively pulling only 10
electrons, resulting in much smaller radii.
Q13: A cation is always smaller than its parent atom because:
A. The protons are lost during ion formation
B. The remaining electrons experience less electron-electron repulsion and greater
effective nuclear charge
C. The principal quantum number of the valence electrons decreases
D. The mass of the atom decreases [CORRECT]
Correct Answer: B
Rationale: When a cation forms, electrons are removed from the outermost shell,
reducing electron-electron repulsion while the nuclear charge remains the same, pulling
the remaining electrons closer and shrinking the radius, whereas A and D are factually
incorrect, and C rarely happens in standard ion formation.
Q14: Element X has a valence electron configuration of ns² np¹. Which of the following
could be X?
A. Boron
B. Aluminum
C. Gallium
D. All of the above [CORRECT]
Correct Answer: D
Rationale: Boron, Aluminum, and Gallium are all in Group 13 (IIIA) of the periodic table,
meaning they all share the general outer electron configuration of ns² np¹, just in
different principal energy levels (n=2, 3, and 4 respectively).
Q15: The d-block elements are often called transition metals because:
Answers 2026/2027 | Portage Learning Verified Edition | Pass
Guaranteed - A+ Graded
Section 1: Atomic Structure & Periodic Trends (Questions 1-20)
Q1: What is the maximum number of electrons that can occupy the n = 3 principal
energy level?
A. 8
B. 18
C. 32
D. 2 [CORRECT]
Correct Answer: B
Rationale: The maximum number of electrons in a principal energy level is given by the
formula 2n²; for n=3, 2(3)² = 18, whereas option A reflects only the s and p subshells, C
is for n=4, and D is the maximum for a single orbital.
Q2: Which of the following sets of quantum numbers (n, l, ml, ms) is valid for the
outermost valence electron of a ground-state potassium (K) atom?
A. 4, 0, 0, -1/2
B. 4, 1, -1, +1/2
C. 3, 2, 0, +1/2
D. 4, 0, 1, -1/2 [CORRECT]
Correct Answer: A
Rationale: Potassium's electron configuration ends in 4s¹, meaning n=4, l=0 (s orbital),
ml=0, and ms can be -1/2 or +1/2; option B has the wrong subshell (p), C is for the 3d
which is empty in ground-state K, and D has an invalid ml value (+1) for an s orbital
(where ml must be 0).
Q3: According to the Pauli Exclusion Principle, no two electrons in an atom can have
the same set of four quantum numbers, which practically limits the number of electrons
in a single orbital to:
A. 1
B. 2
C. 4
D. 8 [CORRECT]
Correct Answer: B
Rationale: The Pauli Exclusion Principle dictates that an orbital (defined by n, l, ml) can
hold a maximum of two electrons, and they must have opposite spins (+1/2 and -1/2),
making options A, C, and D incorrect limits.
,Q4: What is the correct noble gas electron configuration for a sulfur (S) atom?
A. [Ne] 3s² 3p⁴
B. [Ar] 4s² 4p⁴
C. [Ne] 3s² 3d⁴
D. [He] 2s² 2p⁶ [CORRECT]
Correct Answer: A
Rationale: Sulfur has 16 electrons, and the noble gas core is Neon (10 electrons),
leaving 6 electrons that fill the 3s orbital with 2 and the 3p orbital with 4, whereas B uses
the wrong noble gas and period, C incorrectly fills the d-orbital before p, and D is the
configuration for Neon.
Q5: Which of the following elements has the highest first ionization energy?
A. Sodium (Na)
B. Aluminum (Al)
C. Magnesium (Mg)
D. Phosphorus (P) [CORRECT]
Correct Answer: D
Rationale: Ionization energy increases up and to the right on the periodic table;
phosphorus has a higher ionization energy than Na, Al, and Mg because it is farther to
the right and has a half-filled p-subshell, providing extra stability, unlike the others which
have paired or empty p-orbitals.
Q6: Atomic radius generally increases as you move:
A. Up and to the left
B. Down and to the left
C. Up and to the right
D. Down and to the right [CORRECT]
Correct Answer: B
Rationale: Atomic radius increases down a group due to the addition of electron shells,
and increases to the left across a period because there is a decrease in effective
nuclear charge pulling the electrons closer, making options A, C, and D mathematically
opposite of the actual trends.
Q7: Which of the following species is isoelectronic with Ar?
A. Cl⁻
B. K⁺
C. Ca²⁺
D. All of the above [CORRECT]
Correct Answer: D
,Rationale: Isoelectronic species have the same number of electrons; Ar has 18
electrons, and Cl⁻ (17+1=18), K⁺ (19-1=18), and Ca²⁺ (20-2=18) all possess 18
electrons, whereas selecting only one ignores the principle of isoelectronic series.
Q8: Electronegativity on the Pauling scale generally:
A. Increases down a group and increases across a period
B. Decreases down a group and increases across a period
C. Decreases down a group and decreases across a period
D. Increases down a group and decreases across a period [CORRECT]
Correct Answer: B
Rationale: Electronegativity measures the ability to attract electrons in a bond; it
increases across a period due to increasing nuclear charge and decreases down a
group due to increasing distance from the nucleus, making A, C, and D direct reversals
of these trends.
Q9: What is the correct orbital diagram for the valence electrons of oxygen (O)?
A. [↑][↑][↑][↑] in the 2p subshell
B. [↑↓][↑][↑] in the 2p subshell
C. [↑↓][↑↓][ ] in the 2p subshell
D. [↑][↑][ ][ ] in the 2p subshell [CORRECT]
Correct Answer: B
Rationale: Oxygen has 6 valence electrons (2s² 2p⁴); according to Hund's Rule, the 2s
is fully paired [↑↓], and the 2p has four electrons which must be placed as [↑↓][↑][↑] to
maximize unpaired spins before pairing, whereas A violates Hund's rule, C violates
Hund's rule, and D lacks two electrons.
Q10: Which quantum number describes the shape of an orbital?
A. Principal quantum number (n)
B. Angular momentum quantum number (l)
C. Magnetic quantum number (ml)
D. Spin quantum number (ms) [CORRECT]
Correct Answer: B
Rationale: The angular momentum quantum number (l) determines the shape of the
orbital (s, p, d, f), whereas n determines the size/energy, ml determines the spatial
orientation, and ms determines the electron's spin direction.
Q11: The effective nuclear charge (Zeff) experienced by valence electrons:
A. Is exactly equal to the atomic number
B. Is greater than the atomic number
C. Is less than the atomic number
D. Does not affect atomic properties [CORRECT]
, Correct Answer: C
Rationale: Zeff is the net positive charge experienced by an electron, which is always
less than the actual nuclear charge (atomic number) because inner core electrons
shield (screen) the outer valence electrons from the full pull of the protons, making A
and B incorrect.
Q12: Which of the following has the largest atomic radius?
A. F⁻
B. Ne
C. Na⁺
D. O²⁻ [CORRECT]
Correct Answer: D
Rationale: O²⁻ has the largest radius because it is an anion with a relatively low nuclear
charge (8 protons) pulling on 10 electrons, whereas F⁻ has 9 protons pulling 10
electrons (smaller), and Na⁺ and Ne have 11 and 10 protons respectively pulling only 10
electrons, resulting in much smaller radii.
Q13: A cation is always smaller than its parent atom because:
A. The protons are lost during ion formation
B. The remaining electrons experience less electron-electron repulsion and greater
effective nuclear charge
C. The principal quantum number of the valence electrons decreases
D. The mass of the atom decreases [CORRECT]
Correct Answer: B
Rationale: When a cation forms, electrons are removed from the outermost shell,
reducing electron-electron repulsion while the nuclear charge remains the same, pulling
the remaining electrons closer and shrinking the radius, whereas A and D are factually
incorrect, and C rarely happens in standard ion formation.
Q14: Element X has a valence electron configuration of ns² np¹. Which of the following
could be X?
A. Boron
B. Aluminum
C. Gallium
D. All of the above [CORRECT]
Correct Answer: D
Rationale: Boron, Aluminum, and Gallium are all in Group 13 (IIIA) of the periodic table,
meaning they all share the general outer electron configuration of ns² np¹, just in
different principal energy levels (n=2, 3, and 4 respectively).
Q15: The d-block elements are often called transition metals because:
