MSU CEM 141 FINAL EXAM AND STUDY GUIDE
NEWEST 2026 TEST BANK| MSU CEM 141 FINAL EXAM
PREP WITH COMPLETE 550 REAL EXAM QUESTIONS
AND CORRECT VERIFIED ANSWERS/ ALREADY
GRADED A+ (MOST RECENT!!)
1. Which statement best explains why atomic radius decreases
from left to right across a period?
A) The number of electron shells increases
B) The effective nuclear charge (Zeff) increases
C) The shielding effect increases significantly
D) Electrons begin pairing in orbitals
Correct Answer: B
Rationale: As protons are added across a period without adding
new shells, Zeff increases, pulling electrons closer to the nucleus.
2. According to Coulomb’s law, if the distance between two
charged particles is halved, the force between them:
A) Doubles
B) Quadruples
C) Halves
D) Remains the same
Correct Answer: B
1
,Rationale: F ∝ 1/r², so halving r (×½) increases force by factor
of 4 because (1/(½)² = 4).
3. Which electron configuration represents a ground-state
atom of magnesium (atomic number 12)?
A) 1s² 2s² 2p⁶ 3s¹ 3p¹
B) 1s² 2s² 2p⁶ 3s²
C) 1s² 2s² 2p⁶ 3s¹ 3d¹
D) 1s² 2s² 2p⁵ 3s²
Correct Answer: B
Rationale: Magnesium has 12 electrons; the ground-state
configuration fills 1s, 2s, 2p, then 3s².
4. Which element has the highest first ionization energy in
period 3?
A) Na
B) Cl
C) Ar
D) Si
Correct Answer: C
Rationale: Ionization energy increases left to right; Ar has the
highest Zeff and a full valence shell, making electron removal
very difficult.
2
,5. Which quantum number differentiates between the two
electrons in the same 1s orbital?
A) n
B) l
C) mₗ
D) mₗ
Correct Answer: D
Rationale: The two electrons in a 1s orbital have opposite spins:
mₗ = +½ and -½ (Pauli exclusion principle).
6. Which set of quantum numbers is allowed?
A) n=1, l=1, mₗ=0
B) n=2, l=2, mₗ=0
C) n=3, l=2, mₗ=-2
D) n=3, l=0, mₗ=1
Correct Answer: C
Rationale: l must be ≤ n-1; mₗ ranges from -l to +l. For n=3,
l=2 (d orbital), mₗ=-2 is allowed.
7. How many unpaired electrons are in a ground-state
nitrogen atom?
A) 1
B) 2
3
, C) 3
D) 4
Correct Answer: C
Rationale: Nitrogen configuration 1s² 2s² 2p³; Hund’s rule gives
three unpaired electrons in the 2p orbitals.
8. Which statement about the Bohr model is false?
A) Electrons exist in fixed energy levels
B) Electrons can absorb energy to jump to higher levels
C) Electrons emit light when they fall to lower levels
D) Electrons travel in circular paths with continuously variable
energy
Correct Answer: D
Rationale: In the Bohr model, energies are quantized (fixed), not
continuously variable.
9. The de Broglie wavelength of an electron is inversely
proportional to its:
A) Charge
B) Mass × velocity
C) Frequency
D) Principal quantum number
Correct Answer: B
4
NEWEST 2026 TEST BANK| MSU CEM 141 FINAL EXAM
PREP WITH COMPLETE 550 REAL EXAM QUESTIONS
AND CORRECT VERIFIED ANSWERS/ ALREADY
GRADED A+ (MOST RECENT!!)
1. Which statement best explains why atomic radius decreases
from left to right across a period?
A) The number of electron shells increases
B) The effective nuclear charge (Zeff) increases
C) The shielding effect increases significantly
D) Electrons begin pairing in orbitals
Correct Answer: B
Rationale: As protons are added across a period without adding
new shells, Zeff increases, pulling electrons closer to the nucleus.
2. According to Coulomb’s law, if the distance between two
charged particles is halved, the force between them:
A) Doubles
B) Quadruples
C) Halves
D) Remains the same
Correct Answer: B
1
,Rationale: F ∝ 1/r², so halving r (×½) increases force by factor
of 4 because (1/(½)² = 4).
3. Which electron configuration represents a ground-state
atom of magnesium (atomic number 12)?
A) 1s² 2s² 2p⁶ 3s¹ 3p¹
B) 1s² 2s² 2p⁶ 3s²
C) 1s² 2s² 2p⁶ 3s¹ 3d¹
D) 1s² 2s² 2p⁵ 3s²
Correct Answer: B
Rationale: Magnesium has 12 electrons; the ground-state
configuration fills 1s, 2s, 2p, then 3s².
4. Which element has the highest first ionization energy in
period 3?
A) Na
B) Cl
C) Ar
D) Si
Correct Answer: C
Rationale: Ionization energy increases left to right; Ar has the
highest Zeff and a full valence shell, making electron removal
very difficult.
2
,5. Which quantum number differentiates between the two
electrons in the same 1s orbital?
A) n
B) l
C) mₗ
D) mₗ
Correct Answer: D
Rationale: The two electrons in a 1s orbital have opposite spins:
mₗ = +½ and -½ (Pauli exclusion principle).
6. Which set of quantum numbers is allowed?
A) n=1, l=1, mₗ=0
B) n=2, l=2, mₗ=0
C) n=3, l=2, mₗ=-2
D) n=3, l=0, mₗ=1
Correct Answer: C
Rationale: l must be ≤ n-1; mₗ ranges from -l to +l. For n=3,
l=2 (d orbital), mₗ=-2 is allowed.
7. How many unpaired electrons are in a ground-state
nitrogen atom?
A) 1
B) 2
3
, C) 3
D) 4
Correct Answer: C
Rationale: Nitrogen configuration 1s² 2s² 2p³; Hund’s rule gives
three unpaired electrons in the 2p orbitals.
8. Which statement about the Bohr model is false?
A) Electrons exist in fixed energy levels
B) Electrons can absorb energy to jump to higher levels
C) Electrons emit light when they fall to lower levels
D) Electrons travel in circular paths with continuously variable
energy
Correct Answer: D
Rationale: In the Bohr model, energies are quantized (fixed), not
continuously variable.
9. The de Broglie wavelength of an electron is inversely
proportional to its:
A) Charge
B) Mass × velocity
C) Frequency
D) Principal quantum number
Correct Answer: B
4
