UNE CHEM 1011 FINAL EXAM
QUESTIONS WITH CORRECT ANSWERS 2026/2027
UNIVERSITY OF NEW ENGLAND | GENERAL CHEMISTRY
100 Questions with Correct Answers and Detailed Rationales | A+ Graded
UNIT 1: ATOMIC STRUCTURE AND PERIODIC TRENDS (Questions 1-12)
Q1: Which of the following electron configurations represents the ground state of a neutral
magnesium atom (atomic number 12)?
A. 1s² 2s² 2p⁶ 3s¹ 3p¹
B. [CORRECT] 1s² 2s² 2p⁶ 3s²
C. 1s² 2s² 2p⁶ 3s² 3p²
D. 1s² 2s² 2p⁶ 3s¹
Correct Answer: B
Rationale: Magnesium has atomic number 12, meaning it has 12 electrons. The ground state
electron configuration follows the Aufbau principle, filling orbitals in order of increasing energy:
1s² (2 electrons), 2s² (4 total), 2p⁶ (10 total), and finally 3s² (12 total). Option A represents an
excited state with one electron promoted to 3p. Option C represents silicon (atomic number 14).
Option D represents sodium (atomic number 11).
Q2: Which of the following elements has the highest first ionization energy?
A. Sodium (Na)
B. Magnesium (Mg)
C. [CORRECT] Chlorine (Cl)
D. Sulfur (S)
,Correct Answer: C
Rationale: Ionization energy generally increases across a period from left to right due to
increasing effective nuclear charge and decreasing atomic radius. Chlorine is furthest to the right
in period 3 among the options, giving it the highest first ionization energy. Sodium has the lowest
due to its single valence electron. Magnesium has a higher ionization energy than sodium but
lower than sulfur and chlorine.
Q3: What is the maximum number of electrons that can occupy the n=3 shell?
A. 2
B. 8
C. [CORRECT] 18
D. 32
Correct Answer: C
Rationale: The maximum number of electrons in a principal energy level (shell) is given by the
formula 2n². For n=3, the calculation is 2(3)² = 2(9) = 18 electrons. This shell contains the 3s, 3p,
and 3d subshells, holding 2 + 6 + 10 = 18 electrons total.
Q4: Which set of quantum numbers is invalid for an electron in an atom?
A. n = 2, l = 1, ml = -1, ms = +½
B. n = 3, l = 2, ml = 0, ms = -½
C. [CORRECT] n = 3, l = 3, ml = -2, ms = +½
D. n = 4, l = 0, ml = 0, ms = -½
Correct Answer: C
Rationale: The angular momentum quantum number (l) must be less than the principal quantum
number (n). For n = 3, the possible values for l are 0, 1, and 2. Option C states l = 3, which is
impossible because l must be less than n. Option A describes a 2p electron; Option B describes a
3d electron; Option D describes a 4s electron.
,Q5: An element has the electron configuration [Ar] 4s² 3d⁵. What is the identity of the element
and is it paramagnetic or diamagnetic?
A. Manganese (Mn), Diamagnetic
B. [CORRECT] Manganese (Mn), Paramagnetic
C. Chromium (Cr), Paramagnetic
D. Iron (Fe), Diamagnetic
Correct Answer: B
Rationale: The configuration [Ar] 4s² 3d⁵ corresponds to Manganese (Mn), which has 25
electrons. Paramagnetism occurs when an atom contains unpaired electrons. In the 3d subshell,
there are 5 electrons. According to Hund's rule, these five electrons occupy all five d orbitals
singly before pairing. Therefore, there are 5 unpaired electrons, making the atom paramagnetic.
Option C (Cr) has the configuration [Ar] 4s¹ 3d⁵.
Q6: Which of the following correctly lists the species in order of increasing atomic/ionic radius?
A. Na < Na⁺ < K
B. [CORRECT] Na⁺ < Na < K
C. K < Na < Na⁺
D. Na⁺ < K < Na
Correct Answer: B
Rationale: Cations are always smaller than their neutral parent atoms because they have lost an
electron shell and have a higher effective nuclear charge pulling the remaining electrons closer
(Na⁺ < Na). Atomic radius increases moving down a group on the periodic table, so Potassium
(K) is larger than Sodium (Na) because it has an additional electron shell. Thus, the order is Na⁺
< Na < K.
Q7: Consider the photoelectron spectroscopy (PES) spectrum of an element. A peak at a very
high binding energy (far left of spectrum) represents:
, A. Valence electrons, because they are held most loosely.
B. [CORRECT] Core electrons, because they are closest to the nucleus and most difficult to
remove.
C. Electrons in the highest energy orbital.
D. Electrons with the lowest ionization energy.
Correct Answer: B
Rationale: In PES, binding energy corresponds to the energy required to remove an electron.
Core electrons (inner shell electrons) are located closer to the nucleus and experience a higher
effective nuclear charge with less shielding. Therefore, they require significantly more energy to
remove, resulting in peaks at high binding energies (left side of the spectrum). Valence electrons
are on the right side (low binding energy).
Q8: Calculate the atomic mass of silicon if 92.23% exists as Si-28 (27.9769 amu), 4.67% exists
as Si-29 (28.9765 amu), and 3.10% exists as Si-30 (29.9738 amu).
A. 28.00 amu
B. [CORRECT] 28.09 amu
C. 28.98 amu
D. 29.00 amu
Correct Answer: B
Rationale: Atomic mass is the weighted average of isotopic masses.
Calculation: (0.9223 × 27.9769) + (0.0467 × 28.9765) + (0.0310 × 29.9738)
= 25.803 + 1.353 + 0.929
= 28.085 amu, which rounds to 28.09 amu.
Q9: Which statement regarding the shielding effect and effective nuclear charge (Zeff) is correct?
A. Zeff is higher for valence electrons than core electrons.
QUESTIONS WITH CORRECT ANSWERS 2026/2027
UNIVERSITY OF NEW ENGLAND | GENERAL CHEMISTRY
100 Questions with Correct Answers and Detailed Rationales | A+ Graded
UNIT 1: ATOMIC STRUCTURE AND PERIODIC TRENDS (Questions 1-12)
Q1: Which of the following electron configurations represents the ground state of a neutral
magnesium atom (atomic number 12)?
A. 1s² 2s² 2p⁶ 3s¹ 3p¹
B. [CORRECT] 1s² 2s² 2p⁶ 3s²
C. 1s² 2s² 2p⁶ 3s² 3p²
D. 1s² 2s² 2p⁶ 3s¹
Correct Answer: B
Rationale: Magnesium has atomic number 12, meaning it has 12 electrons. The ground state
electron configuration follows the Aufbau principle, filling orbitals in order of increasing energy:
1s² (2 electrons), 2s² (4 total), 2p⁶ (10 total), and finally 3s² (12 total). Option A represents an
excited state with one electron promoted to 3p. Option C represents silicon (atomic number 14).
Option D represents sodium (atomic number 11).
Q2: Which of the following elements has the highest first ionization energy?
A. Sodium (Na)
B. Magnesium (Mg)
C. [CORRECT] Chlorine (Cl)
D. Sulfur (S)
,Correct Answer: C
Rationale: Ionization energy generally increases across a period from left to right due to
increasing effective nuclear charge and decreasing atomic radius. Chlorine is furthest to the right
in period 3 among the options, giving it the highest first ionization energy. Sodium has the lowest
due to its single valence electron. Magnesium has a higher ionization energy than sodium but
lower than sulfur and chlorine.
Q3: What is the maximum number of electrons that can occupy the n=3 shell?
A. 2
B. 8
C. [CORRECT] 18
D. 32
Correct Answer: C
Rationale: The maximum number of electrons in a principal energy level (shell) is given by the
formula 2n². For n=3, the calculation is 2(3)² = 2(9) = 18 electrons. This shell contains the 3s, 3p,
and 3d subshells, holding 2 + 6 + 10 = 18 electrons total.
Q4: Which set of quantum numbers is invalid for an electron in an atom?
A. n = 2, l = 1, ml = -1, ms = +½
B. n = 3, l = 2, ml = 0, ms = -½
C. [CORRECT] n = 3, l = 3, ml = -2, ms = +½
D. n = 4, l = 0, ml = 0, ms = -½
Correct Answer: C
Rationale: The angular momentum quantum number (l) must be less than the principal quantum
number (n). For n = 3, the possible values for l are 0, 1, and 2. Option C states l = 3, which is
impossible because l must be less than n. Option A describes a 2p electron; Option B describes a
3d electron; Option D describes a 4s electron.
,Q5: An element has the electron configuration [Ar] 4s² 3d⁵. What is the identity of the element
and is it paramagnetic or diamagnetic?
A. Manganese (Mn), Diamagnetic
B. [CORRECT] Manganese (Mn), Paramagnetic
C. Chromium (Cr), Paramagnetic
D. Iron (Fe), Diamagnetic
Correct Answer: B
Rationale: The configuration [Ar] 4s² 3d⁵ corresponds to Manganese (Mn), which has 25
electrons. Paramagnetism occurs when an atom contains unpaired electrons. In the 3d subshell,
there are 5 electrons. According to Hund's rule, these five electrons occupy all five d orbitals
singly before pairing. Therefore, there are 5 unpaired electrons, making the atom paramagnetic.
Option C (Cr) has the configuration [Ar] 4s¹ 3d⁵.
Q6: Which of the following correctly lists the species in order of increasing atomic/ionic radius?
A. Na < Na⁺ < K
B. [CORRECT] Na⁺ < Na < K
C. K < Na < Na⁺
D. Na⁺ < K < Na
Correct Answer: B
Rationale: Cations are always smaller than their neutral parent atoms because they have lost an
electron shell and have a higher effective nuclear charge pulling the remaining electrons closer
(Na⁺ < Na). Atomic radius increases moving down a group on the periodic table, so Potassium
(K) is larger than Sodium (Na) because it has an additional electron shell. Thus, the order is Na⁺
< Na < K.
Q7: Consider the photoelectron spectroscopy (PES) spectrum of an element. A peak at a very
high binding energy (far left of spectrum) represents:
, A. Valence electrons, because they are held most loosely.
B. [CORRECT] Core electrons, because they are closest to the nucleus and most difficult to
remove.
C. Electrons in the highest energy orbital.
D. Electrons with the lowest ionization energy.
Correct Answer: B
Rationale: In PES, binding energy corresponds to the energy required to remove an electron.
Core electrons (inner shell electrons) are located closer to the nucleus and experience a higher
effective nuclear charge with less shielding. Therefore, they require significantly more energy to
remove, resulting in peaks at high binding energies (left side of the spectrum). Valence electrons
are on the right side (low binding energy).
Q8: Calculate the atomic mass of silicon if 92.23% exists as Si-28 (27.9769 amu), 4.67% exists
as Si-29 (28.9765 amu), and 3.10% exists as Si-30 (29.9738 amu).
A. 28.00 amu
B. [CORRECT] 28.09 amu
C. 28.98 amu
D. 29.00 amu
Correct Answer: B
Rationale: Atomic mass is the weighted average of isotopic masses.
Calculation: (0.9223 × 27.9769) + (0.0467 × 28.9765) + (0.0310 × 29.9738)
= 25.803 + 1.353 + 0.929
= 28.085 amu, which rounds to 28.09 amu.
Q9: Which statement regarding the shielding effect and effective nuclear charge (Zeff) is correct?
A. Zeff is higher for valence electrons than core electrons.
