CHEM 121 MODULE 3 EXAM: ATOMIC
STRUCTURE AND PERIODICITY
QUESTIONS AND ANSWERS 2026/2027
UPDATE || 100% GUARANTEED PASS
1. Calculate the energy (in Joules) of a single photon of light with a wavelength of 450 nm.
A. 1.33 x 10^-15 J
B. 2.98 x 10^-27 J
C. 6.63 x 10^-34 J
D. 4.42 x 10^-19 J
Answer: D
Conceptual Explanation: Energy is calculated using E = hc/λ. E = (6.626 x 10^-34 J·s *
3.00 x 10^8 m/s) / (450 x 10^-9 m) = 4.42 x 10^-19 J.
2. Which of the following sets of quantum numbers (n, l, ml, ms) is NOT allowed?
A. 3, 2, -2, +1/2
B. 1, 1, 0, +1/2
C. 3, 0, 0, +1/2
D. 2, 1, 0, -1/2
,Answer: B
Conceptual Explanation: For n=1, the only possible value for l is 0. If n=1, l cannot be 1
because l must be less than n.
3. What is the correct ground-state electron configuration for the Copper (Cu) atom?
A. [Ar] 4s2 3d9
B. [Kr] 4s1 3d10
C. [Ar] 4s2 3d10
D. [Ar] 4s1 3d10
Answer: D
Conceptual Explanation: Copper is an exception to the Aufbau principle; it promotes one
4s electron to the 3d subshell to achieve a full 3d10 stability.
4. Which element has the highest first ionization energy?
A. Nitrogen
B. Helium
C. Fluorine
D. Oxygen
Answer: B
, Conceptual Explanation: Helium has the highest first ionization energy of all elements
due to its small radius and full valence shell.
5. The de Broglie wavelength of a particle is inversely proportional to its:
A. Charge
B. Potential energy
C. Momentum
D. Spin
Answer: C
Conceptual Explanation: The de Broglie equation is λ = h/p, where p is momentum (mass
times velocity).
6. In the photoelectric effect, if the frequency of the incident light is below the threshold
frequency:
A. Electrons are emitted with low kinetic energy
B. Electrons are emitted after a long delay
C. No electrons are emitted regardless of intensity
D. Only a few electrons are emitted
Answer: C
Conceptual Explanation: Photoemission only occurs if the photon energy (hν) exceeds the
work function. Intensity only increases the count if the threshold is met.
STRUCTURE AND PERIODICITY
QUESTIONS AND ANSWERS 2026/2027
UPDATE || 100% GUARANTEED PASS
1. Calculate the energy (in Joules) of a single photon of light with a wavelength of 450 nm.
A. 1.33 x 10^-15 J
B. 2.98 x 10^-27 J
C. 6.63 x 10^-34 J
D. 4.42 x 10^-19 J
Answer: D
Conceptual Explanation: Energy is calculated using E = hc/λ. E = (6.626 x 10^-34 J·s *
3.00 x 10^8 m/s) / (450 x 10^-9 m) = 4.42 x 10^-19 J.
2. Which of the following sets of quantum numbers (n, l, ml, ms) is NOT allowed?
A. 3, 2, -2, +1/2
B. 1, 1, 0, +1/2
C. 3, 0, 0, +1/2
D. 2, 1, 0, -1/2
,Answer: B
Conceptual Explanation: For n=1, the only possible value for l is 0. If n=1, l cannot be 1
because l must be less than n.
3. What is the correct ground-state electron configuration for the Copper (Cu) atom?
A. [Ar] 4s2 3d9
B. [Kr] 4s1 3d10
C. [Ar] 4s2 3d10
D. [Ar] 4s1 3d10
Answer: D
Conceptual Explanation: Copper is an exception to the Aufbau principle; it promotes one
4s electron to the 3d subshell to achieve a full 3d10 stability.
4. Which element has the highest first ionization energy?
A. Nitrogen
B. Helium
C. Fluorine
D. Oxygen
Answer: B
, Conceptual Explanation: Helium has the highest first ionization energy of all elements
due to its small radius and full valence shell.
5. The de Broglie wavelength of a particle is inversely proportional to its:
A. Charge
B. Potential energy
C. Momentum
D. Spin
Answer: C
Conceptual Explanation: The de Broglie equation is λ = h/p, where p is momentum (mass
times velocity).
6. In the photoelectric effect, if the frequency of the incident light is below the threshold
frequency:
A. Electrons are emitted with low kinetic energy
B. Electrons are emitted after a long delay
C. No electrons are emitted regardless of intensity
D. Only a few electrons are emitted
Answer: C
Conceptual Explanation: Photoemission only occurs if the photon energy (hν) exceeds the
work function. Intensity only increases the count if the threshold is met.
