CHEM 121 Module 2 Exam: Atoms, Elements, and Periodic Trends
2026/2027 UPDATE
1. What subatomic particles are located in the nucleus of an atom?
A. Protons and neutrons
B. Protons and electrons
C. Neutrons and electrons
D. Only protons
Answer: A
Rationale: The nucleus contains protons (positive charge) and neutrons (neutral charge),
while electrons orbit the nucleus.
2. The identity of an element is determined by its number of:
A. Neutrons
B. Electrons
C. Valence electrons
D. Protons
Answer: D
Rationale: The atomic number (number of protons) defines which element an atom is.
3. Which of the following is the correct symbol for the element Lead?
A. Ld
B. Le
C. Sn
D. Pb
Answer: D
,Rationale: The symbol for Lead is Pb, derived from the Latin word ‘plumbum’.
4. An atom with 6 protons, 8 neutrons, and 6 electrons has a mass number of:
A. 6
B. 12
C. 20
D. 14
Answer: D
Rationale: Mass number = Protons + Neutrons. 6 + 8 = 14.
5. Which subatomic particle has a negligible mass compared to the others?
A. Proton
B. Neutron
C. Electron
D. Nucleus
Answer: C
Rationale: Electrons are significantly smaller (about 1/1836th of a proton) and their mass
is usually ignored in mass number calculations.
6. Isotopes of the same element have the same number of ____ but different
numbers of ____.
A. Protons; neutrons
B. Neutrons; protons
C. Protons; electrons
D. Electrons; protons
Answer: A
Rationale: Isotopes are atoms of the same element (same protons) with different masses
(different neutrons).
, 7. How many neutrons are in an atom of Carbon-14 (Atomic number 6)?
A. 6
B. 14
C. 8
D. 12
Answer: C
Rationale: Neutrons = Mass Number - Atomic Number. 14 - 6 = 8.
8. Which group of elements is known as the Halogens?
A. Group 1
B. Group 2
C. Group 18
D. Group 17
Answer: D
Rationale: Group 17 elements (F, Cl, Br, I, At) are called Halogens.
9. The average atomic mass of an element is calculated based on:
A. The mass of the most common isotope
B. The sum of protons and neutrons in the nucleus
C. The average number of electrons in the valence shell
D. The weighted average of all naturally occurring isotopes
Answer: D
Rationale: Average atomic mass accounts for both the mass and the relative abundance of
each isotope.
2026/2027 UPDATE
1. What subatomic particles are located in the nucleus of an atom?
A. Protons and neutrons
B. Protons and electrons
C. Neutrons and electrons
D. Only protons
Answer: A
Rationale: The nucleus contains protons (positive charge) and neutrons (neutral charge),
while electrons orbit the nucleus.
2. The identity of an element is determined by its number of:
A. Neutrons
B. Electrons
C. Valence electrons
D. Protons
Answer: D
Rationale: The atomic number (number of protons) defines which element an atom is.
3. Which of the following is the correct symbol for the element Lead?
A. Ld
B. Le
C. Sn
D. Pb
Answer: D
,Rationale: The symbol for Lead is Pb, derived from the Latin word ‘plumbum’.
4. An atom with 6 protons, 8 neutrons, and 6 electrons has a mass number of:
A. 6
B. 12
C. 20
D. 14
Answer: D
Rationale: Mass number = Protons + Neutrons. 6 + 8 = 14.
5. Which subatomic particle has a negligible mass compared to the others?
A. Proton
B. Neutron
C. Electron
D. Nucleus
Answer: C
Rationale: Electrons are significantly smaller (about 1/1836th of a proton) and their mass
is usually ignored in mass number calculations.
6. Isotopes of the same element have the same number of ____ but different
numbers of ____.
A. Protons; neutrons
B. Neutrons; protons
C. Protons; electrons
D. Electrons; protons
Answer: A
Rationale: Isotopes are atoms of the same element (same protons) with different masses
(different neutrons).
, 7. How many neutrons are in an atom of Carbon-14 (Atomic number 6)?
A. 6
B. 14
C. 8
D. 12
Answer: C
Rationale: Neutrons = Mass Number - Atomic Number. 14 - 6 = 8.
8. Which group of elements is known as the Halogens?
A. Group 1
B. Group 2
C. Group 18
D. Group 17
Answer: D
Rationale: Group 17 elements (F, Cl, Br, I, At) are called Halogens.
9. The average atomic mass of an element is calculated based on:
A. The mass of the most common isotope
B. The sum of protons and neutrons in the nucleus
C. The average number of electrons in the valence shell
D. The weighted average of all naturally occurring isotopes
Answer: D
Rationale: Average atomic mass accounts for both the mass and the relative abundance of
each isotope.
