CHEM 121 MODULE 2: ATOMIC
STRUCTURE AND PERIODIC TABLE
QUESTIONS AND ANSWERS 2026/2027
UPDATE || 100% GUARANTEED PASS
1. According to the Dalton Atomic Theory, which of the following statements is considered
incorrect based on modern scientific understanding?
A. All matter is made of atoms.
B. Compounds are formed by a combination of two or more different kinds of atoms.
C. A chemical reaction is a rearrangement of atoms.
D. All atoms of a given element are identical in mass and properties.
Answer: D
Conceptual Explanation: Dalton’s theory stated all atoms of an element are identical;
however, we now know that isotopes exist, meaning atoms of the same element can have
different masses.
2. What was the primary conclusion of Rutherford’s gold foil experiment?
A. Electrons are located in specific energy levels.
B. Atoms are solid spheres of uniform density.
C. Atoms contain a small, dense, positively charged nucleus.
,D. Neutrons are located in the nucleus with protons.
Answer: C
Conceptual Explanation: Rutherford observed that most alpha particles passed through
the foil, but some were deflected at large angles, indicating a concentrated positive charge
at the center.
3. An isotope of an element has 20 protons, 20 electrons, and 22 neutrons. What is its mass
number?
A. 20
B. 40
C. 62
D. 42
Answer: D
Conceptual Explanation: The mass number is the sum of protons and neutrons (20 + 22 =
42).
4. Which of the following elements is classified as a metalloid?
A. Aluminum
B. Gallium
C. Carbon
D. Silicon
, Answer: D
Conceptual Explanation: Silicon is a well-known metalloid located along the ‘staircase’ of
the periodic table, exhibiting properties of both metals and nonmetals.
5. How many electrons are present in a Cu2+ ion (Atomic Number 29)?
A. 29
B. 27
C. 31
D. 28
Answer: B
Conceptual Explanation: A neutral copper atom has 29 electrons. A 2+ charge indicates
the loss of 2 electrons, resulting in 27 electrons.
6. Which subshell is filled immediately after the 4s subshell according to the Aufbau
principle?
A. 4p
B. 4d
C. 5s
D. 3d
Answer: D
STRUCTURE AND PERIODIC TABLE
QUESTIONS AND ANSWERS 2026/2027
UPDATE || 100% GUARANTEED PASS
1. According to the Dalton Atomic Theory, which of the following statements is considered
incorrect based on modern scientific understanding?
A. All matter is made of atoms.
B. Compounds are formed by a combination of two or more different kinds of atoms.
C. A chemical reaction is a rearrangement of atoms.
D. All atoms of a given element are identical in mass and properties.
Answer: D
Conceptual Explanation: Dalton’s theory stated all atoms of an element are identical;
however, we now know that isotopes exist, meaning atoms of the same element can have
different masses.
2. What was the primary conclusion of Rutherford’s gold foil experiment?
A. Electrons are located in specific energy levels.
B. Atoms are solid spheres of uniform density.
C. Atoms contain a small, dense, positively charged nucleus.
,D. Neutrons are located in the nucleus with protons.
Answer: C
Conceptual Explanation: Rutherford observed that most alpha particles passed through
the foil, but some were deflected at large angles, indicating a concentrated positive charge
at the center.
3. An isotope of an element has 20 protons, 20 electrons, and 22 neutrons. What is its mass
number?
A. 20
B. 40
C. 62
D. 42
Answer: D
Conceptual Explanation: The mass number is the sum of protons and neutrons (20 + 22 =
42).
4. Which of the following elements is classified as a metalloid?
A. Aluminum
B. Gallium
C. Carbon
D. Silicon
, Answer: D
Conceptual Explanation: Silicon is a well-known metalloid located along the ‘staircase’ of
the periodic table, exhibiting properties of both metals and nonmetals.
5. How many electrons are present in a Cu2+ ion (Atomic Number 29)?
A. 29
B. 27
C. 31
D. 28
Answer: B
Conceptual Explanation: A neutral copper atom has 29 electrons. A 2+ charge indicates
the loss of 2 electrons, resulting in 27 electrons.
6. Which subshell is filled immediately after the 4s subshell according to the Aufbau
principle?
A. 4p
B. 4d
C. 5s
D. 3d
Answer: D
