1
CHEM 210 - MIDTERM EXAM 2026/2027 | 50
VERIFIED Q&A | DETAILED RATIONALES | NGN-
ALIGNED | PASS GUARANTEED – A+ GRADED
SECTION I: ATOMIC STRUCTURE AND PERIODIC TRENDS - Questions 1-10
Q1: Atomic number
The student is reviewing atomic structure. What does the atomic number of an element
represent?
A. Number of neutrons
B. Number of protons
C. Number of electrons
D. Mass number
Correct Answer: B
Rationale: The atomic number (Z) equals the number of protons in the nucleus. It defines the
element’s identity. In a neutral atom, electrons equal protons, but the atomic number itself
refers only to protons. [100% CORRECT]
Q2: Isotopes
The student is reviewing isotopes. What are isotopes?
A. Atoms of the same element with different numbers of protons
B. Atoms of the same element with different numbers of neutrons
C. Atoms with different numbers of electrons
D. Ions with a positive charge
Correct Answer: B
Rationale: Isotopes are atoms of the same element that have the same number of protons but
different numbers of neutrons, resulting in different mass numbers. [100% CORRECT]
Q3: Electron configuration
The student is reviewing electron configuration. What is the electron configuration of oxygen (Z
= 8)?
A. 1s² 2s² 2p⁴
B. 1s² 2s² 2p⁶
C. 1s² 2s² 2p³
D. 1s² 2s² 2p⁵
, 2
Correct Answer: A
Rationale: Oxygen has 8 electrons: 2 in 1s, 2 in 2s, and 4 in 2p. Therefore, 1s² 2s² 2p⁴. [100%
CORRECT]
Q4: Periodic trend: atomic radius
The student is reviewing periodic trends. How does atomic radius change across a period from
left to right?
A. Increases
B. Decreases
C. Remains constant
D. Increases then decreases
Correct Answer: B
Rationale: Across a period, increasing nuclear charge pulls electrons closer, so atomic radius
generally decreases from left to right. Down a group, radius increases due to additional electron
shells. [100% CORRECT]
Q5: Periodic trend: ionization energy
The student is reviewing periodic trends. How does first ionization energy change down a
group?
A. Increases
B. Decreases
C. Remains constant
D. Randomly fluctuates
Correct Answer: B
Rationale: Down a group, valence electrons are farther from the nucleus and shielded by inner
electrons, so ionization energy decreases. Across a period, it generally increases. [100%
CORRECT]
Q6: Electronegativity
The student is reviewing electronegativity. Which element has the highest electronegativity?
A. Fluorine
B. Oxygen
C. Chlorine
D. Nitrogen
Correct Answer: A
Rationale: Fluorine is the most electronegative element (Pauling scale ~4.0). Electronegativity
increases across a period and decreases down a group. [100% CORRECT]
CHEM 210 - MIDTERM EXAM 2026/2027 | 50
VERIFIED Q&A | DETAILED RATIONALES | NGN-
ALIGNED | PASS GUARANTEED – A+ GRADED
SECTION I: ATOMIC STRUCTURE AND PERIODIC TRENDS - Questions 1-10
Q1: Atomic number
The student is reviewing atomic structure. What does the atomic number of an element
represent?
A. Number of neutrons
B. Number of protons
C. Number of electrons
D. Mass number
Correct Answer: B
Rationale: The atomic number (Z) equals the number of protons in the nucleus. It defines the
element’s identity. In a neutral atom, electrons equal protons, but the atomic number itself
refers only to protons. [100% CORRECT]
Q2: Isotopes
The student is reviewing isotopes. What are isotopes?
A. Atoms of the same element with different numbers of protons
B. Atoms of the same element with different numbers of neutrons
C. Atoms with different numbers of electrons
D. Ions with a positive charge
Correct Answer: B
Rationale: Isotopes are atoms of the same element that have the same number of protons but
different numbers of neutrons, resulting in different mass numbers. [100% CORRECT]
Q3: Electron configuration
The student is reviewing electron configuration. What is the electron configuration of oxygen (Z
= 8)?
A. 1s² 2s² 2p⁴
B. 1s² 2s² 2p⁶
C. 1s² 2s² 2p³
D. 1s² 2s² 2p⁵
, 2
Correct Answer: A
Rationale: Oxygen has 8 electrons: 2 in 1s, 2 in 2s, and 4 in 2p. Therefore, 1s² 2s² 2p⁴. [100%
CORRECT]
Q4: Periodic trend: atomic radius
The student is reviewing periodic trends. How does atomic radius change across a period from
left to right?
A. Increases
B. Decreases
C. Remains constant
D. Increases then decreases
Correct Answer: B
Rationale: Across a period, increasing nuclear charge pulls electrons closer, so atomic radius
generally decreases from left to right. Down a group, radius increases due to additional electron
shells. [100% CORRECT]
Q5: Periodic trend: ionization energy
The student is reviewing periodic trends. How does first ionization energy change down a
group?
A. Increases
B. Decreases
C. Remains constant
D. Randomly fluctuates
Correct Answer: B
Rationale: Down a group, valence electrons are farther from the nucleus and shielded by inner
electrons, so ionization energy decreases. Across a period, it generally increases. [100%
CORRECT]
Q6: Electronegativity
The student is reviewing electronegativity. Which element has the highest electronegativity?
A. Fluorine
B. Oxygen
C. Chlorine
D. Nitrogen
Correct Answer: A
Rationale: Fluorine is the most electronegative element (Pauling scale ~4.0). Electronegativity
increases across a period and decreases down a group. [100% CORRECT]
