Department of Chemistry
012 • 3–2 HC
CH College of Natural Sciences & Mathematics
VERITAS ET SCIENTIA
EST. 1869
CHEM 210 — Exam 1
C H A PT E R S 2 – 3 : ATO M I C ST R U C T U R E , Q U A N T U M T H E O R Y & C H E M I C A L B O N D I N G
INSTITUTION Department of Chemistry EXAM CODE CHEM-210-EX1C-2026
PROGRAM CHEM 210 — General Chemistry ACADEMIC YEAR
EXAM TITLE Exam 1 (Chapters 2–3) — Atoms, Elements TOTAL QUESTIONS 30 Questions
& Periodicity
COURSE TITLE General Chemistry I FORMAT Multiple Choice / True-False — Select the
Single Best Answer
EXAMINATION INSTRUCTIONS
▸ Select the single best answer for each question.
▸ Questions cover atomic structure (protons, neutrons, electrons), isotopes, periodic table organization, electromagnetic
spectrum, quantum numbers, electron configuration, orbital diagrams, periodic trends, and chemical bonding fundamentals.
▸ Distinguish carefully between related concepts such as cations vs. anions, emission vs. absorption, paramagnetic vs.
diamagnetic, and the four quantum numbers.
▸ Correct answers and detailed rationales appear below each question for comprehensive review.
▸ All content is derived from CHEM 210 Chapters 2–3 curriculum.
SECTION I — ATOMS, QUANTUM THEORY & PERIODIC TRENDS Questions 1 – 30
1. An atom is best defined as:
A. A combination of two or more elements in a fixed ratio
B. The smallest building blocks of matter
C. A group of molecules bonded together
D. A positively charged particle only
CORRECT ANSWER B — The smallest building blocks of matter
RATIONALE An atom is the fundamental unit of an element — the smallest particle that retains the chemical identity of
that element. It consists of a nucleus (protons + neutrons) surrounded by electrons. Option A describes a
compound; Option C describes a molecular aggregate. Atoms are the basic building blocks from which all
matter is constructed.
, 2. The atomic number (Z) equals the number of:
A. Neutrons in the nucleus
B. Protons in the nucleus
C. Electrons in a neutral atom
D. Both B and C — protons and electrons are equal in a neutral atom
CORRECT ANSWER D — Both B and C — protons and electrons are equal in a neutral atom
RATIONALE The atomic number (Z) is the number of protons in the nucleus — this defines the element. In a neutral atom,
the number of electrons equals the number of protons (Z). The mass number (A) = protons + neutrons. The
number of neutrons = A – Z. Z determines the element's identity and position on the periodic table.
3. The mass number (A) equals the number of:
A. Protons only
B. Electrons only
C. Protons and neutrons in the nucleus
D. Protons and electrons combined
CORRECT ANSWER C — Protons and neutrons in the nucleus
RATIONALE Mass number A = Z (protons) + N (neutrons). It is always an integer representing the total number of nucleons.
Isotopes have the same Z but different A (different neutron counts). For example, carbon-12 has 6 protons + 6
neutrons (A = 12), while carbon-14 has 6 protons + 8 neutrons (A = 14).
4. The number of neutrons in an atom can be calculated as:
A. Atomic number minus mass number
B. Mass number minus atomic number
C. Atomic number plus mass number
D. Mass number divided by atomic number
CORRECT ANSWER B — Mass number minus atomic number
RATIONALE Neutrons (N) = A – Z. Since mass number = protons + neutrons, subtracting the proton count (Z) yields the
neutron count. For chlorine-35: N = 35 – 17 = 18 neutrons. For chlorine-37: N = 37 – 17 = 20 neutrons. These
two chlorine isotopes have identical chemical properties but different masses.
5. Anions are:
A. Positively charged atoms formed when an atom loses electrons
B. Neutral atoms with equal protons and electrons
C. Negatively charged atoms formed when an atom gains one or more electrons
D. Atoms with extra neutrons in the nucleus
CORRECT ANSWER C — Negatively charged atoms formed when an atom gains one or more electrons
RATIONALE Anions form when a neutral atom accepts extra electrons, giving it a net negative charge. Nonmetals typically
form anions (e.g., Cl gains 1 electron → Cl⁻; O gains 2 electrons → O²⁻). Option A describes cations. Anions are
larger than their parent atoms because added electrons increase electron-electron repulsion, expanding the
electron cloud.
012 • 3–2 HC
CH College of Natural Sciences & Mathematics
VERITAS ET SCIENTIA
EST. 1869
CHEM 210 — Exam 1
C H A PT E R S 2 – 3 : ATO M I C ST R U C T U R E , Q U A N T U M T H E O R Y & C H E M I C A L B O N D I N G
INSTITUTION Department of Chemistry EXAM CODE CHEM-210-EX1C-2026
PROGRAM CHEM 210 — General Chemistry ACADEMIC YEAR
EXAM TITLE Exam 1 (Chapters 2–3) — Atoms, Elements TOTAL QUESTIONS 30 Questions
& Periodicity
COURSE TITLE General Chemistry I FORMAT Multiple Choice / True-False — Select the
Single Best Answer
EXAMINATION INSTRUCTIONS
▸ Select the single best answer for each question.
▸ Questions cover atomic structure (protons, neutrons, electrons), isotopes, periodic table organization, electromagnetic
spectrum, quantum numbers, electron configuration, orbital diagrams, periodic trends, and chemical bonding fundamentals.
▸ Distinguish carefully between related concepts such as cations vs. anions, emission vs. absorption, paramagnetic vs.
diamagnetic, and the four quantum numbers.
▸ Correct answers and detailed rationales appear below each question for comprehensive review.
▸ All content is derived from CHEM 210 Chapters 2–3 curriculum.
SECTION I — ATOMS, QUANTUM THEORY & PERIODIC TRENDS Questions 1 – 30
1. An atom is best defined as:
A. A combination of two or more elements in a fixed ratio
B. The smallest building blocks of matter
C. A group of molecules bonded together
D. A positively charged particle only
CORRECT ANSWER B — The smallest building blocks of matter
RATIONALE An atom is the fundamental unit of an element — the smallest particle that retains the chemical identity of
that element. It consists of a nucleus (protons + neutrons) surrounded by electrons. Option A describes a
compound; Option C describes a molecular aggregate. Atoms are the basic building blocks from which all
matter is constructed.
, 2. The atomic number (Z) equals the number of:
A. Neutrons in the nucleus
B. Protons in the nucleus
C. Electrons in a neutral atom
D. Both B and C — protons and electrons are equal in a neutral atom
CORRECT ANSWER D — Both B and C — protons and electrons are equal in a neutral atom
RATIONALE The atomic number (Z) is the number of protons in the nucleus — this defines the element. In a neutral atom,
the number of electrons equals the number of protons (Z). The mass number (A) = protons + neutrons. The
number of neutrons = A – Z. Z determines the element's identity and position on the periodic table.
3. The mass number (A) equals the number of:
A. Protons only
B. Electrons only
C. Protons and neutrons in the nucleus
D. Protons and electrons combined
CORRECT ANSWER C — Protons and neutrons in the nucleus
RATIONALE Mass number A = Z (protons) + N (neutrons). It is always an integer representing the total number of nucleons.
Isotopes have the same Z but different A (different neutron counts). For example, carbon-12 has 6 protons + 6
neutrons (A = 12), while carbon-14 has 6 protons + 8 neutrons (A = 14).
4. The number of neutrons in an atom can be calculated as:
A. Atomic number minus mass number
B. Mass number minus atomic number
C. Atomic number plus mass number
D. Mass number divided by atomic number
CORRECT ANSWER B — Mass number minus atomic number
RATIONALE Neutrons (N) = A – Z. Since mass number = protons + neutrons, subtracting the proton count (Z) yields the
neutron count. For chlorine-35: N = 35 – 17 = 18 neutrons. For chlorine-37: N = 37 – 17 = 20 neutrons. These
two chlorine isotopes have identical chemical properties but different masses.
5. Anions are:
A. Positively charged atoms formed when an atom loses electrons
B. Neutral atoms with equal protons and electrons
C. Negatively charged atoms formed when an atom gains one or more electrons
D. Atoms with extra neutrons in the nucleus
CORRECT ANSWER C — Negatively charged atoms formed when an atom gains one or more electrons
RATIONALE Anions form when a neutral atom accepts extra electrons, giving it a net negative charge. Nonmetals typically
form anions (e.g., Cl gains 1 electron → Cl⁻; O gains 2 electrons → O²⁻). Option A describes cations. Anions are
larger than their parent atoms because added electrons increase electron-electron repulsion, expanding the
electron cloud.
