CHEM 103 FINAL EXAM | ALL QUESTIONS AND
ANSWERS | A+ GRADED | COMPREHENSIVE
EXAM GUIDE 2026/2027
1. Which statement best describes the role of electrons in the formation of a chemical
bond?
A. Electrons determine the number of neutrons in an atom
B. Electrons are transferred or shared to achieve greater stability
C. Electrons determine the atomic mass only
D. Electrons are located exclusively inside the nucleus
Answer: B
Rationale: Atoms form chemical bonds primarily by transferring or sharing valence electrons to
reach a more stable electron configuration.
2. An atom has 17 protons, 18 neutrons, and 17 electrons. What are its atomic number and
mass number, respectively?
A. 17 and 35
B. 18 and 35
C. 17 and 34
D. 35 and 17
Answer: A
Rationale: Atomic number equals the number of protons, while mass number equals protons
plus neutrons: 17 + 18 = 35.
3. A student is asked to identify the element represented by the electron configuration
1s²2s²2p⁶3s¹. Which element should be selected?
A. Magnesium
B. Neon
C. Sodium
D. Aluminum
Answer: C
Rationale: The configuration contains 11 electrons, corresponding to sodium (Na).
,4. Which periodic trend generally increases from left to right across a period?
A. Atomic radius
B. Metallic character
C. Effective nuclear charge
D. Number of occupied energy levels
Answer: C
Rationale: Effective nuclear charge generally increases across a period because proton number
increases while shielding changes relatively little.
5. Which element would be expected to have the largest atomic radius?
A. Li
B. Na
C. K
D. Rb
Answer: D
Rationale: Atomic radius increases down a group because additional electron shells place the
valence electrons farther from the nucleus.
6. A neutral atom contains 12 protons. What is the most likely charge of the ion it forms
when it loses two electrons?
A. 2−
B. 1−
C. 1+
D. 2+
Answer: D
Rationale: Losing two negatively charged electrons leaves the atom with two more positive
charges than negative charges, producing a 2+ ion.
7. Which compound contains predominantly ionic bonding?
A. CO₂
B. NaCl
, C. CH₄
D. SO₂
Answer: B
Rationale: Sodium is a metal and chlorine is a nonmetal, so NaCl forms through electron
transfer and ionic attraction.
8. Which molecular geometry is associated with a carbon atom having four bonding
electron pairs and no lone pairs?
A. Linear
B. Bent
C. Trigonal planar
D. Tetrahedral
Answer: D
Rationale: Four electron domains around a central atom with no lone pairs produce a
tetrahedral molecular geometry.
9. Which molecule is expected to have a linear molecular geometry?
A. CO₂
B. H₂O
C. NH₃
D. CH₄
Answer: A
Rationale: Carbon dioxide has two electron domains around carbon and no lone pairs on the
central atom, giving a linear structure.
10. Which intermolecular force is particularly important between molecules containing O–
H bonds?
A. London dispersion only
B. Hydrogen bonding
C. Metallic bonding
D. Ionic bonding
Answer: B
, Rationale: Hydrogen bonded to highly electronegative atoms such as oxygen allows strong
hydrogen-bond interactions between molecules.
11. A laboratory sample contains 0.50 mol of NaCl. Approximately how many formula
units does it contain?
A. 3.01 × 10²³
B. 6.02 × 10²³
C. 1.20 × 10²⁴
D. 0.50 × 10²³
Answer: A
Rationale: One mole contains 6.022 × 10²³ particles, so 0.50 mol contains approximately 3.01 ×
10²³ formula units.
12. What is the molar mass of H₂O?
A. 16.00 g/mol
B. 17.00 g/mol
C. 18.02 g/mol
D. 20.02 g/mol
Answer: C
Rationale: Water contains two hydrogen atoms and one oxygen atom: 2(1.008) + 16.00 ≈ 18.02
g/mol.
13. A compound contains 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen by mass.
What is its empirical formula?
A. CHO
B. CH₂O
C. C₂H₄O₂
D. C₂HO
Answer: B
Rationale: Converting the percentages to mole ratios gives approximately 1:2:1, resulting in
CH₂O.
ANSWERS | A+ GRADED | COMPREHENSIVE
EXAM GUIDE 2026/2027
1. Which statement best describes the role of electrons in the formation of a chemical
bond?
A. Electrons determine the number of neutrons in an atom
B. Electrons are transferred or shared to achieve greater stability
C. Electrons determine the atomic mass only
D. Electrons are located exclusively inside the nucleus
Answer: B
Rationale: Atoms form chemical bonds primarily by transferring or sharing valence electrons to
reach a more stable electron configuration.
2. An atom has 17 protons, 18 neutrons, and 17 electrons. What are its atomic number and
mass number, respectively?
A. 17 and 35
B. 18 and 35
C. 17 and 34
D. 35 and 17
Answer: A
Rationale: Atomic number equals the number of protons, while mass number equals protons
plus neutrons: 17 + 18 = 35.
3. A student is asked to identify the element represented by the electron configuration
1s²2s²2p⁶3s¹. Which element should be selected?
A. Magnesium
B. Neon
C. Sodium
D. Aluminum
Answer: C
Rationale: The configuration contains 11 electrons, corresponding to sodium (Na).
,4. Which periodic trend generally increases from left to right across a period?
A. Atomic radius
B. Metallic character
C. Effective nuclear charge
D. Number of occupied energy levels
Answer: C
Rationale: Effective nuclear charge generally increases across a period because proton number
increases while shielding changes relatively little.
5. Which element would be expected to have the largest atomic radius?
A. Li
B. Na
C. K
D. Rb
Answer: D
Rationale: Atomic radius increases down a group because additional electron shells place the
valence electrons farther from the nucleus.
6. A neutral atom contains 12 protons. What is the most likely charge of the ion it forms
when it loses two electrons?
A. 2−
B. 1−
C. 1+
D. 2+
Answer: D
Rationale: Losing two negatively charged electrons leaves the atom with two more positive
charges than negative charges, producing a 2+ ion.
7. Which compound contains predominantly ionic bonding?
A. CO₂
B. NaCl
, C. CH₄
D. SO₂
Answer: B
Rationale: Sodium is a metal and chlorine is a nonmetal, so NaCl forms through electron
transfer and ionic attraction.
8. Which molecular geometry is associated with a carbon atom having four bonding
electron pairs and no lone pairs?
A. Linear
B. Bent
C. Trigonal planar
D. Tetrahedral
Answer: D
Rationale: Four electron domains around a central atom with no lone pairs produce a
tetrahedral molecular geometry.
9. Which molecule is expected to have a linear molecular geometry?
A. CO₂
B. H₂O
C. NH₃
D. CH₄
Answer: A
Rationale: Carbon dioxide has two electron domains around carbon and no lone pairs on the
central atom, giving a linear structure.
10. Which intermolecular force is particularly important between molecules containing O–
H bonds?
A. London dispersion only
B. Hydrogen bonding
C. Metallic bonding
D. Ionic bonding
Answer: B
, Rationale: Hydrogen bonded to highly electronegative atoms such as oxygen allows strong
hydrogen-bond interactions between molecules.
11. A laboratory sample contains 0.50 mol of NaCl. Approximately how many formula
units does it contain?
A. 3.01 × 10²³
B. 6.02 × 10²³
C. 1.20 × 10²⁴
D. 0.50 × 10²³
Answer: A
Rationale: One mole contains 6.022 × 10²³ particles, so 0.50 mol contains approximately 3.01 ×
10²³ formula units.
12. What is the molar mass of H₂O?
A. 16.00 g/mol
B. 17.00 g/mol
C. 18.02 g/mol
D. 20.02 g/mol
Answer: C
Rationale: Water contains two hydrogen atoms and one oxygen atom: 2(1.008) + 16.00 ≈ 18.02
g/mol.
13. A compound contains 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen by mass.
What is its empirical formula?
A. CHO
B. CH₂O
C. C₂H₄O₂
D. C₂HO
Answer: B
Rationale: Converting the percentages to mole ratios gives approximately 1:2:1, resulting in
CH₂O.
