1 MAXE · 401 MEHC
★ ★
University Chemistry Department
College of Arts & Sciences
UNIVERSITY
LUX ET VERITAS
chem 104 exam 1
G E N E RA L C H E M I ST RY — F I RST E X A M I N AT I O N
INSTITUTION [UNVERIFIED] University PROGRAM Undergraduate — General
Chemistry Department Chemistry
COURSE CODE CHEM 104 COURSE TITLE General Chemistry I
ACADEMIC YEAR EXAM TITLE chem 104 exam 1
TOTAL QUESTIONS 29 Questions FORMAT Multiple Choice — Select the
Single Best Answer
EXAMINATION INSTRUCTIONS
▸ Select the single best answer for each question unless otherwise instructed.
▸ All calculations should be performed with proper significant figures as specified.
▸ Periodic table knowledge and fundamental chemistry principles are testable content.
▸ Correct answers and detailed rationales appear below each question for study purposes.
▸ All content is derived directly from the CHEM 104 course material.
, SECTION I — MATTER, MEASUREMENT, ATOMIC
Questions 1 – 29
STRUCTURE & BONDING
1. How many valence electrons would be found in the correct Lewis dot structure of C₂H₆?
A. 10
B. 12
C. 14
D. 16
CORRECT ANSWER C — 14
RATIONALE Ethane (C₂H₆) contains two carbon atoms (each with 4 valence electrons = 8) and
six hydrogen atoms (each with 1 valence electron = 6). The total is 8 + 6 = 14
valence electrons. In the Lewis structure, these are distributed as C–C and C–H
single bonds with each carbon achieving an octet.
2. Two isotopes of the same element will have the same mass number.
A. True, isotopes always have identical mass numbers
B. False, they have the same number of protons but different number of neutrons which
changes their mass number
C. True, mass number is determined only by protons
D. False, isotopes have different numbers of protons
CORRECT ANSWER B — False, they have the same number of protons but different number of
neutrons which changes their mass number
RATIONALE Isotopes of the same element have the same atomic number (number of protons)
but different numbers of neutrons. Since mass number = protons + neutrons,
different neutron counts produce different mass numbers. For example, carbon-
12 (6 protons + 6 neutrons) and carbon-14 (6 protons + 8 neutrons) are isotopes
with mass numbers 12 and 14 respectively.
, 3. Which of the following numbers contains 5 significant figures?
A. 0.0049
B. 4910
C. 4.9100
D. 49100
CORRECT ANSWER C — 4.9100
RATIONALE The number 4.9100 contains 5 significant figures: the 4, 9, 1, and both trailing
zeros after the decimal point. Trailing zeros after a decimal point are always
significant. 0.0049 has 2 sig figs (leading zeros are not significant). 4910 has 3 sig
figs unless written with a decimal point. 49100 has 3 sig figs (trailing zeros without
a decimal are not significant).
4. How many single bonds does an atom of carbon normally make in a covalent molecule if
there are no double or triple bonds?
A. 2
B. 3
C. 4
D. 6
CORRECT ANSWER C—4
RATIONALE Carbon has 4 valence electrons and needs 4 more to achieve an octet (8
electrons). In covalent bonding, carbon shares its 4 valence electrons by forming 4
single bonds (or equivalent combinations of single, double, and triple bonds).
This is why carbon forms four bonds in molecules like methane (CH₄) where it
makes four C–H single bonds.
★ ★
University Chemistry Department
College of Arts & Sciences
UNIVERSITY
LUX ET VERITAS
chem 104 exam 1
G E N E RA L C H E M I ST RY — F I RST E X A M I N AT I O N
INSTITUTION [UNVERIFIED] University PROGRAM Undergraduate — General
Chemistry Department Chemistry
COURSE CODE CHEM 104 COURSE TITLE General Chemistry I
ACADEMIC YEAR EXAM TITLE chem 104 exam 1
TOTAL QUESTIONS 29 Questions FORMAT Multiple Choice — Select the
Single Best Answer
EXAMINATION INSTRUCTIONS
▸ Select the single best answer for each question unless otherwise instructed.
▸ All calculations should be performed with proper significant figures as specified.
▸ Periodic table knowledge and fundamental chemistry principles are testable content.
▸ Correct answers and detailed rationales appear below each question for study purposes.
▸ All content is derived directly from the CHEM 104 course material.
, SECTION I — MATTER, MEASUREMENT, ATOMIC
Questions 1 – 29
STRUCTURE & BONDING
1. How many valence electrons would be found in the correct Lewis dot structure of C₂H₆?
A. 10
B. 12
C. 14
D. 16
CORRECT ANSWER C — 14
RATIONALE Ethane (C₂H₆) contains two carbon atoms (each with 4 valence electrons = 8) and
six hydrogen atoms (each with 1 valence electron = 6). The total is 8 + 6 = 14
valence electrons. In the Lewis structure, these are distributed as C–C and C–H
single bonds with each carbon achieving an octet.
2. Two isotopes of the same element will have the same mass number.
A. True, isotopes always have identical mass numbers
B. False, they have the same number of protons but different number of neutrons which
changes their mass number
C. True, mass number is determined only by protons
D. False, isotopes have different numbers of protons
CORRECT ANSWER B — False, they have the same number of protons but different number of
neutrons which changes their mass number
RATIONALE Isotopes of the same element have the same atomic number (number of protons)
but different numbers of neutrons. Since mass number = protons + neutrons,
different neutron counts produce different mass numbers. For example, carbon-
12 (6 protons + 6 neutrons) and carbon-14 (6 protons + 8 neutrons) are isotopes
with mass numbers 12 and 14 respectively.
, 3. Which of the following numbers contains 5 significant figures?
A. 0.0049
B. 4910
C. 4.9100
D. 49100
CORRECT ANSWER C — 4.9100
RATIONALE The number 4.9100 contains 5 significant figures: the 4, 9, 1, and both trailing
zeros after the decimal point. Trailing zeros after a decimal point are always
significant. 0.0049 has 2 sig figs (leading zeros are not significant). 4910 has 3 sig
figs unless written with a decimal point. 49100 has 3 sig figs (trailing zeros without
a decimal are not significant).
4. How many single bonds does an atom of carbon normally make in a covalent molecule if
there are no double or triple bonds?
A. 2
B. 3
C. 4
D. 6
CORRECT ANSWER C—4
RATIONALE Carbon has 4 valence electrons and needs 4 more to achieve an octet (8
electrons). In covalent bonding, carbon shares its 4 valence electrons by forming 4
single bonds (or equivalent combinations of single, double, and triple bonds).
This is why carbon forms four bonds in molecules like methane (CH₄) where it
makes four C–H single bonds.
