Portage Learning CHEM 103 Module 4 Exam
2025: Verified Questions with Detailed
Explanations
A Comprehensive Study Guide for Success
1. Introduction
This study guide is tailored for the Portage Learning CHEM 103 Module 4 Exam 2025, present-
ing 100 carefully curated questions with accurate answers and comprehensive explanations. It
covers key topics including electron configurations, orbital diagrams, chemical bonding, molecu-
lar geometry, and thermochemistry. The design is simple, professional, and visually distinctive,
using dark royal red for emphasis and subtle boxed environments for clarity. No tables are
included, ensuring a streamlined and focused presentation to optimize exam preparation.
2. Electron Configurations
2.1 Question 1
Write the electron configuration for a neutral calcium (Ca) atom. Answer: 1s2 2s2 2p6 3s2 3p6 4s2
Explanation: Calcium, with atomic number 20, has 20 electrons distributed across orbitals
in order of increasing energy. The Aufbau principle dictates filling as follows: 1s (2 elec-
trons), 2s (2), 2p (6), 3s (2), 3p (6), and 4s (2). The 4s2 electrons are calcium’s valence
electrons, key to its reactivity as an alkaline earth metal forming Ca2+ ions.
2.2 Question 2
What is the electron configuration for a sulfur (S) atom? Answer: 1s2 2s2 2p6 3s2 3p4 Expla-
nation: Sulfur, atomic number 16, has 16 electrons. Subshells are filled sequentially: 1s2
(2 electrons), 2s2 (2), 2p6 (6), 3s2 (2), and 3p4 (4). The 3p4 configuration indicates sulfur
requires two electrons to complete its octet, influencing its bonding in compounds like H2 S
or SO2 .
1
,CHEM 103 Module 4 Exam 2025 2
2.3 Question 3
How many valence electrons does a phosphorus (P) atom have? Answer: 5 Explanation:
Phosphorus, atomic number 15, has the electron configuration 1s2 2s2 2p6 3s2 3p3 . Valence
electrons, located in the outermost shell (n=3), include 3s2 (2 electrons) and 3p3 (3 elec-
trons), totaling 5. These electrons enable phosphorus to form three or five bonds, as seen
in PH3 or PCl5 .
2.4 Question 4
Write the electron configuration for a potassium (K) atom. Answer: 1s2 2s2 2p6 3s2 3p6 4s1
Explanation: Potassium, atomic number 19, has 19 electrons: 1s2 (2), 2s2 (2), 2p6 (6), 3s2
(2), 3p6 (6), and 4s1 (1). The single 4s electron is its valence electron, driving high reactivity
as potassium readily loses it to form K+ ions in ionic compounds.
2.5 Question 5
Determine the number of valence electrons in a silicon (Si) atom. Answer: 4 Explanation:
Silicon, atomic number 14, has the configuration 1s2 2s2 2p6 3s2 3p2 . Valence electrons in the
n=3 shell are 3s2 (2) and 3p2 (2), totaling 4. These electrons allow silicon to form four
covalent bonds, critical for compounds like SiH4 and its role in semiconductors.
2.6 Question 6
What is the electron configuration for a chlorine (Cl) atom? Answer: 1s2 2s2 2p6 3s2 3p5
Explanation: Chlorine, atomic number 17, has 17 electrons: 1s2 (2), 2s2 (2), 2p6 (6), 3s2
(2), and 3p5 (5). The 3p5 subshell indicates chlorine is one electron short of an octet,
explaining its tendency to gain an electron in reactions, forming Cl− ions in compounds like
NaCl.
2.7 Question 7
Write the electron configuration for a magnesium (Mg) atom. Answer: 1s2 2s2 2p6 3s2 Expla-
nation: Magnesium, atomic number 12, has 12 electrons: 1s2 (2), 2s2 (2), 2p6 (6), and 3s2
(2). The 3s2 electrons are valence electrons, which magnesium loses to form Mg2+ ions, as
seen in ionic compounds like MgO.
2.8 Question 8
How many valence electrons does an oxygen (O) atom have? Answer: 6 Explanation:
Oxygen, atomic number 8, has the configuration 1s2 2s2 2p4 . Valence electrons in the n=2
shell include 2s2 (2) and 2p4 (4), totaling 6. These electrons enable oxygen to form two
covalent bonds, as in H2 O, or gain two electrons to achieve a stable octet.
Prepared for 2025 Exam
, CHEM 103 Module 4 Exam 2025 3
2.9 Question 9
What is the electron configuration for a sodium (Na) atom? Answer: 1s2 2s2 2p6 3s1 Expla-
nation: Sodium, atomic number 11, has 11 electrons: 1s2 (2), 2s2 (2), 2p6 (6), and 3s1 (1).
The single 3s electron is highly reactive, driving sodium to lose it and form Na+ ions in
compounds like NaCl.
2.10 Question 10
Write the electron configuration for an aluminum (Al) atom. Answer: 1s2 2s2 2p6 3s2 3p1
Explanation: Aluminum, atomic number 13, has 13 electrons: 1s2 (2), 2s2 (2), 2p6 (6), 3s2
(2), and 3p1 (1). The 3s2 3p1 electrons are valence electrons, enabling aluminum to form
three bonds or lose three electrons to form Al3+ .
3. Orbital Diagrams
3.1 Question 11
Draw the orbital diagram for a nitrogen (N) atom. Answer: 1s2 ↑↓ 2s2 ↑↓ 2p3 ↑↑↑ Explana-
tion: Nitrogen, atomic number 7, has the configuration 1s2 2s2 2p3 . The 1s and 2s orbitals
are filled with paired electrons (opposite spins). The 2p subshell has three orbitals, each
occupied by one unpaired electron per Hund’s rule, which favors parallel spins to minimize
repulsion, resulting in ↑↑↑.
3.2 Question 12
Provide the orbital diagram for a carbon (C) atom. Answer: 1s2 ↑↓ 2s2 ↑↓ 2p2 ↑↑ Expla-
nation: Carbon, atomic number 6, has the configuration 1s2 2s2 2p2 . The 1s and 2s orbitals
are paired. The 2p subshell has two electrons in separate orbitals with parallel spins (↑↑)
per Hund’s rule, enabling carbon to form four bonds through hybridization.
3.3 Question 13
What is the orbital diagram for a fluorine (F) atom? Answer: 1s2 ↑↓ 2s2 ↑↓ 2p5 ↑↓↑↓↑
Explanation: Fluorine, atomic number 9, has the configuration 1s2 2s2 2p5 . The 1s and 2s
orbitals are paired. The 2p subshell has three orbitals: two with paired electrons (↑↓) and
one with a single electron (↑), reflecting fluorine’s high reactivity as it seeks one electron for
a stable octet.
3.4 Question 14
Draw the orbital diagram for a boron (B) atom. Answer: 1s2 ↑↓ 2s2 ↑↓ 2p1 ↑ Explanation:
Boron, atomic number 5, has the configuration 1s2 2s2 2p1 . The 1s and 2s orbitals are paired,
while the 2p subshell has one electron in a single orbital (↑), enabling boron to form three
bonds, as in BF3 .
Prepared for 2025 Exam
2025: Verified Questions with Detailed
Explanations
A Comprehensive Study Guide for Success
1. Introduction
This study guide is tailored for the Portage Learning CHEM 103 Module 4 Exam 2025, present-
ing 100 carefully curated questions with accurate answers and comprehensive explanations. It
covers key topics including electron configurations, orbital diagrams, chemical bonding, molecu-
lar geometry, and thermochemistry. The design is simple, professional, and visually distinctive,
using dark royal red for emphasis and subtle boxed environments for clarity. No tables are
included, ensuring a streamlined and focused presentation to optimize exam preparation.
2. Electron Configurations
2.1 Question 1
Write the electron configuration for a neutral calcium (Ca) atom. Answer: 1s2 2s2 2p6 3s2 3p6 4s2
Explanation: Calcium, with atomic number 20, has 20 electrons distributed across orbitals
in order of increasing energy. The Aufbau principle dictates filling as follows: 1s (2 elec-
trons), 2s (2), 2p (6), 3s (2), 3p (6), and 4s (2). The 4s2 electrons are calcium’s valence
electrons, key to its reactivity as an alkaline earth metal forming Ca2+ ions.
2.2 Question 2
What is the electron configuration for a sulfur (S) atom? Answer: 1s2 2s2 2p6 3s2 3p4 Expla-
nation: Sulfur, atomic number 16, has 16 electrons. Subshells are filled sequentially: 1s2
(2 electrons), 2s2 (2), 2p6 (6), 3s2 (2), and 3p4 (4). The 3p4 configuration indicates sulfur
requires two electrons to complete its octet, influencing its bonding in compounds like H2 S
or SO2 .
1
,CHEM 103 Module 4 Exam 2025 2
2.3 Question 3
How many valence electrons does a phosphorus (P) atom have? Answer: 5 Explanation:
Phosphorus, atomic number 15, has the electron configuration 1s2 2s2 2p6 3s2 3p3 . Valence
electrons, located in the outermost shell (n=3), include 3s2 (2 electrons) and 3p3 (3 elec-
trons), totaling 5. These electrons enable phosphorus to form three or five bonds, as seen
in PH3 or PCl5 .
2.4 Question 4
Write the electron configuration for a potassium (K) atom. Answer: 1s2 2s2 2p6 3s2 3p6 4s1
Explanation: Potassium, atomic number 19, has 19 electrons: 1s2 (2), 2s2 (2), 2p6 (6), 3s2
(2), 3p6 (6), and 4s1 (1). The single 4s electron is its valence electron, driving high reactivity
as potassium readily loses it to form K+ ions in ionic compounds.
2.5 Question 5
Determine the number of valence electrons in a silicon (Si) atom. Answer: 4 Explanation:
Silicon, atomic number 14, has the configuration 1s2 2s2 2p6 3s2 3p2 . Valence electrons in the
n=3 shell are 3s2 (2) and 3p2 (2), totaling 4. These electrons allow silicon to form four
covalent bonds, critical for compounds like SiH4 and its role in semiconductors.
2.6 Question 6
What is the electron configuration for a chlorine (Cl) atom? Answer: 1s2 2s2 2p6 3s2 3p5
Explanation: Chlorine, atomic number 17, has 17 electrons: 1s2 (2), 2s2 (2), 2p6 (6), 3s2
(2), and 3p5 (5). The 3p5 subshell indicates chlorine is one electron short of an octet,
explaining its tendency to gain an electron in reactions, forming Cl− ions in compounds like
NaCl.
2.7 Question 7
Write the electron configuration for a magnesium (Mg) atom. Answer: 1s2 2s2 2p6 3s2 Expla-
nation: Magnesium, atomic number 12, has 12 electrons: 1s2 (2), 2s2 (2), 2p6 (6), and 3s2
(2). The 3s2 electrons are valence electrons, which magnesium loses to form Mg2+ ions, as
seen in ionic compounds like MgO.
2.8 Question 8
How many valence electrons does an oxygen (O) atom have? Answer: 6 Explanation:
Oxygen, atomic number 8, has the configuration 1s2 2s2 2p4 . Valence electrons in the n=2
shell include 2s2 (2) and 2p4 (4), totaling 6. These electrons enable oxygen to form two
covalent bonds, as in H2 O, or gain two electrons to achieve a stable octet.
Prepared for 2025 Exam
, CHEM 103 Module 4 Exam 2025 3
2.9 Question 9
What is the electron configuration for a sodium (Na) atom? Answer: 1s2 2s2 2p6 3s1 Expla-
nation: Sodium, atomic number 11, has 11 electrons: 1s2 (2), 2s2 (2), 2p6 (6), and 3s1 (1).
The single 3s electron is highly reactive, driving sodium to lose it and form Na+ ions in
compounds like NaCl.
2.10 Question 10
Write the electron configuration for an aluminum (Al) atom. Answer: 1s2 2s2 2p6 3s2 3p1
Explanation: Aluminum, atomic number 13, has 13 electrons: 1s2 (2), 2s2 (2), 2p6 (6), 3s2
(2), and 3p1 (1). The 3s2 3p1 electrons are valence electrons, enabling aluminum to form
three bonds or lose three electrons to form Al3+ .
3. Orbital Diagrams
3.1 Question 11
Draw the orbital diagram for a nitrogen (N) atom. Answer: 1s2 ↑↓ 2s2 ↑↓ 2p3 ↑↑↑ Explana-
tion: Nitrogen, atomic number 7, has the configuration 1s2 2s2 2p3 . The 1s and 2s orbitals
are filled with paired electrons (opposite spins). The 2p subshell has three orbitals, each
occupied by one unpaired electron per Hund’s rule, which favors parallel spins to minimize
repulsion, resulting in ↑↑↑.
3.2 Question 12
Provide the orbital diagram for a carbon (C) atom. Answer: 1s2 ↑↓ 2s2 ↑↓ 2p2 ↑↑ Expla-
nation: Carbon, atomic number 6, has the configuration 1s2 2s2 2p2 . The 1s and 2s orbitals
are paired. The 2p subshell has two electrons in separate orbitals with parallel spins (↑↑)
per Hund’s rule, enabling carbon to form four bonds through hybridization.
3.3 Question 13
What is the orbital diagram for a fluorine (F) atom? Answer: 1s2 ↑↓ 2s2 ↑↓ 2p5 ↑↓↑↓↑
Explanation: Fluorine, atomic number 9, has the configuration 1s2 2s2 2p5 . The 1s and 2s
orbitals are paired. The 2p subshell has three orbitals: two with paired electrons (↑↓) and
one with a single electron (↑), reflecting fluorine’s high reactivity as it seeks one electron for
a stable octet.
3.4 Question 14
Draw the orbital diagram for a boron (B) atom. Answer: 1s2 ↑↓ 2s2 ↑↓ 2p1 ↑ Explanation:
Boron, atomic number 5, has the configuration 1s2 2s2 2p1 . The 1s and 2s orbitals are paired,
while the 2p subshell has one electron in a single orbital (↑), enabling boron to form three
bonds, as in BF3 .
Prepared for 2025 Exam
