CHEM 103 | CHEM103 Exam 1: General Chemistry
Updated and Latest Questions and Correct
Answers with Rationale - Portage Learning
1. An atom of Nitrogen-15 has how many neutrons in its nucleus?
A. 7
B. 15
C. 8
D. 14
Correct Answer: C
Expert Explanation: Nitrogen always has an atomic number of 7, which represents the
number of protons. The mass number of 15 is the sum of protons and neutrons. By
subtracting the atomic number from the mass number, we find there are 8 neutrons.
Option A is incorrect because 7 represents only the protons. Option C and D do not
represent the correct subatomic count for this isotope.
2. Which of the following describes two atoms that are isotopes of each other?
A. Same number of protons, different number of electrons
B. Same number of neutrons, different number of protons
C. Same mass number, different atomic number
D. Same number of protons, different number of neutrons
Correct Answer: D
Expert Explanation: Isotopes are atoms of the same element with different masses.
Because they are the same element, they must have the same number of protons. The
difference in mass arises from a different number of neutrons in the nucleus. Option D
describes ions rather than isotopes because it involves electron counts. This concept is vital
for understanding why atomic masses on the periodic table are not whole numbers.
3. Which element has the following ground-state electron configuration: 1s² 2s² 2p⁶ 3s² 3p⁴?
A. Oxygen
B. Chlorine
C. Silicon
D. Sulfur
Correct Answer: D
,Expert Explanation: To identify the element, sum the total number of electrons in the
configuration, which is 16. In a neutral atom, the number of electrons equals the number of
protons or the atomic number. Looking at the periodic table, sulfur is the element with
atomic number 16. Oxygen has only 8 electrons, while silicon has 14 and chlorine has 17.
Therefore, Sulfur is the only correct identification for this specific electron arrangement.
4. What is the correct chemical formula for the ionic compound formed between Calcium and
Nitrogen?
A. CaN
B. Ca2N3
C. Ca3N2
D. CaN2
Correct Answer: C
Expert Explanation: Calcium is in group 2 and consistently forms a +2 cation. Nitrogen is
in group 15 and typically forms a -3 anion. To create a neutral compound, the total positive
and negative charges must balance to zero. Using three calcium ions (+6 total) and two
nitride ions (-6 total) achieves this balance. Thus, the formula must be Ca3N2, making
option C the correct choice.
5. Which of the following elements has the largest atomic radius?
A. Fluorine
B. Lithium
C. Cesium
D. Potassium
Correct Answer: C
Expert Explanation: Atomic radius increases as you move down a group and decreases as
you move across a period. Cesium is located at the bottom of the first group, giving it the
most occupied electron shells. Fluorine is at the top right, making it one of the smallest
atoms. Potassium is also in the first group but sits higher than Cesium. Therefore, Cesium
possesses the largest atomic radius among the options provided.
6. What is the name of the compound with the formula N2O4?
A. Nitrogen oxide
B. Nitrogen(IV) oxide
C. Dinitrogen tetroxide
D. Dinitrogen quadroxide
, Correct Answer: C
Expert Explanation: N2O4 is a molecular compound composed of two nonmetals.
Molecular nomenclature uses Greek prefixes to indicate the number of atoms of each
element. ‘Di-’ signifies two nitrogen atoms, and ‘tetra-’ signifies four oxygen atoms. The
prefix ‘tetra-’ drops the ‘a’ before ‘oxide’ to become ‘tetroxide’. This follows the standard
IUPAC rules for naming binary covalent molecules.
7. How many valence electrons are present in an atom of Phosphorus?
A. 3
B. 5
C. 15
D. 8
Correct Answer: B
Expert Explanation: Phosphorus is located in Group 15 of the periodic table. For main
group elements, the number of valence electrons corresponds to the last digit of the group
number. Phosphorus has an atomic number of 15, meaning its configuration is [Ne] 3s² 3p³.
The outermost shell (n=3) contains a total of five electrons. This count determines how the
atom will bond with other elements.
8. Which trend correctly describes electronegativity across the periodic table?
A. Increases down a group and increases across a period
B. Decreases down a group and decreases across a period
C. Decreases down a group and increases across a period
D. Increases down a group and decreases across a period
Correct Answer: C
Expert Explanation: Electronegativity measures an atom’s ability to attract shared
electrons in a bond. It generally increases as you move from left to right across a period due
to increased nuclear charge. It decreases as you move down a group because the valence
electrons are further from the nucleus. Fluorine is the most electronegative element, sitting
at the top right. Conversely, Francium at the bottom left has the lowest electronegativity.
9. The correct name for the ion SO4²⁻ is:
A. Sulfate
B. Sulfide
C. Sulfite
D. Sulfur tetroxide
Updated and Latest Questions and Correct
Answers with Rationale - Portage Learning
1. An atom of Nitrogen-15 has how many neutrons in its nucleus?
A. 7
B. 15
C. 8
D. 14
Correct Answer: C
Expert Explanation: Nitrogen always has an atomic number of 7, which represents the
number of protons. The mass number of 15 is the sum of protons and neutrons. By
subtracting the atomic number from the mass number, we find there are 8 neutrons.
Option A is incorrect because 7 represents only the protons. Option C and D do not
represent the correct subatomic count for this isotope.
2. Which of the following describes two atoms that are isotopes of each other?
A. Same number of protons, different number of electrons
B. Same number of neutrons, different number of protons
C. Same mass number, different atomic number
D. Same number of protons, different number of neutrons
Correct Answer: D
Expert Explanation: Isotopes are atoms of the same element with different masses.
Because they are the same element, they must have the same number of protons. The
difference in mass arises from a different number of neutrons in the nucleus. Option D
describes ions rather than isotopes because it involves electron counts. This concept is vital
for understanding why atomic masses on the periodic table are not whole numbers.
3. Which element has the following ground-state electron configuration: 1s² 2s² 2p⁶ 3s² 3p⁴?
A. Oxygen
B. Chlorine
C. Silicon
D. Sulfur
Correct Answer: D
,Expert Explanation: To identify the element, sum the total number of electrons in the
configuration, which is 16. In a neutral atom, the number of electrons equals the number of
protons or the atomic number. Looking at the periodic table, sulfur is the element with
atomic number 16. Oxygen has only 8 electrons, while silicon has 14 and chlorine has 17.
Therefore, Sulfur is the only correct identification for this specific electron arrangement.
4. What is the correct chemical formula for the ionic compound formed between Calcium and
Nitrogen?
A. CaN
B. Ca2N3
C. Ca3N2
D. CaN2
Correct Answer: C
Expert Explanation: Calcium is in group 2 and consistently forms a +2 cation. Nitrogen is
in group 15 and typically forms a -3 anion. To create a neutral compound, the total positive
and negative charges must balance to zero. Using three calcium ions (+6 total) and two
nitride ions (-6 total) achieves this balance. Thus, the formula must be Ca3N2, making
option C the correct choice.
5. Which of the following elements has the largest atomic radius?
A. Fluorine
B. Lithium
C. Cesium
D. Potassium
Correct Answer: C
Expert Explanation: Atomic radius increases as you move down a group and decreases as
you move across a period. Cesium is located at the bottom of the first group, giving it the
most occupied electron shells. Fluorine is at the top right, making it one of the smallest
atoms. Potassium is also in the first group but sits higher than Cesium. Therefore, Cesium
possesses the largest atomic radius among the options provided.
6. What is the name of the compound with the formula N2O4?
A. Nitrogen oxide
B. Nitrogen(IV) oxide
C. Dinitrogen tetroxide
D. Dinitrogen quadroxide
, Correct Answer: C
Expert Explanation: N2O4 is a molecular compound composed of two nonmetals.
Molecular nomenclature uses Greek prefixes to indicate the number of atoms of each
element. ‘Di-’ signifies two nitrogen atoms, and ‘tetra-’ signifies four oxygen atoms. The
prefix ‘tetra-’ drops the ‘a’ before ‘oxide’ to become ‘tetroxide’. This follows the standard
IUPAC rules for naming binary covalent molecules.
7. How many valence electrons are present in an atom of Phosphorus?
A. 3
B. 5
C. 15
D. 8
Correct Answer: B
Expert Explanation: Phosphorus is located in Group 15 of the periodic table. For main
group elements, the number of valence electrons corresponds to the last digit of the group
number. Phosphorus has an atomic number of 15, meaning its configuration is [Ne] 3s² 3p³.
The outermost shell (n=3) contains a total of five electrons. This count determines how the
atom will bond with other elements.
8. Which trend correctly describes electronegativity across the periodic table?
A. Increases down a group and increases across a period
B. Decreases down a group and decreases across a period
C. Decreases down a group and increases across a period
D. Increases down a group and decreases across a period
Correct Answer: C
Expert Explanation: Electronegativity measures an atom’s ability to attract shared
electrons in a bond. It generally increases as you move from left to right across a period due
to increased nuclear charge. It decreases as you move down a group because the valence
electrons are further from the nucleus. Fluorine is the most electronegative element, sitting
at the top right. Conversely, Francium at the bottom left has the lowest electronegativity.
9. The correct name for the ion SO4²⁻ is:
A. Sulfate
B. Sulfide
C. Sulfite
D. Sulfur tetroxide
