HESI A2 CHEMISTRY ACTUAL EXAM 2026/2027 | 150
Questions with Correct Detailed Answers & Rationale |
Already A Graded | New & Revised | Elsevier Blueprint
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Part 1: Atomic Structure & Periodic Table
Building the foundation—understanding what matter is made of and how elements
organize themselves.
Q1: A nurse is reviewing a patient's imaging report that mentions "isotopes used in PET
scans." An isotope of an element has which characteristic?
A. A different number of protons than the standard atom
B. A different number of electrons than the standard atom
C. A different number of neutrons than the standard atom [CORRECT]
D. A different chemical reactivity than the standard atom
Correct Answer: C
Rationale: Isotopes are atoms of the same element with the same number of protons
but different numbers of neutrons, resulting in different mass numbers. They have
identical chemical properties (same electron configuration) but different nuclear
stability. PET scans use radioactive isotopes like fluorine-18. Option A describes a
,different element entirely. Option B describes ions, not isotopes. Option D is incorrect
because chemical reactivity depends on electrons, which remain the same in isotopes.
Q2: Which subatomic particle carries a positive charge and contributes to the atomic
mass?
A. Electron, found in orbitals surrounding the nucleus
B. Neutron, with mass but no charge
C. Proton, located in the nucleus with +1 charge [CORRECT]
D. Photon, carrying electromagnetic energy
Correct Answer: C
Rationale: Protons reside in the nucleus, carry a +1 charge, and have a mass of
approximately 1 amu, contributing directly to atomic mass. Electrons (A) are negative
and have negligible mass. Neutrons (B) contribute mass but are neutral. Photons (D) are
energy particles, not subatomic components of atoms. The atomic mass is essentially
the sum of protons plus neutrons, with electrons contributing almost nothing to mass
but determining chemical behavior.
Q3: An element has an atomic number of 17 and a mass number of 37. How many
neutrons does this atom contain?
A. 17 neutrons, equal to the atomic number
B. 20 neutrons, calculated as mass number minus atomic number [CORRECT]
C. 37 neutrons, equal to the mass number
,D. 54 neutrons, the sum of protons and mass number
Correct Answer: B
Rationale: The number of neutrons equals the mass number minus the atomic number
(37 - 17 = 20). The atomic number (17) gives protons (and electrons in a neutral atom).
The mass number is protons plus neutrons. This element is chlorine-37, a naturally
occurring isotope of chlorine. Option A confuses atomic number with neutron count.
Option C mistakes mass number for neutron count. Option D incorrectly adds the
numbers.
Q4: Which element in Period 3 has the electron configuration [Ne] 3s²3p⁴?
A. Silicon (Si), with configuration ending in 3p²
B. Phosphorus (P), with configuration ending in 3p³
C. Sulfur (S), with six valence electrons [CORRECT]
D. Chlorine (Cl), with configuration ending in 3p⁵
Correct Answer: C
Rationale: [Ne] 3s²3p⁴ indicates 2 + 4 = 6 valence electrons, placing this in Group 16.
Counting from neon (atomic number 10): 10 + 2 + 4 = 16, which is sulfur. Silicon (A) has
4 valence electrons (3s²3p²). Phosphorus (B) has 5 valence electrons (3s²3p³). Chlorine
(D) has 7 valence electrons (3s²3p⁵). This configuration shows sulfur's position in
Period 3, Group 16, with its characteristic six valence electrons.
Q5: A nursing student needs to identify which element has the highest electronegativity.
Looking at Period 2, which element attracts electrons most strongly?
, A. Lithium (Li), the leftmost element in Period 2
B. Carbon (C), in the middle of the period
C. Fluorine (F), the rightmost element before neon [CORRECT]
D. Neon (Ne), the noble gas at the end
Correct Answer: C
Rationale: Electronegativity increases across a period (left to right) and decreases down
a group. Fluorine is the most electronegative element (4.0 on the Pauling scale)
because it has high nuclear charge with minimal electron shielding in Period 2. Lithium
(A) has low electronegativity (1.0). Carbon (B) is intermediate (2.5). Neon (D) is a noble
gas with a complete octet and essentially zero electronegativity—it doesn't attract
additional electrons. This trend is crucial for predicting bond polarity.
Q6: Which periodic trend describes the energy required to remove an electron from a
gaseous atom?
A. Electronegativity, the attraction for bonding electrons
B. Ionization energy, the energy to remove an electron [CORRECT]
C. Atomic radius, the size of the atom
D. Electron affinity, the energy change when adding an electron
Correct Answer: B
Rationale: Ionization energy is defined as the minimum energy required to remove the
most loosely bound electron from a neutral gaseous atom. It increases across a period
and decreases down a group. Electronegativity (A) measures attraction in chemical
Questions with Correct Detailed Answers & Rationale |
Already A Graded | New & Revised | Elsevier Blueprint
Aligned | Pass Guaranteed
Part 1: Atomic Structure & Periodic Table
Building the foundation—understanding what matter is made of and how elements
organize themselves.
Q1: A nurse is reviewing a patient's imaging report that mentions "isotopes used in PET
scans." An isotope of an element has which characteristic?
A. A different number of protons than the standard atom
B. A different number of electrons than the standard atom
C. A different number of neutrons than the standard atom [CORRECT]
D. A different chemical reactivity than the standard atom
Correct Answer: C
Rationale: Isotopes are atoms of the same element with the same number of protons
but different numbers of neutrons, resulting in different mass numbers. They have
identical chemical properties (same electron configuration) but different nuclear
stability. PET scans use radioactive isotopes like fluorine-18. Option A describes a
,different element entirely. Option B describes ions, not isotopes. Option D is incorrect
because chemical reactivity depends on electrons, which remain the same in isotopes.
Q2: Which subatomic particle carries a positive charge and contributes to the atomic
mass?
A. Electron, found in orbitals surrounding the nucleus
B. Neutron, with mass but no charge
C. Proton, located in the nucleus with +1 charge [CORRECT]
D. Photon, carrying electromagnetic energy
Correct Answer: C
Rationale: Protons reside in the nucleus, carry a +1 charge, and have a mass of
approximately 1 amu, contributing directly to atomic mass. Electrons (A) are negative
and have negligible mass. Neutrons (B) contribute mass but are neutral. Photons (D) are
energy particles, not subatomic components of atoms. The atomic mass is essentially
the sum of protons plus neutrons, with electrons contributing almost nothing to mass
but determining chemical behavior.
Q3: An element has an atomic number of 17 and a mass number of 37. How many
neutrons does this atom contain?
A. 17 neutrons, equal to the atomic number
B. 20 neutrons, calculated as mass number minus atomic number [CORRECT]
C. 37 neutrons, equal to the mass number
,D. 54 neutrons, the sum of protons and mass number
Correct Answer: B
Rationale: The number of neutrons equals the mass number minus the atomic number
(37 - 17 = 20). The atomic number (17) gives protons (and electrons in a neutral atom).
The mass number is protons plus neutrons. This element is chlorine-37, a naturally
occurring isotope of chlorine. Option A confuses atomic number with neutron count.
Option C mistakes mass number for neutron count. Option D incorrectly adds the
numbers.
Q4: Which element in Period 3 has the electron configuration [Ne] 3s²3p⁴?
A. Silicon (Si), with configuration ending in 3p²
B. Phosphorus (P), with configuration ending in 3p³
C. Sulfur (S), with six valence electrons [CORRECT]
D. Chlorine (Cl), with configuration ending in 3p⁵
Correct Answer: C
Rationale: [Ne] 3s²3p⁴ indicates 2 + 4 = 6 valence electrons, placing this in Group 16.
Counting from neon (atomic number 10): 10 + 2 + 4 = 16, which is sulfur. Silicon (A) has
4 valence electrons (3s²3p²). Phosphorus (B) has 5 valence electrons (3s²3p³). Chlorine
(D) has 7 valence electrons (3s²3p⁵). This configuration shows sulfur's position in
Period 3, Group 16, with its characteristic six valence electrons.
Q5: A nursing student needs to identify which element has the highest electronegativity.
Looking at Period 2, which element attracts electrons most strongly?
, A. Lithium (Li), the leftmost element in Period 2
B. Carbon (C), in the middle of the period
C. Fluorine (F), the rightmost element before neon [CORRECT]
D. Neon (Ne), the noble gas at the end
Correct Answer: C
Rationale: Electronegativity increases across a period (left to right) and decreases down
a group. Fluorine is the most electronegative element (4.0 on the Pauling scale)
because it has high nuclear charge with minimal electron shielding in Period 2. Lithium
(A) has low electronegativity (1.0). Carbon (B) is intermediate (2.5). Neon (D) is a noble
gas with a complete octet and essentially zero electronegativity—it doesn't attract
additional electrons. This trend is crucial for predicting bond polarity.
Q6: Which periodic trend describes the energy required to remove an electron from a
gaseous atom?
A. Electronegativity, the attraction for bonding electrons
B. Ionization energy, the energy to remove an electron [CORRECT]
C. Atomic radius, the size of the atom
D. Electron affinity, the energy change when adding an electron
Correct Answer: B
Rationale: Ionization energy is defined as the minimum energy required to remove the
most loosely bound electron from a neutral gaseous atom. It increases across a period
and decreases down a group. Electronegativity (A) measures attraction in chemical
