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HESI A2 Chemistry: atomic structure practice questions

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These are original practice items written to the HESI A2 blueprint (4 options, no penalty for wrong answers), not actual exam questions. Try each one before you open the answer.

What this topic covers

Chemistry: atomic structure sits inside the Chemistry section of the HESI A2. Our bank holds 44 verified items tagged to it, and the 4 below are a fixed sample so the page stays the same every time you open it. Each one shows the reasoning, not just the letter.

The topic tag comes from our own items rather than from a published syllabus, so treat it as a map of what we cover. For the official section breakdown see the HESI A2 page.

Chemistry: atomic structure sample questions

Question 1

An atom of the isotope carbon-14 contains 6 protons. How many neutrons are in this isotope?

  1. A 20
  2. B 6
  3. C 14
  4. D 8
Show the answer and explanation

Correct answer: D

The mass number (14) is the sum of protons and neutrons. With 6 protons, neutrons = 14 - 6 = 8.

Why the other options are wrong:
A: This would be the sum of protons and neutrons if there were 14 neutrons, but the mass number is 14, so neutrons cannot be 20.
B: This is the number of protons, not neutrons.
C: This is the mass number (protons + neutrons), not the neutron count alone.

Question 2

A nursing student is studying the composition of an atom. Which subatomic particle has a negative charge and is found in orbitals around the nucleus?

  1. A positron
  2. B neutron
  3. C electron
  4. D proton
Show the answer and explanation

Correct answer: C

Electrons are negatively charged and occupy orbitals around the nucleus.

Why the other options are wrong:
A: Positrons are antimatter particles, not typically found in ordinary atoms.
B: Neutrons have no charge.
D: Protons have a positive charge.

Question 3

An atom of carbon has 6 protons, 6 neutrons, and 6 electrons. What is its atomic number?

  1. A 0
  2. B 12
  3. C 18
  4. D 6
Show the answer and explanation

Correct answer: D

The atomic number is defined as the number of protons in an atom's nucleus. For carbon, this is 6.

Why the other options are wrong:
A: 0 is incorrect; an atom must have at least one proton to be an element.
B: 12 is the mass number (protons + neutrons), not the atomic number.
C: 18 is the sum of all subatomic particles (protons + neutrons + electrons), which is not the atomic number.

Question 4

An atom of an element has an atomic number of 17 and a mass number of 35. How many protons, neutrons, and electrons does a neutral atom of this element have?

  1. A 17 protons, 18 neutrons, 17 electrons
  2. B 17 protons, 35 neutrons, 17 electrons
  3. C 35 protons, 17 neutrons, 35 electrons
  4. D 18 protons, 17 neutrons, 18 electrons
Show the answer and explanation

Correct answer: A

Atomic number = number of protons = 17. Mass number = protons + neutrons, so neutrons = 35 - 17 = 18. In a neutral atom, electrons = protons = 17.

Why the other options are wrong:
B: Neutrons are not equal to the mass number; that would be 35 neutrons, but mass number is sum of protons and neutrons.
C: Protons cannot equal mass number; that would imply zero neutrons, which is incorrect for this isotope.
D: Atomic number defines the element; it cannot be 18 if the atomic number is 17.

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