HESI Chemistry Test Overview

The Chemistry section of the HESI A2 exam evaluates a student’s understanding of fundamental chemistry concepts. Importantly, this is one of the sections that many nursing and allied health programs do not require — unlike the core sections of Math, Reading Comprehension, Vocabulary, and Grammar, which are nearly universal. Before investing significant preparation time, confirm with your specific programs whether Chemistry is actually on your required list. That said, for programs that do require it, a working knowledge of chemical principles is essential for understanding pharmacology, metabolism, fluid and electrolyte balance, and many other core healthcare topics.

Purpose and Context

Chemistry forms the molecular foundation of biology and medicine. Understanding how atoms bond, how solutions behave, and how chemical reactions proceed helps students make sense of processes like drug interactions, acid-base balance in the blood, and cellular energy production. The HESI Chemistry section confirms that applicants have enough scientific grounding to engage meaningfully with these concepts in their coursework.

Test Format

Like the Biology section, Chemistry typically consists of 25 questions allotted in approximately 25 minutes. It is computer-based and entirely multiple choice. The short question count means each item carries significant weight, making broad preparation across all topic areas important.

Topics and Skills Assessed

Atomic Structure Questions in this area cover the basic structure of the atom — protons, neutrons, and electrons, their charges, and where they are located. You should understand atomic number, mass number, and how to determine the number of each subatomic particle from an element’s notation. Isotopes — atoms of the same element with different numbers of neutrons — are also tested.

The Periodic Table You should be familiar with how the periodic table is organized and what information it conveys. This includes understanding periods and groups, and the general trends associated with them — such as electronegativity, atomic radius, and ionization energy. Knowing the properties of major element families, including alkali metals, halogens, and noble gases, is helpful.

Chemical Bonding This topic covers how and why atoms bond with one another. Ionic bonds form between metals and nonmetals through the transfer of electrons, while covalent bonds form through electron sharing between nonmetals. You should understand the differences between these bond types and be able to identify which type a given compound is likely to have. Polar and nonpolar covalent bonds, and how electronegativity differences determine polarity, may also appear.

Chemical Reactions and Equations Questions here assess your ability to recognize and balance basic chemical equations, understand the law of conservation of mass, and identify different reaction types — including synthesis, decomposition, single replacement, and double replacement reactions. Knowing what reactants and products are, and how coefficients and subscripts function in a chemical formula, is essential.

Stoichiometry Stoichiometry involves using the relationships in a balanced chemical equation to calculate quantities of reactants or products. Questions are generally introductory in nature — you may be asked to use molar ratios or interpret what a balanced equation tells you about the proportions of substances involved. A basic understanding of the mole concept and molar mass is helpful here.

States of Matter and Gas Laws You should understand the three states of matter — solid, liquid, and gas — and the transitions between them. Basic gas laws, including Boyle’s Law (pressure and volume) and Charles’s Law (temperature and volume), may appear. Understanding how temperature and pressure affect the behavior of gases is the core skill being assessed.

Solutions and Concentration This area covers how solutes dissolve in solvents to form solutions, the factors that affect solubility, and basic concepts of concentration. Understanding molarity — the number of moles of solute per liter of solution — is important. The concepts of dilution and saturation may also appear.

Acids, Bases, and pH Acid-base chemistry is one of the most clinically relevant topics on the Chemistry section. You should understand the definitions of acids and bases, the pH scale, and what it means for a solution to be acidic, basic, or neutral. The concept of neutralization reactions — an acid and base combining to form water and a salt — is also tested. This topic connects directly to important clinical concepts like blood pH and acid-base disorders.

Nuclear Chemistry Basic concepts of radioactivity appear on some versions of the exam. This includes understanding alpha, beta, and gamma radiation, what radioactive decay means, and the concept of half-life. Questions are generally conceptual rather than computational.

Scoring

Chemistry is scored on the same 0–100% scale as all HESI A2 sections. Most programs require a minimum of 75%, though more selective programs may set the bar higher. As with Biology, the 25-question format means each correct answer is particularly valuable.

How It Compares to Other Sections

Chemistry is widely considered one of the more challenging sections of the HESI A2, particularly for students who have been away from science coursework for several years or who never took a dedicated chemistry course. The concepts are abstract by nature and require genuine understanding rather than memorization alone. That said, the HESI Chemistry section is introductory in scope — it does not venture into advanced organic chemistry or complex calculations — and focused preparation can make a significant difference.

Preparation Tips

Start with atomic structure and the periodic table. These are the building blocks for nearly every other topic on the test. Getting comfortable with them first makes subsequent topics easier to absorb.

Focus on conceptual understanding. Most Chemistry questions test whether you understand how and why things work, not whether you can perform complex calculations. Prioritize comprehension over formula memorization.

Pay special attention to acids, bases, and pH. This topic is both heavily tested and directly relevant to clinical practice, making it one of the highest-yield areas to study.

Use the official Elsevier HESI Admission Assessment Exam Review. This guide provides the most exam-accurate practice questions available and is the single best preparation resource for this section.

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Overall, the HESI Chemistry section is conquerable with focused preparation, even for students without a strong science background. Prioritizing the highest-yield topics — atomic structure, bonding, acids and bases, and solutions — and building genuine conceptual understanding will position you well for a strong score.