Chemistry is often the section nursing students dread most on the HESI A2. But here's the good news: the exam tests foundational chemistry concepts, not advanced organic chemistry. With the right study strategy, you can turn this section into a major score booster. This guide covers every topic you'll encounter on exam day.
What the HESI A2 Chemistry Section Covers
The Chemistry section typically includes 30 questions on these core topics:
- Atomic structure and the periodic table
- Chemical bonding (ionic, covalent, hydrogen)
- Chemical reactions and equations
- Solutions, concentrations, and dilutions
- Acids, bases, and pH
- States of matter and phase changes
- Oxidation-reduction reactions
- Nuclear chemistry basics
Atomic Structure: The Building Blocks
Every chemistry question builds on your understanding of atomic structure. Here's what you need to know:
- Protons — positive charge, found in the nucleus, determine the element (atomic number)
- Neutrons — no charge, found in the nucleus, contribute to atomic mass
- Electrons — negative charge, orbit the nucleus in electron shells
Key formulas:
- Atomic number = number of protons
- Mass number = protons + neutrons
- Isotopes = same element, different number of neutrons
- Ions = atoms that gain or lose electrons (cation = positive, anion = negative)
Reading the Periodic Table Like a Pro
The periodic table is your best friend on the HESI A2. Here's how to extract maximum information:
- Groups (columns) — elements share similar chemical properties and valence electrons
- Periods (rows) — elements have the same number of electron shells
- Metals — left side, tend to lose electrons, good conductors
- Nonmetals — right side, tend to gain electrons, poor conductors
- Metalloids — along the staircase line, properties of both
Must-Know Groups
| Group | Name | Key Property |
|---|---|---|
| Group 1 | Alkali Metals | Highly reactive, 1 valence electron |
| Group 2 | Alkaline Earth Metals | Reactive, 2 valence electrons |
| Group 17 | Halogens | Very reactive nonmetals, 7 valence electrons |
| Group 18 | Noble Gases | Stable, full outer shell, unreactive |
Periodic Trends to Memorize
- Electronegativity — increases left → right, decreases top → bottom
- Atomic radius — decreases left → right, increases top → bottom
- Ionization energy — increases left → right, decreases top → bottom
Chemical Bonding
Understanding bond types is essential for the HESI A2:
Ionic Bonds
Formed when one atom transfers electrons to another (metal + nonmetal). Example: NaCl — sodium donates one electron to chlorine. Ionic compounds have high melting points and conduct electricity when dissolved.
Covalent Bonds
Formed when atoms share electrons (nonmetal + nonmetal). Example: H₂O — oxygen shares electrons with two hydrogen atoms. Covalent compounds have lower melting points.
Hydrogen Bonds
Weak bonds between a hydrogen atom bonded to an electronegative atom (O, N, F) and another electronegative atom. Critical in biology — they hold DNA strands together and give water its unique properties.
Chemical Reactions & Balancing Equations
You must be able to identify reaction types and balance simple equations:
Five Reaction Types
- Synthesis: A + B → AB
- Decomposition: AB → A + B
- Single replacement: A + BC → AC + B
- Double replacement: AB + CD → AD + CB
- Combustion: Hydrocarbon + O₂ → CO₂ + H₂O
Balancing Tips
- Balance metals first, then nonmetals, then hydrogen, and oxygen last
- Never change subscripts — only adjust coefficients
- Check your work by counting atoms on both sides
Acids, Bases & pH
This is one of the most heavily tested chemistry topics on the HESI A2:
| Property | Acids | Bases |
|---|---|---|
| pH range | 0–6.9 | 7.1–14 |
| Taste | Sour | Bitter |
| Feel | Sting | Slippery |
| Litmus test | Turns blue → red | Turns red → blue |
| Ions produced | H⁺ (hydrogen) | OH⁻ (hydroxide) |
Key concept: pH 7 is neutral. Each pH unit represents a 10x change in concentration. A pH of 3 is 10 times more acidic than pH 4.
Buffer systems resist changes in pH and are critical in the human body (e.g., bicarbonate buffer in blood maintains pH 7.35–7.45).
Solutions & Concentrations
- Solute — the substance being dissolved
- Solvent — the substance doing the dissolving (usually water)
- Molarity (M) = moles of solute ÷ liters of solution
- Dilution formula: M₁V₁ = M₂V₂
Factors affecting solubility: Temperature (most solids dissolve better in warmer solvents), pressure (affects gas solubility), and polarity ("like dissolves like").
States of Matter & Phase Changes
- Solid → Liquid: Melting (endothermic)
- Liquid → Gas: Evaporation/Boiling (endothermic)
- Gas → Liquid: Condensation (exothermic)
- Liquid → Solid: Freezing (exothermic)
- Solid → Gas: Sublimation (endothermic)
Endothermic = absorbs energy. Exothermic = releases energy.
Oxidation-Reduction (Redox) Reactions
Remember: OIL RIG — Oxidation Is Loss (of electrons), Reduction Is Gain (of electrons).
- The substance that is oxidized is the reducing agent
- The substance that is reduced is the oxidizing agent
Practice Problems
1. An atom has 11 protons, 12 neutrons, and 11 electrons. What is its mass number?
Answer: 23 (protons + neutrons = 11 + 12)
2. What type of bond forms between Na and Cl?
Answer: Ionic bond (metal + nonmetal, electron transfer)
3. A solution has a pH of 2. Is it an acid or base? How does its H⁺ concentration compare to a solution with pH 4?
Answer: Acid. It has 100x more H⁺ ions (10² = 100).
4. Balance: __Fe + __O₂ → __Fe₂O₃
Answer: 4Fe + 3O₂ → 2Fe₂O₃
Your Chemistry Study Plan
- Days 1–3: Atomic structure and periodic table trends
- Days 4–6: Chemical bonding and reaction types
- Days 7–9: Acids, bases, pH, and solutions
- Days 10–12: Practice problems and full chemistry sections
Use our Chemistry flashcards for quick review of elements, formulas, and reaction types. Then test your knowledge with our timed practice tests that simulate real exam conditions.