ATI TEAS Chemistry: Atoms, Reactions, Solutions, and pH

The six Chemistry objectives and what 8 items means

ATI's Version 7 content outline names six Chemistry objectives: recognize basic atomic structure, explain the physical properties and changes of matter, describe chemical reactions, demonstrate how conditions affect reactions, understand properties of solutions, and describe concepts of acids and bases. Together they move from what matter is, to how it changes, to how substances behave in reactions and solutions.

ATI assigns 8 scored items to Chemistry, out of 44 scored Science items. That number covers the whole category. It does not mean every objective gets an item on your form, and it cannot tell you which concepts will appear.

ATI's exam-details page still lists Version 7 as live as of October 2026, with no successor announced, so these six objectives apply to 2027 test dates unless ATI publishes a dated change. The ATI TEAS Science study guide shows how Chemistry fits beside A&P, Biology, and Scientific Reasoning.

Atomic structure explains chemical behavior

Start with the three particles. The number of protons is the atomic number, and it defines the element: every atom with 6 protons is carbon. Neutrons add mass, and the mass number is protons plus neutrons. Atoms of the same element with different numbers of neutrons are isotopes. Electrons carry the negative charge and do the work in bonding.

Keep three ideas connected:

• Atomic number: the number of protons.
• Mass number: protons plus neutrons in a particular atom.
• Charge: the imbalance between protons and electrons. A neutral atom has equal numbers.

An ion forms when an atom gains or loses electrons. Take an original example: a neutral atom has 12 protons and 12 electrons. If it loses two electrons, it still has 12 protons and is still the same element, but now it carries a 2+ charge. The useful question is not only "What is the charge?" but "Which particle count changed?" Changing the proton count would change the element.

Bonding follows the same logic. In an ionic bond, electrons transfer from one atom to another and the resulting oppositely charged ions attract. In a covalent bond, two atoms share electrons. Focus on what happens to the electrons.

Separate properties from changes of matter

A property describes matter. A change describes what happens to it. A physical property, such as color, density, or boiling point, can be measured without changing what the substance is. A chemical property, such as iron's ability to combine with oxygen, describes how a substance can react to form something new.

Physical change versus chemical change

Decide from evidence about composition:

Appearance alone is not decisive. Gas bubbles can signal a chemical change, but only when the substance is not simply boiling, because boiling is a change of state. A color change counts as evidence only when a new colored substance forms, not when two colors just mix.

When you miss a change question, write one sentence naming the evidence. "It looks different" is weak. "A new substance formed with different properties" addresses the real distinction.

Read reactions at particle and equation levels

A chemical reaction rearranges atoms into new combinations. Atoms are conserved, so a balanced equation shows the same number of each element on both sides.

Coefficient versus subscript

This distinction prevents the most common balancing error:

• A subscript is part of a formula and tells how many atoms of an element are in one unit.
• A coefficient goes in front of a formula and tells how many units take part.

In 2H₂O, the subscript 2 belongs to hydrogen inside each water molecule, and the coefficient 2 means two molecules: four hydrogen atoms and two oxygen atoms in total. You balance by changing coefficients only. Changing H₂O to H₂O₂ would not balance water; it would turn it into hydrogen peroxide, a different compound.

For an original balancing example, start with N₂ + H₂ → NH₃. Put 2 in front of NH₃ to balance nitrogen (2 on each side). That makes six hydrogen atoms on the product side, so put 3 in front of H₂: N₂ + 3H₂ → 2NH₃. Recount: 2 N and 6 H on each side.

ATI's public question-types page uses this count, adjust, recount routine as its example of an ordered-response item, so practice saying the steps in order, not just getting the final coefficients. If equations still blur together, practice balancing and reaction questions with explanations in full ATI TEAS prep → and name what each number controls.

Conditions change how fast a reaction runs

ATI lists how conditions affect reactions as its own objective. Collision theory ties the conditions together: particles react only when they collide with enough energy and the right orientation.

• Temperature: higher temperature gives particles more kinetic energy, so collisions are more frequent and more of them have enough energy. Rate usually rises.
• Concentration: more reactant particles in the same space means more collisions.
• Surface area: for a solid, only surface particles can collide with the other reactant, so cutting or crushing it speeds the reaction.
• Catalyst: speeds the reaction by providing a pathway with lower activation energy, without being consumed.

An original comparison makes the logic visible. Two equal solid samples react with the same solution under identical conditions, but one sample is crushed into small pieces. If the crushed sample reacts faster, the evidence supports surface area as the changed condition. It does not show that the crushed sample became a different substance.

Keep rate and amount separate. A catalyst or a crushed solid changes how fast product forms. How much product can form still depends on the amounts of the reactants, and the one that runs out first sets the limit.

Solutions: name the solute, solvent, and evidence

A solution is a homogeneous mixture. The solvent is the major component, and each minor component that dissolves in it is a solute: in salt water, salt is the solute and water is the solvent. Concentration describes how much solute is present in a given amount of solution or solvent.

Use a three-question evidence check:

1. What is the solute?
2. What is the solvent?
3. What observation supports the claim about concentration or solubility?

Suppose Cup A and Cup B each hold 200 mL of water at the same temperature. Four grams of a substance dissolve completely in Cup A, and eight grams dissolve completely in Cup B. Cup B has more dissolved solute in the same volume, so it is more concentrated. The observation does not show the maximum solubility, because both amounts dissolved completely and no limit was reached.

Terms such as dilute, concentrated, saturated, and unsaturated answer different questions. "Concentrated" compares amounts of solute on the same basis. Solubility is the maximum amount of solute that can dissolve in a given amount of solvent at a given temperature, and a saturated solution has reached that maximum. A concentrated solution is not automatically saturated. When those claims keep tripping you up, revisit missed solution and concentration questions with Fix It in full ATI TEAS prep →.

Acids and bases: read pH as a power of ten

The pH scale runs from 0 to 14, with 7 neutral. Below 7 is acidic and above 7 is basic. A lower pH means more free hydrogen ions relative to hydroxide ions.

pH is logarithmic: each whole unit is a factor of ten. A solution at pH 3 is 10 × 10 × 10 = 1,000 times as acidic as one at pH 6, not "3 units" more acidic in a simple sense. A pH value describes the solution; it does not tell you which acid or base produced it.

Decide from the pH or chemical information given, not from a familiar product name.

In a neutralization reaction, an acid and a base react to form water and a salt. The resulting salt solution is not always exactly pH 7, because the ions formed can make it slightly acidic or basic. Keep this at the chemical level. It is not advice about treating exposures or changing body pH.

Diagnose chemistry errors before adding notes

After each missed or guessed problem, classify the error:

This turns "I missed Chemistry" into a cause you can fix. For a quick wider check, use the free ATI TEAS practice questions and classify the reasoning behind each Science answer.

Build a chemistry review cycle

Pick one of the six objectives and run a short cycle:

1. Explain the core distinction without notes.
2. Work one original example in words, symbols, or a diagram.
3. Name the evidence that supports the answer.
4. Record the error type if you missed it or guessed.
5. Come back later with a different representation of the same idea.

Don't replace this with recalled live questions. ATI's outline defines which objectives can be tested; actual forms are not public. When you are ready to mix the six objectives, add Chemistry to mixed Science practice in full ATI TEAS prep → and check the reasoning before the arithmetic.