CHEMISTRY STARTS HERE
GRADE 9 • UNIT 1: MATTER & MEASUREMENT
Big Idea
Chemistry is the study of matter, its properties, how it changes, and the energy involved in those changes. In
this unit, you learn the language chemists use to describe matter precisely.
UNIT ROADMAP
Matter & classification → properties & changes → measurements → SI units → density → scientific
notation → significant figures → dimensional analysis → data quality → application.
What you should be able to do
• Classify samples as elements, compounds, homogeneous mixtures, or heterogeneous mixtures.
• Distinguish physical properties/changes from chemical properties/changes.
• Choose appropriate SI units and convert between units using factor-label reasoning.
• Calculate density and rearrange the density equation to solve for mass or volume.
• Use scientific notation and significant figures correctly.
• Set up dimensional-analysis conversions so units cancel logically.
• Evaluate measurements using accuracy, precision, and percent error.
Why this matters
Every later chemistry topic depends on measurement. A balanced equation, a concentration, a reaction rate, or
a lab result is only as good as the measurements and units behind it.
U.S.-STYLE SCIENCE HABIT
Do not only state an answer. Show the measurement + unit + reasoning. A strong scientific explanation
connects observations to a model or calculation.
U.S. HIGH SCHOOL CHEMISTRY | GRADE 9 | UNIT 1 Page 1
, 1. Matter: What Is It?
Matter is anything that has mass and occupies space. Chemists describe matter at three connected levels: what
we observe, what particles are doing, and the symbols/equations we use.
Level Question Example
Macroscopic What do I observe? A clear liquid has a measured volume.
Particle What are the particles doing? Particles are moving and interacting.
Symbolic How do I represent it? H₂O, NaCl, or a chemical equation.
States of matter
State Particle picture Shape / volume Compressibility
Solid Particles close together; vibrate in place Fixed / fixed Very low
Liquid Particles close; slide past one another Variable / fixed Low
Gas Particles far apart; move freely Variable / variable High
KEY IDEA
A change of state changes particle motion/spacing, not the identity of the substance. Ice, liquid water,
and water vapor are all H₂O.
Quick check
A sealed sample of water is heated until it becomes vapor. Has the substance changed identity? Explain using
particles.
Answer: No. The substance remains H₂O; particles have more kinetic energy and are farther apart.
U.S. HIGH SCHOOL CHEMISTRY | GRADE 9 | UNIT 1 Page 2
, 2. Classifying Matter
Start with one question: Can the composition vary from sample to sample?
Category Composition Can it be separated Example
physically?
Element One type of atom No Cu, O₂
Compound Two or more elements chemically No H₂O, CO₂
bonded in fixed ratios
Homogeneous Uniform throughout; variable Yes Salt water
mixture composition
Heterogeneous Non-uniform; different regions Yes Granite, oil + water
mixture may differ
Element vs compound
An element cannot be broken into simpler substances by ordinary chemical means. A compound contains
different elements chemically bonded in a definite ratio; its properties differ from those of the elements that
form it.
Mixtures: physical combination
• Components keep their own identities.
• Composition can vary.
• Components can be separated by physical methods such as filtration, distillation, evaporation, or
chromatography.
CLASSIFICATION FLOW
1) Is it one pure substance or a mixture? → 2) If pure, element or compound? → 3) If mixture, uniform
(homogeneous) or non-uniform (heterogeneous)?
Practice
Sample Classification Why?
Pure gold, Au Element Only one type of atom.
Carbon dioxide, CO₂ Compound C and O are chemically bonded in a fixed ratio.
Air Homogeneous mixture Different gases are mixed uniformly.
Sand + water Heterogeneous mixture Different parts can be distinguished.
U.S. HIGH SCHOOL CHEMISTRY | GRADE 9 | UNIT 1 Page 3
, 3. Properties & Changes
PHYSICAL PROPERTY
A characteristic that can be observed or measured without changing the substance into a new
substance. Examples: density, melting point, boiling point, color, conductivity, solubility.
CHEMICAL PROPERTY
A characteristic describing how a substance can form new substances. Examples: flammability, ability to
react with oxygen, tendency to corrode or react with acids.
Physical vs chemical change
Type What changes? Examples
Physical change Form, state, size, or arrangement; identity Melting, freezing, cutting, crushing
stays the same
Chemical change Atoms are rearranged into new substance(s) Rusting, burning, decomposing, many
reactions
Evidence of a chemical change
• Formation of a new gas (not simply boiling).
• Formation of a precipitate from solutions.
• Unexpected color change associated with new substances.
• Energy change such as heat or light produced/absorbed during reaction.
• A new odor can be a clue, but should not be used as the only evidence.
DO NOT OVERCLAIM
A temperature change, color change, or bubbles can be evidence, but no single clue automatically
proves a chemical reaction. Ask whether the evidence supports formation of a new substance.
Think like a scientist
Sugar dissolves in water. Is that automatically a chemical change? No. The sugar particles remain sugar
particles; they become dispersed in water. Separation by evaporation can recover sugar.
U.S. HIGH SCHOOL CHEMISTRY | GRADE 9 | UNIT 1 Page 4
GRADE 9 • UNIT 1: MATTER & MEASUREMENT
Big Idea
Chemistry is the study of matter, its properties, how it changes, and the energy involved in those changes. In
this unit, you learn the language chemists use to describe matter precisely.
UNIT ROADMAP
Matter & classification → properties & changes → measurements → SI units → density → scientific
notation → significant figures → dimensional analysis → data quality → application.
What you should be able to do
• Classify samples as elements, compounds, homogeneous mixtures, or heterogeneous mixtures.
• Distinguish physical properties/changes from chemical properties/changes.
• Choose appropriate SI units and convert between units using factor-label reasoning.
• Calculate density and rearrange the density equation to solve for mass or volume.
• Use scientific notation and significant figures correctly.
• Set up dimensional-analysis conversions so units cancel logically.
• Evaluate measurements using accuracy, precision, and percent error.
Why this matters
Every later chemistry topic depends on measurement. A balanced equation, a concentration, a reaction rate, or
a lab result is only as good as the measurements and units behind it.
U.S.-STYLE SCIENCE HABIT
Do not only state an answer. Show the measurement + unit + reasoning. A strong scientific explanation
connects observations to a model or calculation.
U.S. HIGH SCHOOL CHEMISTRY | GRADE 9 | UNIT 1 Page 1
, 1. Matter: What Is It?
Matter is anything that has mass and occupies space. Chemists describe matter at three connected levels: what
we observe, what particles are doing, and the symbols/equations we use.
Level Question Example
Macroscopic What do I observe? A clear liquid has a measured volume.
Particle What are the particles doing? Particles are moving and interacting.
Symbolic How do I represent it? H₂O, NaCl, or a chemical equation.
States of matter
State Particle picture Shape / volume Compressibility
Solid Particles close together; vibrate in place Fixed / fixed Very low
Liquid Particles close; slide past one another Variable / fixed Low
Gas Particles far apart; move freely Variable / variable High
KEY IDEA
A change of state changes particle motion/spacing, not the identity of the substance. Ice, liquid water,
and water vapor are all H₂O.
Quick check
A sealed sample of water is heated until it becomes vapor. Has the substance changed identity? Explain using
particles.
Answer: No. The substance remains H₂O; particles have more kinetic energy and are farther apart.
U.S. HIGH SCHOOL CHEMISTRY | GRADE 9 | UNIT 1 Page 2
, 2. Classifying Matter
Start with one question: Can the composition vary from sample to sample?
Category Composition Can it be separated Example
physically?
Element One type of atom No Cu, O₂
Compound Two or more elements chemically No H₂O, CO₂
bonded in fixed ratios
Homogeneous Uniform throughout; variable Yes Salt water
mixture composition
Heterogeneous Non-uniform; different regions Yes Granite, oil + water
mixture may differ
Element vs compound
An element cannot be broken into simpler substances by ordinary chemical means. A compound contains
different elements chemically bonded in a definite ratio; its properties differ from those of the elements that
form it.
Mixtures: physical combination
• Components keep their own identities.
• Composition can vary.
• Components can be separated by physical methods such as filtration, distillation, evaporation, or
chromatography.
CLASSIFICATION FLOW
1) Is it one pure substance or a mixture? → 2) If pure, element or compound? → 3) If mixture, uniform
(homogeneous) or non-uniform (heterogeneous)?
Practice
Sample Classification Why?
Pure gold, Au Element Only one type of atom.
Carbon dioxide, CO₂ Compound C and O are chemically bonded in a fixed ratio.
Air Homogeneous mixture Different gases are mixed uniformly.
Sand + water Heterogeneous mixture Different parts can be distinguished.
U.S. HIGH SCHOOL CHEMISTRY | GRADE 9 | UNIT 1 Page 3
, 3. Properties & Changes
PHYSICAL PROPERTY
A characteristic that can be observed or measured without changing the substance into a new
substance. Examples: density, melting point, boiling point, color, conductivity, solubility.
CHEMICAL PROPERTY
A characteristic describing how a substance can form new substances. Examples: flammability, ability to
react with oxygen, tendency to corrode or react with acids.
Physical vs chemical change
Type What changes? Examples
Physical change Form, state, size, or arrangement; identity Melting, freezing, cutting, crushing
stays the same
Chemical change Atoms are rearranged into new substance(s) Rusting, burning, decomposing, many
reactions
Evidence of a chemical change
• Formation of a new gas (not simply boiling).
• Formation of a precipitate from solutions.
• Unexpected color change associated with new substances.
• Energy change such as heat or light produced/absorbed during reaction.
• A new odor can be a clue, but should not be used as the only evidence.
DO NOT OVERCLAIM
A temperature change, color change, or bubbles can be evidence, but no single clue automatically
proves a chemical reaction. Ask whether the evidence supports formation of a new substance.
Think like a scientist
Sugar dissolves in water. Is that automatically a chemical change? No. The sugar particles remain sugar
particles; they become dispersed in water. Separation by evaporation can recover sugar.
U.S. HIGH SCHOOL CHEMISTRY | GRADE 9 | UNIT 1 Page 4
