The Nature of Chemistry

The Ultimate Chemistry Starter Guide: Understanding Matter and How It Changes

Billions of years ago, stars fused hydrogen into heavier elements. When they exploded, those elements scattered through the universe. Some ended up on Earth. Some ended up… in you.
You are made of stardust. So is the soap bubble you blew as a kid. So is the water you drink.
Chemistry is the science that connects it all.
It explores matter in every form—solid, liquid, or gas (and more that have been discovered). It explains how atoms bond, how substances combine, and how even simple changes can create new materials with new properties.
But before you understand any of that, you need to understand what you’re working with first: matter itself—what it’s made of, how it’s classified, how it behaves, and how it changes with energy.

What You’ll Learn:

• Why chemistry is called “the central science”
• What matter is and how to describe it
• How to classify matter by state and composition
• How states of matter behave and why they change
• What signals a true chemical transformation

Key Takeaways

• Chemistry is the science of matter—its composition, properties, changes, and the energy involved in those changes.
• Matter is anything that has mass and takes up space. It is made of tiny particles (atoms, molecules, or ions) that are in constant motion.
• Matter can be classified by its state and composition (pure substances or mixtures).
• States of matter include solids, liquids, and gases.
  • Solids have definite shape and volume; particles vibrate in place.
  • Liquids have definite volume but take the shape of their container; particles move more freely.
  • Gases take both the shape and volume of their container; particles move rapidly and are far apart.
• Pure substances are made of just one type of particle—either elements (like iron) or compounds (like water).
• Mixtures contain two or more substances. They are either homogeneous or heterogeneous.
  • Homogeneous mixtures are uniform throughout (e.g., saltwater, air).
  • Heterogeneous mixtures (e.g., sand in water, granite) have visibly different components.
• Physical properties can be observed without changing the substance’s identity (e.g., color, boiling point, density).
• Physical changes don’t change what the substance is and are often reversible.
• Phase changes are physical changes driven by energy transfer—particles move more or less but don’t change identity.
• Chemical properties describe how substances interact and transform into new materials (e.g., rusting, burning).
• Chemical changes produce new substances with different properties.
• All physical and chemical changes involve energy, either being absorbed or released during the process.
• Energy exists in two main forms: kinetic energy (energy of motion) and potential energy (stored energy)

What is Chemistry?

Chemistry is the science that studies matter—its composition, structure, properties, how it changes, and the energy involved in those changes. Matter is all around you: the air you breathe, the glass in a window, a slice of pizza, and even you. If it has mass and takes up space, it’s matter—and chemistry is all about understanding it.

At its heart, chemistry asks simple but powerful questions: What is this stuff made of? How do different substances interact? How do things change from one form to another, and why? For example, what really happens when metal rusts, when bread bakes, or when fuel burns? Behind all of these everyday things are chemical changes—matter being rearranged with energy involved.

Many students study chemistry because it’s essential for science-related careers. Doctors, engineers, pharmacists, and environmental scientists all rely on chemistry in their work. That’s why chemistry is often called the central science. It connects fields like biology, physics, nuclear science, geology, environmental science, and astronomy among others.

Chemistry is the central science. Chemistry connects and overlaps with many other scientific fields.

But chemistry isn’t just for scientists. It’s part of everyday life and shows up in creative careers too. In the culinary arts, chefs rely on chemistry to transform ingredients — baking bread, tempering chocolate, or creating new flavors all involve chemical reactions. In fashion and beauty, chemistry is behind colors, fabrics, and skincare products. Art conservation depends on chemistry to preserve paintings and sculptures. All these and more back to chemistry.

Even if science isn’t your main interest, learning chemistry helps you make sense of the world around you. It helps you think more logically, solve problems more effectively, and become a more informed part of a world shaped by science and technology.

Everyone learning chemistry begins with the same first step: understanding matter—the “stuff” of the universe. Before exploring how matter changes, chemists first focus on sorting out what kinds of matter exist and how to describe them clearly. To do this, scientists classify matter in two main ways: by state and by composition.

Classification of Matter

To classify matter, it is first important to know what it is made of. This is explained in the kinetic-molecular theory of matter. According to this theory, all matter is made up of tiny particles—atoms, molecules, and ions—that are constantly moving. These particles are so small that we can’t see them with the naked eye, but they form the basic building blocks of everything around us.

Even though we can’t directly see individual particles, we observe the effects of their behavior all the time. When water boils, when metal rusts, when sugar dissolves in tea—these are all things we notice at the macroscopic level, meaning the large-scale world that we can observe with our senses.

But behind the scenes, all of this is happening because of changes at the submicroscopic (or particulate) level—the world of atoms, molecules, and ions. This is where chemistry really happens: particles moving, bonding, separating, and reacting. Understanding this hidden level helps us explain and predict what we see in everyday life.

So when chemists study matter, they’re always thinking of the macroscopic and submicroscopic levels. This allows chemists to classify matter based on its physical state and composition; helping us describe matter clearly, understand how it behaves, and predict how it might change.

The states and compositions of matter. Matter can be classified based on state (solid, liquid, or gas) and composition (pure substances or mixtures)

States of Matter

Matter commonly appears in three physical forms or states: solid, liquid, and gas. Each state behaves differently, both in how it looks and feels on a large (macroscopic) scale and in how its particles act on a smaller (submicroscopic or particulate) scale.

Macroscopic View: How Matter Fills Space

Let’s start with what we can observe with our senses. If you pour water into a glass or open a bottle of perfume, you’re seeing matter behave differently based on its state:

• A solid has a fixed shape and volume, and does not change to match its container. Think of an ice cube in a bowl—it keeps its shape even if the bowl is round. But not all solids are hard or rigid! Solid wax is soft, and solid lead is flexible—so shape is key, not hardness.

• A liquid doesn’t have a fixed shape, but they do have a fixed volume. They flow to take the shape of their container, but only to the extent of their volume. So a glass of water has a flat upper surface—it doesn’t rise up to fill the whole glass unless there’s enough liquid.

• A gas also takes the shape of its container, but unlike a liquid, it fills the entire space available; thus, also taking the volume of the container. That’s why the smell of perfume spreads through a whole room—gas particles move freely and fill all available space. Gases have no surface like liquids do.

Particulate View: How Particles Behave

On the submicroscopic level, the behaviour of matter depends on how close the particles are to one another and how freely they move:

• In a solid, particles are tightly packed in a neat, repeating pattern. They don’t roam freely but vibrate around fixed positions, like people tightly packed in a crowd who can only wiggle in place. This is why solids are able to keep their shape.

• In a liquid, the particles are still close together, but they’re not locked in place nor do they have a regular arrangement. They move around and slide past one another, which allows liquids to flow and take the shape of their container. Unlike solids, the structure is random and constantly shifting.

• In a gas, the particles are far apart and move around very quickly and randomly. They bump into each other and the walls of their container, but they aren’t really “held” by other particles. This freedom of motion lets gases expand and fill any space. Gas particles also have so much space between them, making gases easily compressible.

Comparing the Three States

The three common states of matter. At the macroscopic level, each state of matter has observable differences in shape and volume. At the particulate level, these states differ in how their particles are arranged and how they move.

To help keep things straight, here’s a quick comparison of the key features of each state from the macroscopic view and particulate view:

Property	Solid	Liquid	Gas
Shape	Definite	Indefinite (takes container shape)	Indefinite (fills container)
Volume	Definite	Definite	Indefinite (fills all available space)
Particle arrangement	Tightly packed, in contact, fixed positions, regular pattern	Close together, in contact, not fixed, random pattern	Far apart, random positions
Particle movement	Vibrate in place	Move freely past one another	Move rapidly in random directions
Compressibility	Low	Low	High
Attractive forces between particles	Strong	Moderate	Weak

Phase Changes

Matter can change from one form to another through what we call phase changes or phase transitions. As we mentioned earlier, the kinetic-molecular theory tells us that all matter is made of tiny particles that are always moving.

The more energy these particles have, the faster they move. That’s why solids have particles that move the least, liquids move a bit more, and gases move the most. When a substance gains or loses enough energy—usually in the form of heat—it can switch from one state to another.

Typically, solids melt into liquids, and liquids evaporate into gases when they heat up. The reverse happens when they cool down. But in some cases, solids can turn straight into gases, and gases can turn directly into solids without going through the liquid phase.

Phase changes among solids, liquids, and gases. Melting, vaporization, and sublimation happen when particles gain energy; while freezing, condensation, and deposition occur as particles lose energy.

Here are six common types of phase changes you’ll come across:

Process	Phase Change	Explanation	Example
Melting	Solid → Liquid	Solid absorbs heat; particles move more freely and lose structure	Ice melting into water
Vaporization	Liquid → Gas	Liquid absorbs heat; particles escape into gas phase	Water boiling into steam
Freezing	Liquid → Solid	Liquid loses heat; particles slow and lock into position	Water freezing into ice
Condensation	Gas → Liquid	Gas loses energy; particles clump into liquid	Dew forming on grass
Sublimation	Solid → Gas	Particles gain so much energy they skip the liquid stage	Dry ice (solid carbon dioxide) turning to gas
Deposition	Gas → Solid	Particles lose energy quickly and jump straight to the solid phase	Frost forming from water vapor

Knowing how and why these changes happen helps chemists—and anyone working with materials—understand and control how substances behave. Whether it’s making better packaging, keeping food fresh, or designing spacecraft, it all starts with how matter moves and changes.

Beyond the Basics: More States of Matter

While solids, liquids, and gases are the most familiar states of matter we experience every day, there are other fascinating forms of matter that behave in surprising ways. These states usually appear only under extreme conditions, but they help us better understand how matter works in the universe—and even in technology we use here on Earth.

Plasma: The Electrified State

Plasma is like a gas but made of charged particles—ions and free electrons. It forms when a gas is heated or energized enough to strip electrons from atoms, a phase change known as ionization. The reverse—turning plasma into gas—is also possible through recombination. Plasma conducts electricity, responds to magnetic fields, and often glows.

Plasma. Also known as the fourth state of matter, plasma forms when gas is heated to very high temperatures, causing atoms to lose electrons in a process called ionization. When it cools, electrons reattach to nuclei through recombination, turning plasma back into a gas.

We see plasma in neon signs, lightning, and the Sun, and it makes up over 99% of visible matter in the universe. It’s also used in technologies like plasma TVs and fusion research.

Bose-Einstein Condensate: The Super-Cold State

At temperatures near absolute zero (-273.15 K or 0 °C), some atoms slow down so much that they merge into one quantum state, behaving like a single “super atom.” This is a Bose-Einstein condensate (BEC).BECs are mostly used in research to study quantum behaviour.

A Growing List

Scientists continue to discover new and exotic states of matter. Some of these include:

• Superfluids – liquids that flow without any friction
• Fermionic condensates – similar to BECs, but made of particles that follow different quantum rules
• Quark-gluon plasma – thought to have existed just after the Big Bang
• Photonic matter – made of light behaving like particles with mass

The world of matter is far more complex and fascinating than it might first seem. As we develop better tools and technology, we continue to uncover new forms of matter that expand our understanding of the universe.

Composition of Matter

Now that we’ve explored how matter can exist in different states, let’s take a closer look at what matter is made of. As previously discussed, all matter is made up of tiny particles—atoms, molecules, or ions. Sometimes these particles are all the same, and sometimes they’re joined together in specific combinations.

This brings us to the composition of matter: the types and amounts of atoms or molecules that make up a substance. What kinds of atoms and molecules are present? Is the substance made of only one kind of atom, like oxygen gas? Is it made of different atoms chemically bonded together, like in water? Or is it a physical mix of substances, like salt dissolved in water?

To organize all these possibilities, chemists classify matter into two main categories: pure substances and mixtures.

A summary of the compositions of matter. All matter is made of pure substances or mixtures. Elements are the simplest substances and can combine to form compounds. Compounds and elements can also mix to form mixtures. By combining or separating substances, different compositions of matter can be created.

Pure Substances

A pure substance has a constant, uniform composition. That means no matter where you get a sample—from a lab, a grocery store, or the middle of the ocean—it will have the same makeup and the same properties. Pure substances always behave in predictable ways.

Pure substances come in two types: elements and compounds.

Elements

An element is a substance made of only one kind of atom, the smallest particle of an element. Some elements exist in nature as individual atoms, such as neon (Ne) and argon (Ar). Others are found as molecules, where two or more of the same atom are chemically bonded together. These are called molecular elements. Examples of molecular elements: include nitrogen (N₂), oxygen (O₂), iodine (I₂), and bromine (Br₂).

Elements. Helium (He) is an example of an element that exists as individual atoms (monoatomic). H₂, O₂, Cl₂, O₃, and S₈ are examples of molecular elements, where atoms of the same element are bonded together.

All known elements are listed in the periodic table, which organizes them based on their properties. There are 118 known elements so far—some natural, some man-made.

Compounds

A compound is a pure substance made from two or more different elements that are chemically bonded together. These elements always combine in a fixed ratio, and the resulting compound has unique properties that are often very different from the elements it came from.

Let’s take table salt (sodium chloride, NaCl) as an example. Sodium (Na) is a soft, silvery metal that reacts explosively with water, while chlorine (Cl₂) is a greenish-yellow gas that’s poisonous to breathe. But when combined chemically, they form NaCl—a harmless, white crystalline solid used to flavor food. Other examples of compounds include water (H₂O), ammonia (NH₃) and carbon dioxide (CO₂), and methane (CH₄).

Compounds. Unlike elements, compounds are made of more than one type of atom. However, they still have a fixed composition, and—like molecular elements—the atoms in a compound are chemically bonded.

Some compounds are made of molecules, like water and sugar, where atoms are bonded together in small groups. Others, like NaCl, are made of ions—electrically charged atoms or groups of atoms held together in a repeating structure.

One key thing about compounds: they always have the same composition by mass. For example, water is always about 11.1% hydrogen and 88.9% oxygen by mass. This rule is known as the law of definite proportions (or the law of constant composition). No matter where you get your water from, this ratio won’t change.

That’s different from mixtures, where the composition can vary. For example, a mixture of iron and sulfur still contains little pieces of iron and bits of yellow sulfur—you can vary the amounts. However, in the compound iron pyrite (FeS₂), iron and sulfur are chemically bonded in a fixed ratio. It’s a shiny gold-colored mineral (sometimes called “fool’s gold”) that looks and behaves nothing like either iron or sulfur.

Mixtures

Most of the stuff we see around us every day isn’t pure—it’s a mixture. A mixture is made of two or more substances physically combined, meaning each part keeps its own identity. You can often separate mixtures using simple physical methods like filtering, sifting, or evaporation.

Unlike pure substances, mixtures don’t have a fixed formula. The amount of each part can vary depending on how it’s made.

There are two main types of mixtures: homogeneous and heterogeneous.

Homogeneous vs heterogeneous mixtures. Homogeneous mixtures look the same throughout—you can’t see the individual components. Heterogeneous mixtures have visibly different parts, and their components may settle or separate over time.

Homogeneous Mixtures

A homogeneous mixture, also called a solution, looks completely uniform throughout. You can’t see any separate parts, and everything stays mixed evenly over time. The particles are so tiny you can’t even see them under a microscope, and they won’t get caught by a filter. These mixtures usually look clear.

An example of this is salt water—salt dissolved in water forms a clear, stable solution. You can’t see or filter out the salt once it dissolves. Sports drinks are another example as water, sugar, electrolytes, and flavoring all mix into one uniform liquid. Air is also a homogenous mixture of nitrogen, oxygen, and other gases that looks and feels the same no matter where you breathe it.

Heterogeneous Mixtures

A heterogeneous mixture is the opposite—they do not have a uniform composition, and its different components are distinguishable. The substances aren’t spread out evenly, and they might separate if left to sit.

Think of a chocolate chip cookie. You can spot the chips, the dough, maybe even some nuts—each part stands out. Or a slab of granite, where you can see crystals of different minerals. Even soda can be heterogeneous—when freshly opened, it contains visible bubbles of carbon dioxide gas dispersed in the liquid.

Heterogeneous mixtures can be grouped into two types based on particle size and how the mixture behaves: suspensions and colloids.

A suspension is a mixture with large particles that temporarily stay mixed, but eventually settle out when left alone. Particles often sink to the bottom or float to the top. You can observe this by stirring a handful of sand into a glass of water. At first, the water looks cloudy. But after a while, the sand sinks to the bottom.

Water and sand suspension. When sand is mixed with water, the mixture looks cloudy at first. But if left undisturbed, the sand settles to the bottom. This settling over time is a key characteristic of a suspension.

Suspensions may look cloudy, and you can separate the particles using a filter. Some liquid medicines are suspensions too—that’s why the bottle says “shake well before use.”

A colloid is a mixture with medium-sized particles—not as tiny as those in a solution, but not as big as in a suspension. Colloids may look uniform at first glance, but they’re still heterogeneous when viewed more closely.

The particles in a colloid don’t settle out and can’t be filtered, but they do scatter light. This is known as the Tyndall effect. That’s why a beam of headlights looks visible in fog or mist. Aside from fog, milk, gelatin, and shaving cream are also examples of colloids.

Solutions, suspensions, and colloids. Solutions are homogeneous mixtures with particles too small to scatter light. Hence, it exhibits no Tyndall effect. Suspensions and colloids are heterogeneous. Suspensions have large particles that scatter light and settle over time. Colloids have medium particles that stay mixed and show the Tyndall effect without settling.

The characteristics of solutions, suspensions, and colloids and summarized in the table below.

Mixture Type	Looks Like	Particle Size	Settles Out?	Can Be Filtered?	Scatters Light?
Solution	Clear, uniform	Very small	No	No	No
Colloid	Cloudy, uniform	Medium	No	No	Yes (Tyndall effect)
Suspension	Cloudy, separates	Large	Yes	Yes	Sometimes

So, understanding the composition of matter goes beyond just knowing what something is made of—it’s about recognizing how substances are combined and how we can tell them apart. Whether a substance is pure or part of a mixture, whether it’s evenly mixed or not, helps us predict how it will behave and how we might separate or use it. This knowledge helps scientists, chefs, engineers, and even artists decide how to use materials in their respective fields.

Now that we’ve explored how matter is classified by its state and composition, we’re ready to look deeper at what makes each type of matter unique. In the next section, we’ll explore their physical and chemical properties, and how those affect physical and chemical changes.

Properties of Matter and How It Changes

Every piece of matter—whether it’s water, a metal spoon, or a scoop of cookie dough—has certain traits that help us understand what it is and how it behaves. Scientists call these traits properties, and they tell us a lot about how matter acts, especially when it changes.

When we talk about how matter behaves or transforms, we usually break things down into two main types: physical and chemical properties and changes. In this section, we’ll explore what these mean and how they help us make sense of the world.

Physical Properties and Changes

Physical properties are traits you can observe or measure without changing the identity of the material. This means the composition stays the same, even if the appearance or state changes.

Physical properties can either be intensive or extensive depending on whether they are influenced by the amount of material present. Intensive properties do not depend on the amount of the substance. They’re useful for identifying substances because they stay the same even if the sample size changes. Examples include:

• Color – Copper is reddish; sulfur is yellow.
• Density – Water has a density of 0.998 g/cm³ at 25°C; corn oil is less dense
• Melting/Boiling point – Gallium melts at 30°C; water boils at 100°C.
• Hardness – Diamond is hard; graphite is soft, even though both are carbon.
• Solubility – Salt easily dissolves in water.
• Electrical conductivity – Silver conducts electricity well.
• Malleability and ductility – Silver can be shaped into sheets or wires.

On the other hand, extensive properties depend on the amount of material present—if you double the amount, these properties double too. Examples include:

• Mass – A bag of flour has more mass than a teaspoon.
• Volume – A liter of milk takes up more space than a cup.
• Length – A longer copper wire has more material than a shorter one.
• Heat capacity – A bigger sample can store more heat.

Examples of intensive and extensive properties. Intensive properties do not depend on the amount of matter while extensive properties do.

Likewise, a physical change happens when matter changes its appearance but not its identity. Nothing new is created at the atomic level. All phase changes are physical changes—water, for instance, is still composed of H₂O molecules whether it melts, freezes, or evaporates. Cutting or reshaping materials, like tearing paper or molding clay, is also an example of a physical change.

Examples of physical changes. A physical change doesn’t produce a new substance—it only affects the form or appearance, not the identity, of the material.

Dissolving compounds like NaCl is also a physical change. When salt dissolves in water, the salt breaks into ions that are surrounded by water molecules, but they’re still sodium and chloride ions. No new substance is formed. As with most physical changes, this process is reversible—you can get the salt back by evaporating the water just as you can freeze water after it melts. 

Chemical Properties and Changes

While physical properties describe what a substance is like, chemical properties describe how it behaves when it interacts with other substances. These are traits that become obvious only when a chemical change happens—that is, the composition of a substance changes as it forms one or more new substances with new properties.

Some examples of chemical properties include:

• Flammability – Hydrogen gas can explode if exposed to a flame.
• Reactivity with acids – Zinc fizzes and gives off gas when dropped into hydrochloric acid.
• Corrosion – Iron rusts when exposed to oxygen and water.
• Decomposition – Some substances break down over time or with heat.

Examples of chemical properties. Chemical properties can only be observed when a substance undergoes a chemical change, which involves the breaking and forming of chemical bonds to produce new substances.

The chemical changes associated with these chemical properties often come with at least one of following observations:

1. Unexpected Color Change – When iron rusts, it turns from a shiny gray metal to a flaky orange-brown rust (iron oxide).
2. Temperature Change – Cooking an egg absorbs heat, and new proteins form as the egg solidifies.
3. Production of Gas – Adding zinc to hydrochloric acid produces bubbles of hydrogen gas.
4. Formation of a Precipitate – Mixing solutions of silver nitrate and sodium chloride forms a white solid (silver chloride) that settles out of solution.
5. Change in Odor or Taste – spoiled milk develops a sour smell due to the formation of lactic acid.
6. Light or Flame Produced – A candle burning produces both heat and light as wax reacts with oxygen to form carbon dioxide and water.

Signs of a chemical change. These observations often suggest a chemical reaction has occurred—but not always. Some physical changes can look similar.

While some chemical changes can be reversed under specific conditions, most are not easily undone. For example, you can’t un-boil an egg or turn rust back into iron without complex chemical processing.

Note that just because these are observed does not always mean that a reaction occurred. Heating water changes its temperature without changing its composition, and mixing water with different food coloring results in a color change but does not produce any new substances.

We’ve just explored how matter changes—through physical changes like melting or dissolving, and chemical changes like rusting or burning. But these changes don’t happen on their own—every physical and chemical change involves energy.

As you may recall, the definition of chemistry includes not just the study of matter, but also the energy involved in its changes. So to fully understand chemical reactions, we need to understand the role energy plays.

The Role of Energy in Chemistry

Energy is the capacity to do work or produce heat. In chemistry, energy is involved whenever matter changes—physically or chemically. Whether water is boiling, a metal is rusting, or fuel is burning, some form of energy is being absorbed or released.

Forms of Energy

Chemistry involves many forms of energy, but they can all be grouped into two main types: kinetic energy and potential energy.

Kinetic Energy — Energy of Motion

Kinetic energy is the energy of moving objects or particles. The faster something moves, the more kinetic energy it has. Examples include:

• Thermal energy – the motion of atoms and molecules; increases with temperature
• Mechanical energy – motion of visible objects
• Electrical energy – flow of electrons
• Acoustic energy – vibration of particles as sound waves

Potential Energy — Stored Energy

Potential energy is energy stored due to an object’s position, structure, or condition. This includes:

• Chemical energy – stored in bonds between atoms in molecules
• Gravitational energy – stored in an object held at a height
• Electrostatic energy – stored due to the separation of charges
• Elastic energy – stored in stretched or compressed materials

The Law of Conservation of Energy

Whether a change is physical or chemical, energy is never created or destroyed—it only changes form. This principle is known as the law of conservation of energy. Let’s explore how this applies in different types of changes.

Energy in Physical Changes

In a physical change, the chemical identity of the substance stays the same, but energy is still transformed. For example:

• Phase changes (e.g., melting, boiling): Heat is absorbed or released, and particles move faster or slower as potential energy is converted to thermal energy or vice versa. 
• Stretching a spring: Elastic potential energy is converted into mechanical energy when it snaps back.
• Lighting a bulb: Electrical energy is converted into radiant and thermal energy, producing light and heat without changing the substance.

Examples of energy transformations in physical changes. Energy transformations occur without changing the identity of the substance.

Energy in Chemical Changes

Chemical changes involve breaking old bonds and forming new ones, which always involves energy transformations. Examples include:

• Burning wood: Chemical energy is released as heat and light in a combustion reaction.
• Photosynthesis: Light energy from the sun is stored as chemical energy in glucose molecules.
• Metabolism: The body breaks down food molecules, converting chemical energy into thermal and kinetic energy for body functions and movement.

Examples of energy transformations in chemical changes. Energy transformations occur with the formation of new substances.

Conclusion: From Stardust to You

Everything you’ve learned in this chapter points back to one powerful idea: you—and everything around you—are made of matter. And that matter is constantly changing, powered by energy.

We explored what matter is, how to classify it by state and composition, and how to describe its properties. You also learned to tell the difference between physical changes—like melting or dissolving—and chemical changes that create entirely new substances, along with the energy that drives those changes.

Understanding these basics is like learning the alphabet of chemistry. It gives you the tools to recognize the transformations happening all around you, every day. From the formation of stars to the fizz of a soda, chemistry is the science that helps us make sense of change.

And it all starts with matter—what it is, how it behaves, and what it can become.

This is more than just a science class. It’s your first step in understanding how the universe is built—one atom at a time.