States of matter. Theory and practice with simulations

07/05/2026

The online simulations of states of matter on this page help us to visualize the behavior of matter at the molecular level in each of the three physical states of matter. We will discover the three classical physical states of matter, which are the solid state, the liquid state and the gaseous state, and we will also learn about the fourth physical state of matter: plasma

This Thematic Unit is part of our Chemistry collection

Boiling point

Temperature at which the vapor pressure of a liquid equals the external pressure, causing the transition to the gaseous state.

Critical Point

Conditions of pressure and temperature above which the liquid and gaseous phases of a substance are indistinguishable.

Melting point

Temperature at which a substance changes from solid to liquid state at a given pressure.

Plasma

Ionized gas at high temperatures composed of free electrons and positive ions, capable of conducting electricity.

States of Matter

Forms of aggregation in which matter exists (solid, liquid, gas, and plasma) depending on the intensity of cohesive forces.

Sublimation

Phase change in which a solid substance passes directly to the gaseous state without passing through the liquid state.

Triple Point

Specific set of pressure and temperature at which the solid, liquid, and gaseous phases of a substance coexist in equilibrium.

Vapor Pressure

Pressure exerted by the gaseous phase on the liquid phase in a closed system when both are in dynamic equilibrium.

What are the physical states of matter

The physical states of matter are the forms in which matter appears and can be classified. The most common states are solid, liquid and gas, but there are also other, less well-known states, such as plasma and the Bose-Einstein condensate.

Solid state

In the solid state, the particles that make up matter are tightly bound together and have an ordered structure. The atoms, ions or molecules in a solid are held in fixed positions and have only vibrational motions. Solids have a definite shape and volume.

Liquid state

In the liquid state, the particles have a less ordered structure and are farther apart than in the solid state. The particles can move freely, although they are still in contact with each other. Liquids have a defined volume, but do not have a defined shape and take the shape of the container that holds them.

Gaseous state

In the gaseous state, the particles are widely separated and move in a disorderly and rapid manner. They have no fixed structure and occupy the entire available volume of the container in which they are found. Gases have no definite shape and expand to completely fill the available space.

Plasma

Plasma is a state of matter found at high temperatures or under high energy conditions. In plasma, the atoms are ionized, i.e., the electrons are separated from the nuclei. Plasma is highly electrically conductive and is present in phenomena such as lightning and in the interior of stars.

The Bose-Einstein condensate is an exotic state that occurs at temperatures very close to absolute zero. In this state, a large number of particles behave as if they were a single particle, giving rise to collective quantum phenomena.

Properties of the states of matter

These different states of matter have different properties and can be transformed from one to another by changes in temperature and pressure. Understanding the states of matter is fundamental to physics and chemistry, as they affect many properties and processes in our everyday environment and in the universe in general.

Boiling point

Temperature at which the vapor pressure of a liquid equals the external pressure, causing the transition to the gaseous state.

Critical Point

Conditions of pressure and temperature above which the liquid and gaseous phases of a substance are indistinguishable.

Melting point

Temperature at which a substance changes from solid to liquid state at a given pressure.

Plasma

Ionized gas at high temperatures composed of free electrons and positive ions, capable of conducting electricity.

States of Matter

Forms of aggregation in which matter exists (solid, liquid, gas, and plasma) depending on the intensity of cohesive forces.

Sublimation

Phase change in which a solid substance passes directly to the gaseous state without passing through the liquid state.

Triple Point

Specific set of pressure and temperature at which the solid, liquid, and gaseous phases of a substance coexist in equilibrium.

Vapor Pressure

Pressure exerted by the gaseous phase on the liquid phase in a closed system when both are in dynamic equilibrium.

Explore the exciting STEM world with our free, online, simulations and accompanying companion courses! With them you’ll be able to experience and learn hands-on. Take this opportunity to immerse yourself in virtual experiences while advancing your education – awaken your scientific curiosity and discover all that the STEM world has to offer!

Simulations of states of matter

States of Matter I

Look at the different types of molecules that make up a solid, liquid, or gas. Add or remove heat and see the phase change. Change the temperature or volume of a container and see a pressure-temperature diagram change in real time. Relate the interaction potential of forces between molecules.

States of Matter II

Observe in this simulation how molecules interact in a solid, a liquid and a gas.

Triple point

The triple point of matter is the condition in which a substance can exist simultaneously as a solid, liquid and gas in equilibrium. It occurs at a specific temperature and pressure. This simulation allows you to place yourself at different points on the graph and check what the state of matter is. Have you found the triple point?

Giants of science

“If I have seen further, it is by standing on the shoulders of giants”

Isaac Newton

Robert Boyle

1627

–

1691

Robert Boyle formulated the first quantitative law of gases, showing the relationship between pressure and volume, laying foundations of modern chemistry and fluid mechanics

“Air is as necessary to life as food”

Edme Mariotte

1620

–

1684

Edme Mariotte independently described the relationship between gas pressure and volume, known as Boyle-Mariotte’s law, contributing to the quantitative study of fluids

“Nature never acts in vain”

Become a giant

Your path to becoming a giant of knowledge begins with these top free courses

Free mode

Thermodynamics and Phase Equilibria

Free mode

Thermodynamics

Free mode

Entropy and Equilibria

Free mode

Energy and Thermodynamics

Free mode

Big Bang and the Origin of Chemical Elements

Free mode

Preparing for CLEP Chemistry: Part 1

Free mode

Pre-University Chemistry

Professional development for Educators

Your path to becoming a giant of knowledge begins with these top free courses

Free mode

STEM Outside

Free mode

Teaching with Physical Computing: Introduction to Project-Based Learning

Free mode

BlendedX: Blended Learning with edX

Free mode

Teach teens computing: Cybersecurity

Giants of science

“If I have seen further, it is by standing on the shoulders of giants”

Isaac Newton

Joseph Louis Gay-Lussac

1778

–

1850

Joseph Louis Gay-Lussac formulated fundamental gas laws on the relationship between volume, temperature, and pressure, also studying gas mixtures and chemical reactions in air

“Chemistry is the key to understanding nature”

Gilbert Newton Lewis

1875

–

1946

Gilbert Lewis formulated the chemical bond theory, introduced electron pairs, and contributed to acid-base theory

“Atoms build nature as bricks build a building”

Become a giant

Your path to becoming a giant of knowledge begins with these top free courses

Free mode

Thermodynamics and Phase Equilibria

Free mode

Thermodynamics

Free mode

Entropy and Equilibria

Free mode

Energy and Thermodynamics

Free mode

Pre-University Chemistry

Free mode

Preparing for CLEP Chemistry: Part 1

Free mode

Big Bang and the Origin of Chemical Elements

Professional development for Educators

Your path to becoming a giant of knowledge begins with these top free courses

Free mode

AI for Teacher Assistance

Free mode

Teach teens computing: Encryption and cryptography

Free mode

Teach kids computing: Developing your programming pedagogy

Free mode

Teach kids computing: Computing systems and networks

Test your knowledge

What fundamental criteria are used to distinguish one state of matter from another, and how does energy determine these differences?

The states of matter are defined by how particles are arranged and how much energy they possess. In solids, particles are tightly packed and can only vibrate; in liquids, they have enough energy to move around each other; and in gases, they move freely and spread out to fill all available space. Energy is the key factor that drives these differences: adding energy increases particle motion and separation, while removing energy brings particles closer together and restricts their movement. This energy‑structure relationship explains why matter can transition from one state to another and why each state exhibits distinct physical properties.

How do intermolecular forces shape the macroscopic behavior of solids, liquids, and gases?

Intermolecular forces determine how strongly particles attract each other. In solids, these forces are strong enough to maintain a rigid, fixed structure. In liquids, the forces are still present but weaker, allowing particles to slide past one another and giving liquids their fluidity. In gases, the forces are so weak that particles move independently and tend to expand. These microscopic interactions explain observable properties such as shape, volume, compressibility, and density. Understanding these forces provides a clear link between particle‑level behavior and the physical characteristics we observe in everyday materials.

Why does a solid keep its shape while a liquid just takes the shape of whatever container it’s in?

Because in a solid the particles are held so tightly together that they can only vibrate in place, which keeps the shape fixed. In a liquid, the particles have more freedom and can slide around each other, so the substance can flow and adapt to the container while still keeping a definite volume.

What happens if you heat a liquid far beyond its boiling point—does it “disappear”?

It doesn’t disappear; it simply becomes a gas. When a liquid is heated, its particles gain enough energy to break free from each other and move independently. That transition is what we call vaporization. If you keep adding energy, the gas expands even more, but the matter is still there—just in a different state with much more particle motion.

How come a tiny amount of gas can spread out and fill an entire room?

Because gas particles move in all directions and barely feel any attraction to one another. As soon as they have space, they spread out until they occupy the whole volume available. They don’t need to push each other outward—each particle’s natural motion is enough to make the gas expand and fill the space. That’s why smells travel quickly or why steam fills a bathroom almost instantly.