Everything you have ever touched, breathed or drunk is matter, and every bit of it exists in one of a small number of forms that scientists call states of matter. Ice in a cold drink, the drink itself and the air above the glass are all the same kind of stuff behaving in completely different ways. Knowing why is the first step toward understanding chemistry, weather, cooking and even the stars.
This guide explains each state in plain language, shows how the same particles rearrange to become every state, and answers the questions people most often ask about them.
What Is Matter?
Matter is anything that has mass and takes up space. Your body, a pencil, the ocean and the oxygen you just inhaled are all matter. Light and heat are not, because they have no mass of their own and do not occupy space the way objects do.
Matter is built from particles far too small to see: atoms and molecules. Those particles never sit still. They vibrate, jostle and fly, and the amount of energy they carry decides how freely they can move. That single idea, particle energy, explains every state of matter.
The Four States of Matter
Everyday matter comes in four states: solid, liquid, gas and plasma. The first three are the ones you meet daily. Plasma is rare on Earth, but it is overwhelmingly common in the universe.
Solids: Packed In and Locked Down
In a solid, particles are packed tightly in a fixed, orderly pattern and can only vibrate in place. That is why a solid keeps both its shape and its volume. Push on it, and the particle grid resists instead of rearranging. Ice, rocks, wood, salt crystals and most metals are solids. A brick is a brick whether it sits on a shelf or in a wheelbarrow.
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| Particles in a solid vibrate in place but keep their positions. Image: Julio Miguel A. Enriquez & Monica Muñoz, CC BY-SA 4.0, via Wikimedia Commons |
Liquids: Close Together but Free to Slide
Add energy, and the particles begin to slip out of their fixed positions. They stay close together, which is why a liquid keeps its volume, but they can now slide past one another. That is why water pours, splashes and takes the shape of whatever holds it. Water, milk, cooking oil and the liquid mercury once used in thermometers are all liquids.
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| In a liquid, particles stay close but slide past one another. Image: Julio Miguel A. Enriquez & Monica Muñoz, CC BY-SA 4.0, via Wikimedia Commons |
Gases: Far Apart and Fast
In a gas, the particles have so much energy that they break away from each other almost completely. They fly in straight lines, collide and spread out to fill every corner of the space they are given. Gases have no fixed shape and no fixed volume. Because the particles are mostly empty space, a gas can also be squeezed into a much smaller volume, which is exactly what happens inside a bicycle pump. The oxygen and nitrogen in the air, helium in party balloons and carbon dioxide in fizzy drinks are gases.
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| In a gas, particles fly freely and fill the whole container. Image: Julio Miguel A. Enriquez & Monica Muñoz, CC BY-SA 4.0, via Wikimedia Commons |
Plasma: The Fourth State
Heat a gas far enough, and its collisions become so violent that electrons are torn off their atoms, leaving a soup of charged particles. This ionized gas is plasma, the fourth state of matter. Because it carries charge, plasma conducts electricity and responds to magnetic fields, which ordinary gases do not.
Plasma may be the state you know least, yet it is the most common one in the visible universe. The MIT Plasma Science and Fusion Center puts it at more than 99 percent of what we can see. Every star, including the Sun, is a giant ball of it. Closer to home, lightning bolts, the glowing gas inside neon signs and the arcs of welding torches are all plasma.
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| A Jacob's ladder arc: the glowing filament is plasma, an ionized, electrically conductive gas. Image: Chocolateoak, CC BY-SA 3.0, via Wikimedia Commons |
How Matter Changes State
States are not permanent. Add or remove energy, and the same substance slips from one state to another, with nothing chemically new created. Ice, liquid water and steam are all the same substance: H2O.
Melting turns a solid into a liquid, and freezing does the reverse. Vaporization, which includes boiling and everyday evaporation, turns a liquid into a gas. Condensation turns a gas back into a liquid. Sublimation skips the liquid stage entirely, which is how dry ice turns straight from solid carbon dioxide into gas. Its opposite, deposition, turns water vapor directly into the frost you find on a cold window.
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| How the states connect: every arrow is just particles gaining or losing energy. Image: Flanker & penubag, Public domain, via Wikimedia Commons |
The Four States at a Glance
| State | Shape | Volume | Particle movement | Familiar example |
| Solid | Fixed | Fixed | Vibrate in place | Ice, iron |
| Liquid | Takes its container's shape | Fixed | Slide past each other | Water, oil |
| Gas | None | None | Fast and far apart | Air, helium |
| Plasma | None | None | Charged and extremely energetic | Lightning, the Sun |
The four states compared by the two properties a reader can check for themselves: what shape and volume the substance keeps.
Key Terms in Plain English
These are the words in this article that would send you to a dictionary. Each one is given here the way it is actually used above.
| Term | What it means |
| Matter | Anything that has mass and takes up space. |
| Atom | The smallest particle of an element that still behaves as that element. |
| Molecule | Two or more atoms joined together, such as the two hydrogen atoms and one oxygen atom in water. |
| Particle energy | The energy an atom or molecule carries. It decides how freely that particle can move. |
| Solid | A state in which particles sit in a fixed pattern and only vibrate in place. |
| Liquid | A state in which particles stay close together but can slide past one another. |
| Gas | A state in which particles are far apart, move fast and fill whatever space they are given. |
| Plasma | An ionized gas, meaning its electrons have been torn from its atoms, leaving charged particles behind. |
| Ionized | Having lost or gained electrons, so the particle now carries an electric charge. |
| Vaporization | The change from liquid to gas, which includes boiling and everyday evaporation. |
| Sublimation | The change from solid straight to gas, skipping the liquid stage. Dry ice does this at room temperature. |
The words in this article that would otherwise send you to a dictionary, defined as they are used above.
Key Takeaways
- Matter is anything with mass and volume, and its state depends on how much energy its particles carry.
- Solids keep their shape, liquids keep their volume but flow, and gases fill whatever space they are given.
- Plasma is an ionized, electrically conductive gas, and it is the most common visible state of matter in the universe.
- Melting, boiling, condensing and sublimating are the same particles rearranging as energy is added or removed.
Frequently Asked Questions
Can a solid turn straight into a gas?
Yes. The change is called sublimation. Dry ice does it at room temperature, going straight from solid carbon dioxide to gas without melting first.
Is fire a plasma?
Usually not. Ordinary flames contain only a few ionized particles, far fewer than a true plasma such as lightning, so fire is generally treated as hot gas rather than plasma.
Does matter disappear when it changes state?
No. The substance is the same throughout, and only the arrangement and energy of its particles change. Ice, liquid water and steam are all H2O.
Are there more than four states?
There are more that scientists study, including Bose-Einstein condensates and the state of matter inside a neutron star. The four in this article are the ones you meet in ordinary life.
Key references
• MIT Plasma Science and Fusion Center — What is Plasma?
• U.S. Department of Energy — DOE Explains: Plasma
• NASA Scientific Visualization Studio — What is Plasma?
The figure for plasma in the visible universe (more than 99 percent) is from the MIT Plasma Science and Fusion Center. The particle model of the four states and the names of the phase changes follow standard introductory chemistry. Figures are from Wikimedia Commons under the license named in each caption.
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