States of matter

The four main states of matter: solid, liquid, plasma, and gas.

In a gas, molecules are far apart and move freely.

Everything around us is made of matter. Matter can exist in different forms, called states of matter or phases. The four most common states we see are solids, liquids, gases, and plasma. How matter behaves depends on its state. For example, a solid is hard, but a liquid can flow. The state of matter affects things like how dense something is or how easily it can be bent.

Common States of Matter

What are Solids?

This image shows atoms in a solid material. They are arranged in a very neat pattern.

In a solid, the tiny particles (like atoms or molecules) are packed very closely together. They are held in fixed positions by strong forces, like tiny invisible glue. This means solids keep their own shape. They don't spread out like liquids or gases. Think of a rock or a block of ice. Solids are usually very dense.

What are Liquids?

Liquid helium can creep up the sides of a cup.

In a liquid, the particles are still close together, but they are not held in fixed spots. They can slide and move past each other. This is why liquids can flow! A liquid will take the shape of any container you put it in. Water, juice, and oil are all liquids. Liquids are usually less dense than solids.

What are Gases?

This shows how gas particles move when they are cooled down.

In a gas, the particles are very far apart from each other. They move around freely and quickly, bumping into each other and the sides of their container. The forces holding them together are very weak. Gases will spread out to fill any container they are in. Air is a mixture of different gases. Gases are much less dense than liquids or solids.

What is Plasma?

In plasma, electrons are separated from their atoms. This lets electricity flow easily.

Plasma is like a super-energetic gas. It forms when a gas gets so hot that its atoms break apart. The electrons (tiny negatively charged particles) get ripped away from the atomic nuclei (the center of the atom). This creates a mix of charged particles.

Because plasma has these free charged particles, it can conduct electricity very well. Lightning is an example of plasma in action. The air gets so much energy that it turns into plasma for a short time, allowing electricity to flow. Plasma is the most common state of matter in the whole universe. Stars, like our Sun, are mostly made of plasma!

How Matter Changes States

This diagram shows how matter can change from one state to another.

Matter can change from one state to another. These changes are often caused by changes in temperature or pressure.

• When a solid turns into a liquid, it's called melting. (Think of ice melting into water.)
• When a liquid turns into a solid, it's called freezing. (Think of water freezing into ice.)
• When a liquid turns into a gas, it's called evaporation or boiling. (Think of water turning into steam.)
• When a gas turns into a liquid, it's called condensation. (Think of water droplets forming on a cold glass.)
• When a solid turns directly into a gas (without becoming a liquid first), it's called sublimation. (Dry ice does this.)
• When a gas turns directly into a solid, it's called deposition. (Frost forming on a cold window is an example.)

The temperature where a substance melts is the same temperature where it freezes. For example, water melts and freezes at 0 degrees Celsius (32 degrees Fahrenheit).

Other Cool States of Matter

Scientists are always discovering and studying other special states of matter. These often happen under extreme conditions, like super cold temperatures or super high pressures.

Quark-Gluon Plasmas

Quark-gluon plasmas are a very new and exciting state of matter. They form at incredibly high temperatures, about 2 trillion degrees Kelvin! Scientists believe that tiny particles called quarks and gluons (which usually make up protons and neutrons) separate into this new state. It takes a huge amount of energy to create them, like in the Large Hadron Collider at CERN.

Bose-Einstein Condensates

Bose-Einstein condensates are states of matter that form at incredibly low temperatures, almost as cold as possible (about -452 degrees Fahrenheit!). In this state, a group of particles called bosons start to act like one big "super-particle." They have almost no electrical resistance and very little friction. Scientists are still learning a lot about these strange and wonderful states.

See also

In Spanish: Estado de agregación de la materia para niños