States of matter

Picture yourself blowing bubbles by the seaside. Do you see matter in this scene? The three most common forms, or states, of matter on Earth are solids, liquids, and gases. The bubbles you blow hold air, which is a mixture of gases. The soap mixture used to make the bubbles and the ocean water are liquids. The sand, your shoes, and nearby seashells are a few of the solids you might see by the seaside.

The Fourth State of Matter

Plasma, often called the fourth state of matter, is a high-energy matter where electrons have been stripped from atoms. This superheated state constitutes over 99% of the visible universe, manifesting in various celestial phenomena. Stars, nebulae, and auroras are all forms of plasma. On Earth, we observe plasma in lightning strikes and neon signs. Our sun, the source of life on Earth, is essentially a massive sphere of plasma.

The transition to plasma occurs when sufficient energy is added to a gas, causing electron-ion separation. This process is comparable to other phase transitions but occurs at much higher energy levels. Plasma’s unique properties, particularly its responsiveness to electromagnetic fields, make it a subject of intense scientific study across multiple disciplines.

Particles in Motion

Have you ever wondered what makes something a solid, a liquid, or a gas? Two main factors that determine the state of matter are particle motion and particle forces. Atoms, ions, or molecules make up all matter. These particles can move in different ways. In some matter, they are close together and vibrate back and forth. In other matter, the particles are farther apart. Sometimes, they slide past each other. At other times, they move freely and spread out. It does not matter how close the particles are to each other. All particles have random motion. Random motion is movement in all directions and at different speeds. If particles are free to move, they move in straight lines until they collide with something. Collisions usually change the speed and direction of the particles’ movements.

Recall that atoms that make up matter have positively charged protons and negatively charged electrons. These opposite charges attract each other. They create attractive forces between any two particles. Attractive forces pull particles together. Strong attractive forces hold slow-moving particles close together, as shown in the figure below. As the motion of particles gets faster, particles move farther apart. When they get farther apart, the attractive forces between particles have a weaker effect. The spaces between them increase. This bigger space lets other particles slip past. As the motion of particles gets even faster, particles move even farther apart. In time, the distance between particles is so great that there is little or no attractive force between them. The particles move randomly and spread out.

Solids

If a skateboard moves from one place to another, its shape and volume do not change. A skateboard’s shape and volume do not change because a skateboard is a solid. A solid is matter that has a definite shape and a definite volume.

Why doesn’t a solid change shape or volume? Remember that the particles in a solid are close together. The particles are touching neighboring particles. The attractive forces between them are strong. Their strong attractive forces and slow motion hold the particles tightly in their positions. The particles still move, but they do not get away from each other. They simply vibrate back and forth in place. This arrangement gives solids a definite shape and volume.

All solids are not the same. For example, a diamond and a piece of charcoal do not look alike. However, they are both solids made of carbon atoms. They both have particles that strongly attract each other and vibrate in place. What makes them different is the arrangement of their particles. A diamond is a crystalline solid. It has particles arranged in a specific, repeating order. Charcoal is an amorphous solid. It has particles that are arranged randomly. Different particle arrangements give these materials different properties. For example, a diamond is a hard material. Charcoal is brittle.

Liquids

Have you ever seen a waterfall flowing into a riverbed? Water is a liquid. A liquid is matter with a definite volume but no definite shape. Liquids flow and can take the shape of their containers. Water from a waterfall takes the shape of the riverbed that it fills.

How can liquids change shape? The particle motion in liquids is faster than the particle motion in solids. This faster motion causes the particles to move slightly farther apart. As they move farther apart, the effect of the attractive forces between them decreases. The faster motion also causes gaps to form between the particles. The gaps allow particles to slip past each other. The slightly weaker attractive forces and gaps between particles let liquids flow and take the shape of their containers.

Gases

A gas is matter that has no definite volume and no definite shape. Air is all around us all the time. Air is a mixture of gases, including nitrogen, oxygen, argon, and carbon dioxide.

Why don’t gases have definite volumes or definite shapes? Compared to the particles in the solid and the liquid states, the particles in gases are very far apart. The distances between the particles in a solid are small. The particles touch each other. The distances between the particles in a liquid are greater, and the particles can slip past each other. The distances between the particles in a gas differ from those in solids and liquids. In a gas, the forces of attraction between the particles are not strong enough to keep the particles close together. As a result, distances between particles are greater in the gas state.