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# States of Matter

## Introduction to one of the four states of matter where particles are tightly packed and have a definite shape and volume.

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States of Matter

The striking blue walls in this photo are actually the sheer ice walls of a massive glacier. The glacier in the picture is in Argentina, and the bluish water in the foreground is Lake Argentina. The photo represents an important concept in physical science. Can you guess what it is?

### Water, Water Everywhere

The photo above represents water in three common states of matter. States of matter are different phases in which any given type of matter can exist. There are actually four well-known states of matter: solid, liquid, gas, and plasma. Plasma isn’t represented in the iceberg photo, but the other three states of matter are. The iceberg itself consists of water in the solid state, and the lake consists of water in the liquid state.

Q: Where is water in the gaseous state in the above photo?

A: You can’t see the gaseous water, but it’s there. It exists as water vapor in the air.

Q: Water is one of the few substances that commonly exist on Earth in more than one state. Many other substances typically exist only in the solid, liquid, or gaseous state. Can you think of examples of matter that usually exists in just one of these three states?

A: Just look around you and you will see many examples of matter that usually exists in the solid state. They include soil, rock, wood, metal, glass, and plastic. Examples of matter that usually exist in the liquid state include cooking oil, gasoline, and mercury, which is the only metal that commonly exists as a liquid. Examples of matter that usually exists in the gaseous state include oxygen and nitrogen, which are the chief gases in Earth’s atmosphere.

### Phases Are Physical

A given kind of matter has the same chemical makeup and the same chemical properties regardless of its state. That’s because state of matter is a physical property. As a result, when matter changes state, it doesn’t become a different kind of substance. For example, water is still water whether it exists as ice, liquid water, or water vapor.

### Properties of Solids, Liquids, and Gases

The most common states of matter on Earth are solids, liquids, and gases. How do these states of matter differ? Their properties are contrasted in the Figure below. You can also watch videos about these three states of matter at the following URLs.

Properties of matter in different states.

### Snowflakes and Other Solids

A snowflake is made of ice, or water in the solid state. A solid is one of four well-known states of matter. The other three states are liquid, gas, and plasma. Compared with these other states of matter, solids have particles that are much more tightly packed together. The particles are held rigidly in place by all the other particles around them so they can’t slip past one another or move apart. This gives solids a fixed shape and a fixed volume.

### Water and Other Liquids

Water is the most common substance on Earth, and most of it exists in the liquid state. A liquid is one of four well-known states of matter, along with solid, gas, and plasma states. The particles of liquids are in close contact with each other but not as tightly packed as the particles in solids. The particles can slip past one another and take the shape of their container. However, they cannot pull apart and spread out to take the volume of their container, as particles of a gas can. If the volume of a liquid is less than the volume of its container, the top surface of the liquid will be exposed to the air, like the vinegar in the bottle pictured in the Figure below.

Q: Why does most water on Earth’s surface exist in a liquid state? In what other states does water exist on Earth?

A: Almost 97 percent of water on Earth’s surface is found as liquid salt water in the oceans. The temperature over most of Earth’s surface is above the freezing point (0°C) of water, so relatively little water exists as ice. Even near the poles, most of the water in the oceans is above the freezing point. And in very few places on Earth’s surface do temperatures reach the boiling point (100°C) of water. Although water exists in the atmosphere in a gaseous state, water vapor makes up less than 1 percent of Earth’s total water.

### What Is a Gas?

gas is one of four well-known states of matter. (The other three are solid, liquid, and plasma). The particles of a gas can pull apart from each other and spread out. As a result, a gas does not have a fixed shape or a fixed volume. In fact, a gas always spreads out to take up whatever space is available to it. If a gas is enclosed in a container, it spreads out until it has the same volume as the container.

Q: The sketches in the Figure below represent two identical sealed boxes that contain only air particles (represented by dots). There are more air particles in box B than box A. Which box contains a greater volume of air?

[Figure1]

A: This is a trick question! The air inside each box expands to fill the available space, which is identical for both boxes. There are more air particles in box B, but the volume of air is exactly the same in both boxes.

Q: The Figure below shows that a liquid takes the shape of its container. How could you demonstrate this?

A: You could put the same volume of liquid in containers with different shapes. This is illustrated below with a beaker (left) and a graduated cylinder (right). The shape of the liquid in the beaker is short and wide like the beaker, while the shape of the liquid in the graduated cylinder is tall and narrow like that container, but each container holds the same volume of liquid.

Credit: Joy Sheng, courtesy of Moerner Lab, Stanford University

[Figure2]

Q: How could you show that a gas spreads out to take the volume as well as the shape of its container?

A: You could pump air into a bicycle tire. The tire would become firm all over as air molecules spread out to take the shape of the tire and also to occupy the entire volume of the tire.

### Summary

• States of matter are different phases in which any given type of matter can exist. There are four well-known states of matter—solid, liquid, gas, and plasma—but only the first three states are common on Earth.
• State of matter is a physical property of matter. A given kind of matter has the same chemical makeup and the same chemical properties, regardless of state.
• A solid is a state of matter in which particles of matter are tightly packed together. This holds the particles rigidly in place and gives solids a fixed shape and fixed volume.
• A liquid is a state of matter in which particles can slip past one another and take the shape of their container. However, the particles cannot pull apart and spread out to take the volume of their container.
• Gas is a state of matter in which particles of matter can pull apart from each other and spread out. As a result, a gas does not have a fixed shape or a fixed volume.

### Vocabulary

• state of matter: Different phase (solid, liquid, gas, and plasma) in which matter can exist without the chemical makeup of matter changing.
• solid: State of matter that has a fixed volume and fixed shape.
• liquid: State of matter that has a fixed volume but not a fixed shape.
• gas: State of matter that has neither a fixed volume nor a fixed shape.

### Practice

Play the states of matter game at the following URL to reveal the hidden picture.

### Review

1. Define state of matter.
2. List four states of matter. Which states of matter are most common on Earth?
3. What type of property is state of matter? How could you demonstrate this?
4. Make a table comparing and contrasting solids, liquids, and gases.

### Missouri Standards

1. GLEs: None - sets the stage for changes in states of matter and kinetic theory of matter.

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