# 2.4: Solid, Liquid, and Gas

Water can take many forms. At low temperatures (below $$0^\text{o} \text{C}$$), it is a solid. When at "normal" temperatures (between $$0^\text{o} \text{C}$$ and $$100^\text{o} \text{C}$$), it is a liquid. While at temperatures above $$100^\text{o} \text{C}$$, water is a gas (steam). The state the water is in depends upon the temperature. Each state (solid, liquid, and gas) has its own unique set of physical properties.

### Matter and Its States

Matter typically exists in one of three states: solidliquid, or gas. The state a given substance exhibits is also a physical property. Some substances exist as gases at room temperature (oxygen and carbon dioxide), while others, like water and mercury metal, exist as liquids. Most metals exist as solids at room temperature. All substances can exist in any of these three states.

Figure $$\PageIndex{1}$$: Matter is usually classified into three classical states, with plasma sometimes added as a fourth state. From top to bottom: quartz (solid), water (liquid), nitrogen dioxide (gas),

Note

Technically speaking a fourth state of matter called plasma exists, but it does not naturally occur on earth, so we will omit it from our study here.

#### Solid

Solids are defined by the following characteristics:

• Definite shape (rigid)
• Definite volume
• Particles vibrate around fixed axes

If we were to cool liquid mercury to its freezing point of $$-39^\text{o} \text{C}$$, and under the right pressure conditions, we would notice all of the liquid particles would go into the solid state. Mercury can be solidified when its temperature is brought to its freezing point. However, when returned to room temperature conditions, mercury does not exist in solid state for long, and returns back to its more common liquid form.

#### Liquid

Liquids have the following characteristics:

• No definite shape (takes the shape of its container)
• Has definite volume
• Particles are free to move over each other, but are still attracted to each other

A familiar liquid is mercury metal. Mercury is an anomaly. It is the only metal we know of that is liquid at room temperature. Mercury also has an ability to stick to itself (surface tension) - a property all liquids exhibit. Mercury has a relatively high surface tension, which makes it very unique. Here you see mercury in its common liquid form.

Mercury.

If we heat liquid mercury to its boiling point of $$357^\text{o} \text{C}$$, and under the right pressure conditions, we would notice all particles in the liquid state go into the gas state.

#### Gas

Gases have the following characteristics:

• No definite shape (takes the shape of its container)
• No definite volume
• Particles move in random motion with little or no attraction to each other
• Highly compressible

### Summary

Three states of matter exist - solid, liquid, and gas. Solids have a definite shape and volume. Liquids have a definite volume, but take the shape of the container. Gases have no definite shape or volume

### Contributors

• CK-12 Foundation by Sharon Bewick, Richard Parsons, Therese Forsythe, Shonna Robinson, and Jean Dupon.