2.2. Classification of Matter http://www.ck12.org
States of Matter
Matter typically exists in one of three states: solid, liquid, or gas. The state of a given substance is a physical
property. Some substances exist as gases at room temperature (such as 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.
Water is a very common substance that we frequently encounter in all three states of matter, as seen inFigure2.2.
When water is in the solid state, we call it ice, while water in the gaseous state is referred to as steam or water vapor.
The physical state of matter is a physical property because the identity of apure substancedoes not change when it
is melted, frozen, or boiled.
FIGURE 2.2
Water is the same substance in any of
its three states. (A) A frozen waterfall in
Hungary. (B) The Nile River in Egypt. (C)
A steam powered train in Wales.Solid
A solid is a form of matter that has a definite shape and volume. The shape of a solid does not change if it is
transferred from one container to another. The particles of a solid are packed tightly together in fixed positions,
usually in an orderly arrangement. Solids are almost completely incompressible, meaning that solids cannot be
squeezed into a smaller volume. When a solid is heated or cooled, it expands or contracts only slightly.
Liquid
A liquid is a form of matter that has a definite volume, but an indefinite shape. As water is poured from one container
into another, it adopts the shape of its new container. However, the volume of the water does not change, because
the water molecules are still relatively close to one another in the liquid state. Unlike a solid, the arrangement of
particles in a liquid is not rigid and orderly. Liquids are also incompressible.
Gas
A gas is a form of matter that has neither a definite shape nor a definite volume. A gas takes up the shape and volume
of its container. This is because the particles of a gas are very far apart from one another compared to the particles
that make up solids and liquids. Gases are easily compressed because of the large spaces in between gas particles.
Gas particles are often invisible, but they can be detected in various ways, such as the light emitted when an electric
current is passed through a sample of a gas (Figure2.3).
Molecular View of Solids, Liquids, and Gases
We are quite familiar with the properties of solids, liquids, and gases from our everyday experience. These properties
are fundamentally based on differences in the arrangement of atoms or molecules at the microscopic level.Figure