Learning Outcomes List the three states of matter and give examples of each. Describe the properties of each state of matter. Identify and describe each type of change in state. States of Matter Under normal conditions, there are three distinct states of matter: solids, liquids, and gases. Solids are relatively rigid and have fixed shapes and volumes. A rock, for example, is a solid. In contrast, liquids have fixed volumes but flow to assume the shape of their containers, such as a beverage in a can. Gases , such as air in an automobile tire, have neither fixed shapes nor fixed volumes and expand to completely fill their containers. Whereas the volume of gases strongly depends on their temperature and pressure (the amount of force exerted on a given area), the volumes of liquids and solids are virtually independent of temperature and pressure. Matter can often change from one physical state to another in a process called a physical change . For example, liquid water can be heated to form a gas called steam, or steam can be cooled to form liquid water. However, such changes of state do not affect the chemical composition of the substance. The state of a substance depends on the balance between the kinetic energy of the individual particles (molecules or atoms) and the intermolecular forces . The kinetic energy keeps the molecules apart and moving around, and is a function of the temperature of the substance. The intermolecular forces are attractive forces that try to draw the particles together (Figure 2). Gasses are very sensitive to temperatures and pressure. However, these also affect liquids and solids too. Heating and cooling can change the kinetic energy of the particles in a substance, and so, we can change the physical state of a substance by heating or cooling it. Increasing the pressure on a substance forces the molecules closer together, which increases the strength of intermolecular forces. Unnamed: 0 Gas Liquid Solid Shape no definite shape (takes the shape of its container) no definite shape (takes the shape of its container) definite shape (rigid) Volume particles move in random motion with little or no attraction to each other has definite volume definite volume Mobility particles move in random motion with little or no attraction to each other particles are free to move over each other, but are still attracted to each other particles vibrate around fixed axes Compressibility highly compressible weakly compressible weakly compressible 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. Changing States Matter constantly goes through cycles that involve changing states (also called change phases). Water and all the elements important to organisms, including carbon and nitrogen, are constantly recycled on Earth. As matter moves through its cycles, it changes state repeatedly. For example, in the water cycle, water repeatedly changes from a gas to a liquid or solid and back to a gas again. How does this happen? Adding energy to matter gives its atoms or molecules the ability to resist some of the forces holding them together. For example, heating ice to its melting point gives its molecules enough energy to move. The ice melts and becomes liquid water. Similarly, heating liquid water to its boiling point gives its molecules enough energy to pull apart from one another so they no longer have contact. The liquid water vaporizes and becomes water vapor. The temperature of the melting and boiling points depend on the identity of the substance and the atmospheric pressure. Each substance has its own boiling and melting points that depend on the properties of the substance, including the strength of its intermolecular forces. Key Takeaway 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 their container. Gases have no definite shape or volume.