- Describe a substance according to its physical properties.
- Distinguish between extensive and intensive properties.
- Describe the three states of matter.
- Identify physical changes to matter.
- extensive property
- intensive property
- physical change
- physical property
Check Your Understanding
Recalling Prior Knowledge
- What are some physical properties that can be used to describe matter?
- What are the three states of matter? Describe their similarities and differences.
The science of chemistry is largely concerned with the understanding and classification of matter. This understanding naturally begins with careful observations. What does a particular sample of matter look like? Is it a solid, liquid, or gas? Is it hard or soft? Is it shiny or dull? These types of questions are where we will begin our study of matter and its properties.
If you would like to refresh your memory about states of matter, go to “The Phantom's Portrait Parlor: Phases of Matter” at www.miamisci.org/af/sln/phases/watersolid.html and view solids, liquids, and gases at the molecular level.
Description of Matter
Recall that matter is considered to be anything that has mass and occupies space. Matter can be best understood in terms of its properties. Some properties of matter can be determined without altering the identity of the matter, and it is there that we will begin.
Figure below shows two very different objects. Each has a different chemical composition, meaning that each is made up of a different type of matter.
(A) This lamp from the country of Sri Lanka is made of silver. (B) These large salt mounds from Bolivia were produced during a salt mining operation.
Silver and ordinary table salt are two examples of chemical substances. A substance is matter that has a uniform and definite composition. All samples of substances, sometimes called pure substances, have identical properties.
A physical property is a characteristic of a substance that can be observed or measured without changing the identity of the substance. For example, silver is a shiny metal that conducts electricity very well. It can also be molded into thin sheets, a property called malleability. These are all physical properties of silver. In contrast, salt is dull and brittle, but it can also conduct electricity after being dissolved in water, which it does quite readily. In addition to color, hardness, malleability, solubility, and electrical conductivity, some other physical properties of matter include density, melting point, and boiling point.
There are many examples of physical properties that can be further investigated on the internet.
Extensive and Intensive Properties
Some properties of matter depend on the size of the sample, while some do not. An extensive property is a property that depends on the amount of matter in a sample. The mass of an object is a measure of the amount of matter that an object contains. A small sample of a certain type of matter will have a small mass, while a larger sample will have a greater mass. Another extensive property is volume. The volume of an object is a measure of the space that is occupied by that object.
An intensive property is a property of matter that depends only on the type of matter in a sample and not on the amount. For example, the electrical conductivity of a substance is a property that depends only on the type of substance. Silver, gold, and copper are excellent conductors of electricity, while glass and plastic are poor conductors. A larger or smaller piece of glass will not change this property. Other intensive properties include color, temperature, density, and solubility.
For more information on extensive and intensive properties, visit www.chem.tamu.edu/class/majors/tutorialnotefiles/intext.htm.
States of Matter
Water is a very common substance that we frequently encounter in all three states of matter, as seen in Figure below. 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 a substance does not change when it is melted, frozen, or boiled.
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.
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 (Figure below). Solids are almost completely incompressible, meaning that solids cannot be squeezed into a smaller volume. When a solid is heated, it expands only slightly.
The particles of a gas are very far apart compared to the particles of a liquid or a solid.
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 sample does not change, because the water molecules are still relatively close to one another in the liquid state. Its ability to flow means that water is considered a fluid. Unlike a solid, the arrangement of particles in a liquid is not rigid and orderly. Liquids are also incompressible, and the volume of water expands slightly when heated.
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, very far apart from one another compared to the particles that make up solids and liquids. Gases, like liquids, are fluids. Gases are easily compressed because of the large spaces in between gas particles. The term gas is most often used to refer to a substance that is found in the gas state at room temperature, such as hydrogen and nitrogen. However, substances that are solids or liquids at room temperature can also evaporate into the gaseous state. A vapor is the gaseous state of a substance that is a solid or liquid at room temperature. Examples include water vapor or sodium vapor (Figure below).
Sodium vapor lamps glow with a distinctive yellow color.
For a summary of the phases of matter, visit www.chem.purdue.edu/gchelp/atoms/states.html.
A fun, interactive simulation about phases of matter can be downloaded at www.concord.org/activities/states-matter.
Another interactive simulation that will help you understand solids, liquids, and gases can be found at http://phet.colorado.edu/en/simulation/states-of-matter. A variety of activity guides can be found by scrolling down.
NASA provides diagrams and explanations of states of matter at http://www.grc.nasa.gov/WWW/k-12/airplane/state.html
NASA explains properties of gases in an informative website at http://www.grc.nasa.gov/WWW/k-12/airplane/gasprop.html.
As an ice cube melts, its shape changes as it acquires the ability to flow. However, its composition does not change. Melting is an example of a physical change. A physical change is a change to a sample of matter in which some properties of the material change, but the identity of the matter does not. Physical changes can further be classified as reversible or irreversible. The melted ice cube may be refrozen, so melting is a reversible physical change. Physical changes that involve a change of state are all reversible. Other changes of state include vaporization (liquid to gas), freezing (liquid to solid), and condensation (gas to liquid). Dissolving is also a reversible physical change. When salt is dissolved in water, the salt is said to have entered the aqueous state. Boiling off the water will cause the salt to reform in its solid state.
An example of an irreversible physical change would be grinding a piece of wood into sawdust. Such a change is irreversible because the sawdust cannot be reconstituted into the same piece of wood that it was before. Cutting the grass or pulverizing a rock would be other irreversible physical changes.
Some other examples of physical changes can be seen on the web:
- A substance is a sample of matter with a fixed composition and identifiable physical properties that are the same for every sample of a particular substance.
- Extensive properties depend on the size of a sample, while intensive properties do not.
- Solid, liquid, and gas are the three common states of matter.
- Physical changes do not alter the identity of a substance.
Lesson Review Questions
- Explain why water is considered a substance, while milk is not.
- List at least three physical properties of silver.
- Give an example of an extensive property and of an intensive property of an iron nail. Explain.
- Compare the arrangements of particles in the three states of matter.
- The odor of gasoline is very strong and distinctive. Should gasoline in the gaseous state be called a gas or a vapor? Explain.
- Describe how the sharpening of a pencil is a different type of physical change than dissolving some sugar in water.
Use the Table below to answer the following questions.
Properties of Substances
Melting Point (°C)
Boiling Point (°C)
- What is the physical state of each of the following substances at room temperature?
- What is the name of the physical change that occurs in each of the following instances?
- Oxygen is cooled from −150°C to −200°C.
- Iron is cooled from 1600°C to 1500°C.
- Mercury is heated from −130°C to -100°C.
- Which colorless substance is a solid at −50°C?
- Which substance is a liquid at 1000°C?
- Which substance condenses from a gas to a liquid as the temperature is cooled from 20°C to −50°C?
Further Reading / Supplemental Links
Points to Consider
A mixture is different from a pure substance because it does not have a uniform and definite composition. Pure substances include both elements and compounds.
- Can mixtures be further classified into more than one type?
- How are compounds different than elements?