1.1: Matter
Matter is any substance that has volume and mass. In this section, we explore different properties of matter and the need for standard ways to describe them.
First, let's differentiate between extensive and intensive properties. Extensive properties, such as volume and mass, rely on the amount of the substance. Intensive properties, such as density and viscosity, are independent of the amount of matter and inherent to the matter.
Read this text, which gives examples of each type of property.
Scientists classify properties of matter as physical or chemical. Physical properties are those we can observe without altering the identity of the substance. For example, the melting or boiling point of a substance is a physical property because they do not alter the identity of the substance.
We can only observe chemical properties when we alter the identity of the substance. Rusting is an example of a chemical property because it is a chemical reaction that changes the composition of the substance.
Read this text. Pay attention to the chart at the end of the section, which gives examples of some physical and chemical properties of the element sodium (Na).
The three phases of matter are solid, liquid, and gas. Note the differences between these three phases of matter on the microscopic and macroscopic levels.
- Solids, like wooden blocks, have definite shape and definite volume. The particles are ordered and close together.
- Liquids have definite volume and indefinite shape, meaning they take on the shape of the container. A liquid's particles are less ordered, but still relatively close together.
- Gases, such as the air inside balloons, take the shape and volume of their container. Their particles are highly disordered.
Read this text. Pay attention to the first image which shows the microscopic differences between the phases of matter.
Density is an intrinsic property of matter. We define density (d) as the mass or volume of a substance at a given temperature. We write d = m/v where d is density, m is mass, and v is volume. If we know two of the variables in this equation, we can solve for the third algebraically. The units for density are a mass unit divided by a volume unit. The units used to describe density often differ for the phases of matter: solids (g/cm3), liquids (g/mL), and gases (g/L).
After you read this section, try the practice problem examples 1 and 2.
Watch this video for additional practice with density problems as the instructor works through problems using the d = m/v formula.
Chemists classify matter as a pure substance or a mixture. A pure substance consists of only one type of matter, while a mixture consists of multiple types of matter. Pure substances are further categorized as single-element or compound. Mixtures are further categorized as homogeneous (single-phase) or heterogeneous (multiple phases). The distinction between homogeneous and heterogeneous mixtures presented here is dependent on phase, or physical, boundaries. Mixtures, whether homogeneous or heterogeneous, can be separated by physical means into pure substances.
Read this text. Pay attention to the flowcharts that classify types of matter.
In chemistry, we often study changes in matter. Two types of changes can occur in matter: physical and chemical.
To determine whether you are dealing with a physical or chemical change, ask yourself if you can reverse the process to recover the original material. Physical changes can be reversed, but chemical changes generally cannot. For example, ice melting is a physical change because you can re-freeze the water. However, cooking a steak is a chemical change because you cannot recover the raw meat. Note that we discuss the energetics of chemical change more thoroughly in Unit 6.
Watch this video to see examples of physical and chemical changes, and how we can observe a change to classify it.