Part of understanding matter is being able to describe it. One way chemists describe matter is to assign different kinds of properties to different categories.
The properties that chemists use to describe matter fall into two general categories. Physical properties A charactristic that describes matter, such as size, shape, and color. are characteristics that describe matter. They include characteristics such as size, shape, color, and mass. Chemical properties A characteristic that describes how matter changes its chemical structure or composition. are characteristics that describe how matter changes its chemical structure or composition. An example of a chemical property is flammability—a material’s ability to burn—because burning (also known as combustion) changes the chemical composition of a material.
Any sample of matter that has the same physical and chemical properties throughout the sample is called a substance Any sample of matter that has the same physical and chemical properties throughout the sample. . There are two types of substances. A substance that cannot be broken down into chemically simpler components is an element A substance that cannot be broken down into chemically simpler components. . Aluminum, which is used in soda cans, is an element. A substance that can be broken down into chemically simpler components (because it has more than one element) is a compound A substance that can be broken down into chemically simpler components. (Figure 1.2 "The General Steps of the Scientific Method"). Water is a compound composed of the elements hydrogen and oxygen. Today, there are about 118 elements in the known universe. In contrast, scientists have identified tens of millions of different compounds to date.
Sometimes the word pure is added to substance, but this is not absolutely necessary. By definition, any single substance is pure.
The smallest part of an element that maintains the identity of that element is called an atom The smallest part of an element that maintains the identity of that element. . Atoms are extremely tiny; to make a line 1 inch long, you would need 217 million iron atoms. The smallest part of a compound that maintains the identity of that compound is called a molecule The smallest part of a compound that maintains the identity of that compound. . Molecules are composed of atoms that are attached together and behave as a unit. Scientists usually work with millions and millions of atoms and molecules at a time. When a scientist is working with large numbers of atoms or molecules at a time, the scientist is studying the macroscopic A view of the universe in which one is working with large numbers of atoms or molecules at a time. view of the universe. However, scientists can also describe chemical events on the level of individual atoms or molecules, which is referred to as the microscopic A view of the universe in which one is working with a few atoms or molecules at a time. viewpoint. We will see examples of both macroscopic and microscopic viewpoints throughout this book (Figure 1.3 "How Many Particles Are Needed for a Period in a Sentence?").
Figure 1.3 How Many Particles Are Needed for a Period in a Sentence?
Although we do not notice it from a macroscopic perspective, matter is composed of microscopic particles so tiny that billions of them are needed to make a speck we can see with the naked eye. The ×25 and ×400,000,000 indicate the number of times the image is magnified.
A material composed of two or more substances is a mixture A sample composed of two or more substances. . In a mixture, the individual substances maintain their chemical identities. Many mixtures are obvious combinations of two or more substances, such as a mixture of sand and water. Such mixtures are called heterogeneous mixtures A mixture that is a combination of two or more substances. . In some mixtures, the components are so intimately combined that they act like a single substance (even though they are not). Mixtures with a consistent composition throughout are called homogeneous mixtures (or solutions) A mixture that acts as a single substance so that it is not obvious that two or more substances are present. . Sugar dissolved in water is an example of a solution. A metal alloy, such as steel, is an example of a solid solution. Air, a mixture of mainly nitrogen and oxygen, is a gaseous solution.
How would a chemist categorize each example of matter?
How would a chemist categorize each example of matter?
