Chapter 15: Classification of Matter

Section 1: Composition of Matter

Pure Substances * Each material has its own properties. The properties of materials can be used to classify them into general categories. * Materials are made of a pure substance or a mixture of substances. * Substance: a type of matter with a fixed composition. * A substance can be either an element or a compound. * All substances are built from atoms. * Element: If all the atoms in a substance have the same identity * About 90 elements are found on Earth. * Compound: a substance in which the atoms of two or more elements are combined in a fixed proportion. * Compounds usually look different from the elements in them.
Mixtures * Unlike compounds, mixtures do not always contain the same proportions of the substances that make them up. * Heterogeneous Mixture: A mixture in which different materials can be distinguished easily * Most of the substances you come in contact with every day are heterogeneous mixtures * Heterogeneous mixtures can be hard to detect. * Homogeneous Mixture: contains two or more gaseous, liquid, or solid substances blended evenly throughout. * Another name for homogeneous mixtures like vinegar and a cold soft drink is solution. * Solution: a homogeneous mixture of particles so small that they cannot be seen with a microscope and will never settle to the bottom of their container. * Milk is an example of a specific kind of mixture called a colloid. * Colloid: a type of mixture with particles that are larger than those in solutions but not heavy enough to settle out. * Fog is a colloid composed of water droplets suspended in air. * One way to distinguish a colloid from a solution is by its appearance. * You can tell for certain if a liquid is a colloid by passing a beam of light through it * Tyndall Effect: The scattering of light by colloidal particles * Some mixtures are neither solutions nor colloids. * Suspension: a heterogeneous mixture containing a liquid in which visible particles settle.

Section 2: Properties of Matter

Physical Property: Any characteristic of a material that you can observe without changing the identity of the substances that make up the material. * You can measure some physical properties. * Some physical properties describe the behavior of a material or a substance. * Every substance has a specific combination of physical properties that make it useful for certain tasks. * Physical property can be used to separate substances in a mixture.
Physical Change: A change in size, shape, or state of matter * These changes might involve energy changes, but the kind of substance—the identity of the element or compound—does not change. * Because all substances have distinct properties like densities, specific heats, and boiling and melting points, which are constant, these properties can be used to help identify them when a particular mixture contains substances which are not yet identified. * Color changes can accompany a physical change, too. * Distillation: The process for separating substances in a mixture by evaporating a liquid and recondensing its vapor * Two liquids having different boiling points can be separated in a similar way.
Chemical Properties and Changes * Chemical Property: a characteristic of a substance that indicates whether it can undergo a certain chemical change. * The tendency of a substance to burn, or its flammability, is an example of a chemical property because burning produces new substances during a chemical change. * Reaction to light is a chemical property.
Detecting Chemical Change * Chemical Change: A change of one substance to another. * Clues such as heat, cooling, or the formation of bubbles or solids in a liquid are helpful indicators that a reaction is taking place. * In some chemical changes, a rapid release of energy—detected as heat, light, and sound—is a clue that changes are occurring. * The only sure proof is that a new substance is produced. * Tarnish is a chemical reaction between silver metal and sulfur compounds in the air which results in silver sulfide.
Weathering - Chemical or Physical Change? * The forces of nature continuously shape Earth’s surface. * Weathering can involve physical or chemical change.
Law of Conservation of Mass: the mass of all substances that are present before a chemical change equals the mass of all the substances that remain after the change. * Smoke, heat, and light are given off and the changes in the appearance of a log confirm that a chemical change took place. * Not only is no mass lost during burning, mass is not gained or lost during any chemical change. \n \n