CHAPTER 17:CLASSIFICATION OF MATTER Section 1—Composition of Matter MATERIALS ARE MADE OF A PURE SUBSTANCE OR A MIXTURE OF SUBSTANCES. A PURE SUBSTANCE, or simply a substance, is either an element ( iron or silver) or a compound (NaCl, H2O). Substances cannot be broken down into simpler compounds and still maintain the properties of the original substances. (Ex.’s –helium, aluminum, water, salt) E E C C ELEMENTS All substances are built from atoms. If all the atoms in a substance are alike, that substance is an element. (Ex.’s--graphite in pencil—all carbon atoms; copper coating in pennies—all copper atoms; gold bar—all gold) COMPOUNDS 2 or more elements can combine to form substances called compounds. A compound is a substance in which the atoms of 2 or more elements are combined. (Ex. Water=H2O—2 atoms of hydrogen, 1 atom of oxygen. MIXTURES—A mixture that can be distinguished easily is called a heterogeneous mixture. Heterogeneous mixtures—are mixtures made of 2 or more substances that can be easily separated by physical means. (Ex. Bowl of mixed nuts) HETEROGENEOUS MIXTURE You might be wearing another heterogeneous mixture…permanent -press fabrics contain fibers of 2 materials (POLYESTER AND COTTON) MOST OF THE SUBSTANCES YOU COME INTO CONTACT WITH EVERY DAY ARE HETEROGENEOUS MIXTURES. Some are easy to see, like the ingredients in a PIZZA, but others are not. In fact, the component you see can be a mixture itself. (Ex. CHEESE--contains milk, proteins, butter fat, colorings, and other food additives.) HOMOGENEOUS MIXTURES A homogeneous mixture contains 2 or more gaseous, liquid, or solid substances blended evenly throughout. Ex. Soft drink: water, sugar, flavoring, coloring, and carbon dioxide gas—can/flat—NOT OPEN Another name for a homogenous mixture is called a solution. A solution’s particles are so small that they cannot be seen with a microscope and will NEVER settle to the bottom of their container. COLLOID A colloid is a type of mixture that never settles. Its particles are larger than those in solutions, but NOT heavy enough to settle. (Ex. Milk, fog, smoke) COLLOIDS FOREST--FOG HEAD LIGHTS--FOG DETECTING COLLOIDS—You can tell for certain if a liquid is a colloid by passing a beam of light through it. A light beam is INVISIBLE as it passes through a solution, BUT can be SEEN as it passes through a colloid. The particles in a colloid are LARGE enough to SCATTER light, but those in a solution are NOT. The SCATTERING OF LIGHT by colloidal particles is called the Tyndall effect. SUSPENSIONS Some mixtures of neither solutions nor colloids. (Ex. MUDDY pond water, apple CIDER (NOT juice) POND WATER is a suspension, which is a heterogeneous mixture containing a liquid in which visible particles SETTLE. Other examples--orange juice with pulp, liquid medicines HOMOGENEOUS OR HETEROGENEOUS MIXTURE? CHAPTER 17:CLASSIFICATION OF MATTER Section 2- Properties of Matter PHYSICAL PROPERTIES Any characteristics of a material that you can observe without changing the identity of the substances that make up the material is a physical property. Examples--APPEARANCE: color, shape, size, melting point, boiling point; BEHAVIOR: attraction to a magnet, ability to flow PHYSICAL PROPERTIES—The best way to separate substances depends on their physical properties. SIZE—ROCKS/SAND MAGNETISM— IRON/SAND PHYSICAL CHANGE A change in SIZE, SHAPE, OR STATE OF MATTER is called a physical change. These changes might involve energy changes, but the kind of substance—the IDENTITY of the element or compound— DOES NOT CHANGE. DISTILLATION Distillation is a process for separating substances in a mixture by EVAPORATING liquid and RECONDENSING its vapor. Ex. Purifying water (distilled water) CHEMICAL PROPERTIES A chemical property is a characteristic of a substance that indicates whether it can change into another substance. Ex. Flammability, or the tendency of a substance to burn, because burning produces NEW SUBSTANCES. DETECTING CHEMICAL CHANGE A change of one substance to another is a chemical change. Ex.’s—RUST on car fenders, SMELL of rotten eggs, food BURNING in the oven, FOAMING of an antacid tablet in water In some chemical changes, a RAPID RELEASE OF ENERGY---detected as HEAT, LIGHT, AND SOUND—are CLUES that changes are occurring. WEATHERING—CHEMICAL OR PHYSICAL CHANGE? PHYSICAL CHANGE— Large rocks can split when water seeps into small cracks , freezes, and expands. However, the smaller pieces of newly exposed rock still have the SAME PROPERTIES as the original rock. CHEMICAL CHANGE Solid calcium carbonate, a compound found in limestone, does not dissolve easily in water. However, when the water is slightly acidic, a new compound is formed. Slightly acidic water (CO2 and H2O) and calcium carbonate calcium hydrogen carbonate (NEW SUBSTANCE) Ex.’s—Caves CONSERVATION OF MASS—Matter is neither created nor destroyed during a chemical change. Burning log + oxygen = ashes + smoke + gases that escaped from log LAW OF CONSERVATION OF MASS The MASS of all substances BEFORE a chemical change EQUALS the MASS of all the substances that remain AFTER the change.