Each piece of your clothing has a label that recommends cleaning methods. A 100%-cotton shirt may need to be ironed after washing. A cotton and polyester blend fabric may come out of the dryer wrinkle free. There is no cleaning process that works for all materials.

Pure Substances A pure substance is matter that always has exactly the same ___________________________. Table salt and table sugar are two examples of pure substances. Substances can be classified into two categories—elements and compounds. Every sample of a given substance has the same properties because a substance has a fixed, ______________composition.

Elements An element is a substance that_________be broken down into simpler substances. An element has a fixed composition because it contains only one type of ___________. No two elements contain the same type of atom. Examples of Elements Solids at room temperature: Most soft drink cans are made from aluminum. Carbon is the main element in the marks you make with a pencil. Oxygen and nitrogen are the main gases in you breathe. Two elements are liquids at room temperature–bromine and mercury.

Symbols for Elements Chemists use symbols of one or two_________to represent elements. The first letter is always_____________. If there is a second letter, it is not capitalized. Symbols allow scientists who speak different languages to communicate without _________________. C represents carbon. Al represents aluminum. Au represents gold. (The Latin name is aurum.) Gold Aluminum Carbon Iodine

Compounds A compound is a substance that is made from two or more simpler substances and __________broken down into those simpler substances. A compound always contains two or more elements joined in a fixed proportion. The properties of a compound____from those of the substances from which it is made. Water: Oxygen and hydrogen are gases at room temperature, but water is a liquid.

Compounds Silicon dioxide is a compound found in most light-colored grains of sand and in crystals of quartz. It is a colorless, transparent solid. Yet, silicon dioxide is made from a colorless gas (oxygen) and a gray solid (silicon). In silicon dioxide, there are always two oxygen atoms for each silicon atom. Oxygen Silicon Silicon dioxide

Mixtures If you make salsa, a recipe can guide you. You can use exactly the amounts in the recipe, or you can adjust the ingredients to your own taste. Salsa is a mixture. Each batch may be slightly different.

Mixtures The properties of a mixture can vary because the composition of a mixture is not __________. Mixtures can_______some of the properties of their individual substances. The properties of a mixture are less constant than the properties of a substance.

Mixtures Mixtures can be classified by how well the parts of the mixture are distributed throughout the mixture. Heterogeneous Mixtures In a heterogeneous mixture, the parts of the mixture are noticeably__________________from one another. Homogeneous Mixtures In a homogeneous mixture, the substances are so evenly distributed that it is difficult to___________one substance in the mixture from another.

Mixtures The sand is a heterogeneous mixture of different kinds of grains. The spoon is stainless steel, a homogeneous mixture of iron, chromium, and nickel. The_________of the particles in a mixture has an effect on the properties of the mixture.

Solutions, Suspensions, and Colloids Based on the size of its largest particles, a mixture can be classified as a solution, a suspension, or a colloid. Solutions When substances________and form a homogeneous mixture, the mixture that forms is called a solution. Suspensions A suspension is a heterogeneous mixture that separates into___________over time.

Solutions, Suspensions, and Colloids A colloid contains some particles that are ____________in size between the small particles in a solution and the larger particles in a suspension. Like solutions, colloids do not separate into layers. You cannot use a_____to separate the parts of a colloid.

Solutions, Suspensions, and Colloids These liquids represent three categories of mixtures. Windshield wiper fluid is a solution. Muddy water collected from a swamp is a suspension. Milk is a colloid.