CHAPTER 2 PROPERTIES OF MATTER - Wikispaces：2章性能Wikispaces物.doc

CHAPTER 2: PROPERTIES OF MATTER2.1 OBJECTIVESn Students will be able to: Classify pure substances as elements or compounds Describe the characteristics of an element Describe the characteristics of a compound Distinguish pure substances from mixtures Classify mixtures as “hetero” or “homo” Classify mixtures as solutions, suspensions, or compounds.I. Why are elements and compounds classified as pure substances? A. A pure substance is matter that always has exactly the same composition. 1. Table salt and table sugar are two examples of pure substances. 2. Substances can be classified into two categorieselements and compounds.B. Every sample of a given substance has the same properties because a substance has a fixed, uniform composition. II. How do mixtures differ from pure substances?A. An element is a substance that cannot be broken down into simpler substances.B. Examples of Elements Some elements are solids at room temperature. The elements oxygen and nitrogen are the main gases in the air you breathe. Two elements are liquids at room temperaturebromine and mercury. III. Symbols for ElementsA. Chemists use symbols of one or two letters to represent elements.IV. How do mixtures differ from pure substances? A. A compound always contains two or more elements joined in a fixed proportion.B. The properties of a compound differ from those of the substances from which it is made. 1. Water is composed of the elements hydrogen and oxygen. Oxygen and hydrogen are gases at room temperature, but water is a liquid.2. Hydrogen can fuel a fire, and oxygen can keep a fire burning, but water does not burn or help other substances to burn.V. How do mixtures differ from pure substances? A. The properties of a mixture can vary because the composition of a mixture is not fixed.VI. Mixtures can be classified by how well the parts of the mixture are distributed throughout the mixture.A. Heterogeneous Mixtures ex. SALSA1. the parts of the mixture are noticeably different from one another.B. Homogeneous Mixtures example: Kool-Aid1. the substances are so evenly distributed that it is difficult to distinguish one substance in the mixture from another.VII. What is the main difference among solutions, suspensions, and colloids?A.Solutions Example: windshield wiper fluidWhen substances dissolve and form a homogeneous mixture, the mixture that forms is called a solution.B. Suspensions Example: muddy waterA suspension is a heterogeneous mixture that separates into layers over time.C. Colloids Example: milkA colloid contains some particles that are intermediate in size between the small particles in a solution and the larger particles in a suspension. OBJECTIVES 2.2n Students will be able to: Describe physical properties of matter. Identify substances based on their physical properties. Describe how properties are used to choose chemicals. Describe methods used to separate mixtures. Describe evidence that a physical change has taken place.I. What are some examples of physical properties?A. physical property is any characteristic of a material that can be observed or measured without changing the composition of the substances in the material.B. ViscosityThe tendency of a liquid to keep from flowing is called its viscosity. 1. Thick liquids, such as corn syrup and honey, have a high viscosity. 2. Thin liquids, such as vinegar and water, have a low viscosity. C. ConductivityA materials ability to allow heat to flow is called conductivity.1. Materials that have a high conductivity, such as metals, are called conductors.D. MalleabilityThe ability of a solid to be hammered without shattering is malleability.1. Most metals, such as gold, are malleable. 2. An ice cube or piece of glass breaks into small pieces when struck with a hammer. Solids that shatter when struck are brittle, not malleable.E. Hardness1. One material can scratch another material if it is harder than the other material. a. A kitchen knife can scratch a copper sheet because stainless steel is harder than copper.b. Diamond is the hardest known material.F. Melting and Boiling Points1. The temperature at which a material changes state is a physical property.The temperature at which a substance changes from solid to liquid (melts) is its melting point.The temperature at which a substance changes from liquid to gas (boils) is its boiling point. G. Density1. The ratio of the mass of a substance to its volume is its density.2. Water has a density of 1.0density1.0 will sink in waterII. How can knowing the physical properties of matter be useful? A. Using Properties to Identify Materials1. Decide which properties to test. 2. Do tests on a sample of the unknown material.3. Compare the results with the data reported for known materials.III. What processes are used to separate mixtures? A. FiltrationYou can separate hot tea from loose tea leaves by pouring the mixture through a strainer. Filtration is a process that separates materials based on the size of their particles.B. Distillation1. process that separates the substances in a solution based on their boiling points.IV. A physical change occurs when some of the properties of a material change, but the substances in the material remain the same. A. During a physical change, the size and shape of a material can change but not the composition. Some examples include1. melting butter in a pan2. crumpling a piece of paper3. slicing a tomatoB. Some but not all physical changes can be reversed. Braiding hair is a reversible change. Cutting hair cannot be reversed. OBJECTIVES 2.3n Students will be able to: Describe chemical properties of matter. Describe clues that indicate a chemical change is taking place. Distinguish between chemical changes and physical changes.The ability to burn is not a physical property. As a candle burns, new substances form.I. When can chemical properties be observed? A. As a candle burns, its compounds combine with oxygen in the air to form water and carbon dioxide. B. chemical property is any ability to produce a change in the composition of matter. Chemical properties can be observed only when the substances in a sample of matter are changing into different substances.C. Flammability Materials that burn can be used as fuel. Flammability is a materials ability to burn in the presence of oxygen.D. Reactivity Example: Rust The property that describes how readily a substance combines chemically with other substances is reactivity. II. What observations might indicate that a chemical change has occurred? A. Change in ColorA change in color is a clue that a chemical change has produced at least one new substance.A shiny silver bracelet that is exposed to air will darken. As a match burns, it shrivels up and turns black. A new copper roof and an old copper roof have different colors. B. Product