Go to section Classifying Items People classify objects for different reasons. Classifying foods into groups, such as grains, vegetables, and fruits helps people plan meals that maintain a healthy diet. Biologists classify organisms into groups that have similar characteristics, which makes the relationships among organisms easier to see. 1.Devise a classification system for the following items: orange, lime, plum, apple, pear, rose, violet, daisy, gold, and silver. 2.Explain what criteria you used to place items into each category of your classification system. Interest Grabber Section 2.1

Go to section Chapter 2 Properties of Matter

Go to section Section 2.1 Classifying Matter

Go to section Pure Substances Matter that always has exactly the same composition Every sample of the substance has the same properties because of a fixed, uniform composition Two categories –Elements Substance that cannot be broken down into simpler substances, only one type of atom Ex- gold, silver, oxygen Each element has its own symbol –Usually first letter or two of name –Universal system- everyone can understand

Go to section –Compounds Substance made of two or more simpler substances chemically combined Properties different from elements that make it up Always contains two or more elements in a fixed proportion Ex. Water (H 2 O), table salt (NaCl), NaOH

Go to section Mixtures Two or more elements or pure substances that are not chemically combined Properties can vary because the composition is not fixed Heterogeneous mixtures –Not evenly distributed –Easy to separate parts (ex. Salad) Homogeneous mixtures –Evenly distributed –Appears as single substance (ex. Steel)

Go to section Solutions, Suspensions, Colloids Solution- one substance dissolves in another and forms a homogeneous mixture that is evenly distributed –Looks like single substance –Ex. Sugar water, salt water Suspension- heterogeneous mixture that separates into layers over time –Ex. Sand and water, muddy water Colloid- contains intermediate particles that can be seen but does not separate –Ex. Jello, fog, mayo

Go to section Distinguishing Features Physical characteristics can be used to describe and distinguish a person from other people. An accurate physical description can often be used to identify a person in a crowd. Practice identifying physical characteristics with the animals listed below. lion cheetah ocelotleopard tigerbobcat 1.What characteristics make these animals similar? 2.What characteristics make them different? Interest Grabber Section 2.2

Go to section Section 2.2 Physical Properties

Go to section Examples of Physical Properties Viscosity- tendency of a liquid to keep from flowing (resistance to flow) –Decreases as a substance is heated –Ex. Motor oil, corn syrup, honey Conductivity- material’s ability to allow heat to flow (or electricity) –Metals usually good Malleability- ability to be hammered into thin sheets –Metals usually malleable b/c electrons slide around each other and make it easier to form shape –Objects that shatter when struck are brittle

Go to section Hardness- ability of one material to scratch another –Diamond- hardest material known Melting and Boiling Points- temperature at which substances go from a solid to a liquid (melting) or a liquid to a gas (boiling) Density- ratio of the mass of a sample of a substance to its volume –Can be used to identify substances –Can be used to test the purity of substances (ex. motorcycle fuel)

Go to section Melting and Boiling Points of Some Substances Figure 12

Go to section Using Physical Properties Using properties to identify minerals –Test sample for physical properties and compare to sample –Ex. Density, specific heat, melting point, etc Using properties to choose materials –Sets of properties are considered before choosing Using properties to separate mixtures –Filtration- process that separates materials based on the size of their particles Ex. Panning for minerals, coffee filter –Distillation- process that separates the substances in a solution based on their boiling points Ex. Convert seawater to fresh, oil separation

Go to section Recognizing Physical Changes Physical Change- occurs when some of the properties of a material change, but the substances in the material remain the same –Examples- melting butter, wrinkling shirt, cutting hair –Some are reversible- phase changes, wrinkling shirt –Some are irreversible- cutting hair, slicing tomato

Go to section Section 2.3 Chemical Properties

Go to section Observing Chemical Properties Chemical Property- any ability to produce a change in the composition of matter –Measure of the potential to undergo chemical change –Can only be observed when happening –Flammability- material’s ability to burn in presence of oxygen (can be good or bad) –Reactivity- how readily a substance combines chemically with other substances (oxygen, water, acids, etc)

Go to section Recognizing Chemical Changes Chemical change- occurs when a substance reacts and forms one or more new substances –Change in color- not most reliable Ex. Tarnish of metals –Formation of a gas Ex. Vinegar and baking soda –Formation of a precipitate Solid that forms and separates from a liquid mixture Ex. cheesemaking –BE SURE THAT NEW SUBSTANCES ARE PRODUCED!!!

Go to section Physical or Chemical ? Unzipping a zipper Digesting an apple Lighting a candle Putting a plug into a socket Framing a poster Smashing a watermelon Fading of dye Healing of wound Dissolving salt in water