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
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Classifying ItemsPeople 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
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Chapter 2
Properties of Matter
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Section 2.1
Classifying
Matter
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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
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– 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 (H2O), table salt (NaCl), NaOH
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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)
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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
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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 cheetahocelot leopardtiger bobcat
1. What characteristics make these animals similar?
2. What characteristics make them different?
Interest Grabber Section 2.2
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Section 2.2
Physical Properties
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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
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• 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)
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Melting and Boiling Points of Some Substances
Figure 12
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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
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Recognizing Physical Changes
• Physical Change- occurs when some of the properties of a material change, but the substances in the material remain the same
