Ch. 2 Learning Objec1ves 1.  I can classify pure substances. This means that I know the difference between an element and a compound. 2.  I can describe the characteristics of an element. This means that I know how elements are identified by using chemical symbols. 3.  I can describe the characteristics of a compound. The means that I know the difference between a compound and other pure substances. 4.  I can distinguish a pure substance from a mixture. This means that I know what makes them different. Learning Objec1ves Con1nued 5.  I can classify mixtures. This means that I know what a 6. 
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homogeneous and heterogeneous mixture is. I also know what a solution, suspension, and colloid is. I can describe the physical properties of matter. This means that I know what each property is and how we can identify them. I can describe how to separate a mixture. This means I can differentiate between filtration and distillation. I can describe the chemical properties of matter. This means I can list the different properties. I can describe how to tell that a change has a occurred. This means I can state the three ways to tell a change has happened. Section 2.1: Classifying Matter Pure Substances —  Matter that always has exactly the same composition is classified as a pure substance. —  Examples: salt and sugar —  **Every sample of a given pure substance has the same properties because a pure substance has a fixed, uniform composition. —  Pure substances are classified into two categories: elements and compounds. Elements —  An element is a substance that cannot be broken down into simpler substances. —  An atom is the smallest particle of an element. —  **An element has a fixed composition because it contains only 1 type of atom. —  No two elements contain the same type of atom. Examples of Elements —  Solid elements at room temperature —  Aluminum —  Carbon —  Gas elements at room temperature —  Oxygen —  Nitrogen —  Liquid elements at room temperature —  Bromine —  Mercury Symbols for Elements —  Jons Berzelius, a Swedish chemist, suggested that chemists use symbols to represent elements. —  Characteristics of symbols: —  1 or 2 letters (First letter is always capitalized) —  Still used on the periodic table today. —  Why is using symbols important? —  So there is a universal symbol for all languages. Compounds —  Water is composed of the elements hydrogen and oxygen —  Compounds: made from two or more simpler substances that can be broken down into those simpler substances. Mixtures —  **The properties of a mixture can vary because the composition of a mixture is not fixed. Mixtures —  In a heterogeneous mixture, the parts of the mixture can be classified and noticeably different from one another. Mixtures con1nued —  In a homogeneous mixture, substances are so evenly distributed that it is difficult to identify one part from the next! —  Appears to be only one substance. Solu1ons, Suspensions, and Colloids —  **Based on the size of its largest particles a mixture can be classified as a solution, a suspension, or a colloid Solu1ons —  When substances dissolve and form a homogeneous mixture, the mixture that forms is called a solution. — 
Example: sugar and water —  Liquid Solutions-­‐are homogeneous mixtures! —  Do not separate —  Can not be filtered —  Clear **The particles in a solution are TOO SMALL to settle out of the solution, be trapped by a filter, or scatter light Suspensions —  A suspension is a heterogeneous mixture that separates into layers over time. —  Example: sand and water —  Can a suspension be filtered? —  YES!! Colloids —  A colloid contains particles that are medium size! They are in between the small particles in a solution and the larger particles in a suspension. —  Do not separate into layers —  Can not be filtered —  Examples: Fog Physical Proper1es —  A physical property is any characteristic of a material that can be observed or measured without changing the composition of substances in a material. Examples of Physical Proper1es —  Viscosity —  Conductivity —  Malleability —  Hardness —  Melting point —  Boiling point —  Density Viscosity —  The resistance to flow —  The greater the viscosity the slower the liquid moves —  High viscosity liquids: honey, corn syrup —  Low viscosity liquids: vinegar , water —  Viscosity will decrease when the liquid is heated. Conduc1vity —  Ability to allow heat to flow —  Materials with high conductivity are called conductors. —  Example: Metals Other Proper1es —  Malleability – the ability of a solid to be hammered without shattering. —  Hardness – diamond is the hardest know material —  Melting and Boiling Points —  When a material has reached its boiling point the material changes from a liquid to a gas Density —  Density – is used to test purity of a substance Using Physical Proper1es —  How are physical properties used: —  To identify a material —  To choose a material for a specific purpose —  To separate substances in a mixture Using Proper1es to Iden1fy Materials —  What are the three steps used to identify a material? 1.  Decide which properties to test 2.  Test on the unknown sample 3.  Compare results with data for known materials —  Why is identifying a material important? —  To solve crimes Using Proper1es to Separate Mixtures —  What are the two separation methods? —  Filtration and Distillation —  Filtration-­‐ the process that separates materials based on the size of the particles. —  Distillation-­‐ process that separates the substances in a solution based on their boiling points. — 
Example: providing fresh water Recognizing Physical Changes —  When does a physical change occur? —  When some of the properties of a material change, but the substances in the material stay the same. —  Two examples: Observing Chemical Proper1es —  What is a chemical property? —  Any ability to produce a change in the composition of matter. —  When can a chemical property be observed? —  When the substances in matter are changing into different substances. —  What are the two examples of chemical properties? Flammability and Reactivity —  Flammability – material’s ability to burn in the presence of oxygen —  Reactivity – how readily a substance combines chemically with other substances. —  Example: Oxygen is a highly reactive element and nitrogen has an extremely low reactivity. Recognizing Chemical Changes —  When does a chemical change occur? —  When a substance reacts and forms one or more new substances. —  Examples of a chemical change —  Baking a cake —  Ripening bananas —  Leaves on a tree changing color Evidence of a chemical change —  Change in color —  Production of gas —  Formation of precipitate Is A Change Chemical or Physical? —  What should you ask yourself before deciding if a chemical change has occurred? —  Did the matter turn into something completely new? If so, it’s a chemical change! —  **Matter changes= CHEMICAL CHANGE **Matter stays the same= PHYSICAL CHANGE