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Ch. 2 Learning Objectives 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.

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Learning Objectives Continued 5. I can classify mixtures. This means that I know what a homogeneous and heterogeneous mixture is. I also know what a solution, suspension, and colloid is. 6. I can describe the physical properties of matter. This means that I know what each property is and how we can identify them. 7. I can describe how to separate a mixture. This means I can differentiate between filtration and distillation. 8. I can describe the chemical properties of matter. This means I can list the different properties. 9. 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.

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Section 2.1: Classifying Matter

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Pure Substances Matter that always has exactly the same composition is classified as a pure substance. Examples: salt and sugar

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**Every sample of a given substance has the same properties because a substance has a fixed, uniform composition. Substances are classified into two categories: elements and compounds.

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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.

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Examples of Elements Solid elements at room temperature Aluminum carbon Gas elements at room temperature Oxygen Nitrogen Liquid elements at room temperature Bromine Mercury

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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.

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Compounds Water is composed of the elements hydrogen and oxygen Compounds Are made from two or more simpler substances that can be broken down into those simpler substances. Always contain 2 or more elements joined in a fixed proportion.

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Mixtures **Properties can vary because the composition of a mixture is not fixed. (this means the composition can change)

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Mixtures In a heterogeneous mixture, the parts of the mixture can be classified and noticeably different from one another.

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Mixtures continued In a homogeneous mixture, substances are so evenly distributed that it is difficult to distinguish one substance from another in the mixture. Appears to be only one substance.

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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

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Solutions When substances dissolve and form a homogeneous mixture, the mixture that forms is called a solution. Example: sugar and water Liquid Solutions 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

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Suspensions Is a heterogeneous mixture that separates into layers over time. Example: sand and water Can a suspension be filtered?

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Colloids A colloid contains some particles that are intermediate in between small particles in a solution and the larger particles in a suspension. Do not separate into layers Can not be filtered Examples: Fog

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Physical Properties A physical property is any characteristic of a material that can be observed or measured without changing the composition of substances in a material.

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Examples of Physical Properties Viscosity Conductivity Malleability Hardness Melting point Boiling point Density

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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.

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Conductivity Ability to allow heat to flow Materials with high conductivity are called conductors. Example: Metals

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Other Properties Malleability the ability of a solid to be hammered without shattering. Hardness diamond is the hardest know material Density is used to test purity of a substance Melting and Boiling Points When a material has reached its melting point the material changes from a solid to a liquid

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Using Physical Properties How are physical properties used: To identify a material To choose a material for a specific purpose To separate substances into a mixture

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Using Properties to Identify Materials What are the three steps used to identify a material? Decide which properties to test Test on the unknown sample Compare results with data for known materials Why is identifying a material important? To solve crimes

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Using Properties to Separate Mixtures What are the two separation methods? 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

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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: ice melting and hair styles

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Observing Chemical Properties What is a chemical property? Any ability to produce a change in the composition of matter. When can a chemical property be observed? Only when the substances in a sample of matter are changing into different substances.

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What are the two examples of chemical properties? Flammability materials ability to burn in the presence of oxygen Reactivity how readily a substance combines chemically with other substances. Oxygen is a highly reactive element and nitrogen has an extremely low reactivity.

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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

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Evidence of a chemical change Change in color Production of gas Formation of precipitate

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Ask yourself Are different substances present after the change takes place?

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Key Point When matter undergoes a chemical change, the composition of the matter changes. When matter undergoes a physical change, the composition of the matter stays the same.

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Homework Page 58 Section 2.3 Assessment Questions # 4-8