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Chapter 2

Chapter 2. 2.1 Classifying Matter. Classifying Items.

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Chapter 2

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  1. Chapter 2 2.1 Classifying Matter

  2. Classifying Items • People classify objects for different reasons. Classifying food into groups, such as grains, vegetables, and fruits help 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. • Devise a classification system for the following items: orange, lime, plum, apply, pear, rose, violet, daisy, gold, and silver. • Explain what criteria you used to place items into each category of your classification system. • (Teacher Note: Try classifying by syllables)

  3. 2.1 Classifying Matter • Pure substances- Matter that always has exactly the same composition. There is a fixed, uniform composition. • Substances can be classified into two categories: • Elements • A substance that cannot be broken down into simpler substances. There are just over 100 elements. • Atom- The smallest particle of an element. • An element has a fixed composition because it contains only one type of atom. • No two elements contain the same type of atom. • Examples:

  4. Pure Substances Con’t. • Compounds • A substance that is made from two or more simpler substances and can be broken down into those simpler substances. • The properties of a compound differ from those of the substances from which it is made. • A compound always contains two or more elements joined in a fixed proportion.

  5. Mixtures • Mixtures tend to retain some of the properties of their individual substances. • The properties of a mixture can vary because the composition of a mixture is not fixed. • Heterogeneous Mixtures - The parts of the mixture are noticeably different from one another. Examples: salads, salsa

  6. Mixtures • Homogeneous Mixtures - The substances are so evenly distributed that it is difficult to distinguish one substance in the mixture from another. Examples: steel, salt water

  7. Solutions, Suspensions, and Colloids

  8. Solutions, Suspensions, and Colloids • Based on the size of its largest particles, a mixture can be classified as a solution, suspension, or colloid. • Solution- Substances dissolve and form a homogeneous mixture. Examples: tap water, windshield-wiper fluid. • Suspensions- Heterogeneous mixture that separates into layers over time. Examples: sand and water, oil and vinegar.

  9. Solutions, Suspensions, & Colloids • Colloids- Contains some particles that are intermediate in size between the small particles of solutions and the large particles of suspensions. Colloids will not separate and cannot be filtered. However, colloids will scatter light. (Tyndall Effect) Example: fog.

  10. Tyndall Effect

  11. 2.2

  12. Section 2: Physical Properties • Let’s play 20 Questions!

  13. Section 2.2 Physical Properties • Physical property- Any characteristic of a material that can be observed or measured without changing the composition of the substance in the material. Examples: viscosity, conductivity, malleability, hardness, melting point, boiling point, and density.

  14. Physical Properties • Viscosity- The tendency of a liquid to keep from flowing. A resistance to flowing. Example: Honey has a high viscosity. • Conductivity- A material’s ability to allow heat to flow. Example: Metal spoon over a stove. • Materials with a high conductivity are called conductors. They are also a good conductor of electricity as well. Wood is a poor conductor.

  15. Physical Properties • Malleability- The ability of a solid to be hammered into thin sheets without shattering. Example: Most metals can be made into coins or foil. Because gold is both malleable and beautiful, it is often used to make jewelry. These ancient gold medallions were made to form a necklace

  16. Physical Properties • Hardness- One way to compare harness of two materials is to see which of the materials can scratch the other. Stainless steel knife blades can scratch copper. Diamond is the hardest known material. This Tlingit carver is using an adze to carve a canoe from Western red cedar. Red cedar is a relatively soft wood

  17. Physical Properties • Melting Point- Temperature at which a substance changes from a solid to a liquid. Example: Ice melts because the melting point of water is 0ºC (32ºF). • Boiling Point- Temperature at which a substance changes from a liquid to a gas or vapor. The table lists the melting points and boiling points for several substances.

  18. Physical Properties • Density- Ratio of the mass of a substance to its volume. This can be used to test the purity of a substance. Examples: Silver has a density of 10.5 g/cm3.

  19. Section 2: Physical Properties • Density • Describes the relationship between mass and volume • Density is the amount of matter in a given amount of space, or volume GOLF 46 grams PING PONG 2 grams

  20. Section 2: Physical Properties • Solving for Density (d) • Density can help identify substances DENSITY = MASS VOLUME

  21. Section 2: Physical Properties • Sample problem: What is the density of an object whose mass is 25g and whose volume is 10 cm3? • Step 1: Write the formula DENSITY = MASS VOLUME

  22. Section 2: Physical Properties • Sample problem: What is the density of an object whose mass is 25g and whose volume is 10 cm3? • Step 2: Identify the variables 25 g 10 cm3

  23. Section 2: Physical Properties • Sample problem: What is the density of an object whose mass is 25g and whose volume is 10 cm3? • Step 3: Put numbers in the equation DENSITY= 25 g 10 cm3

  24. Section 2: Physical Properties • Sample problem: What is the density of an object whose mass is 25g and whose volume is 10 cm3? • Step 4: Solve and circle answer DENSITY= 25 g 10 cm3 Density= 2.5 g/cm3 NO NAKED NUMBERS!!

  25. Using Physical Properties • Physical properties are used to identify a material, to choose a material for a specific purpose, or to separate the substances in a mixture. • Using properties to identify materials • First, decide which properties to test • Second, do tests on the unknown sample • Third, compare results with a known sample • (This is used in crime scene investigations) • Using properties to choose materials • Properties determine which materials are chosen for which uses. Example: shoelaces wouldn’t be made from wood.

  26. Using Physical Properties • Using properties to separate mixtures • Filtration and distillation are two common separation methods. • Filtration- A process that separates materials based on the size of their particles. Example: brewing coffee • Distillation- A process that separates the substances in a solution based on their boiling points. Example: Separate freshwater from seawater.

  27. 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: cutting paper, melting butter. Braiding hair and cutting hair are examples of physical changes. Braiding is a reversible change. Cutting cannot be reversed

  28. Physical & Chemical Properties

  29. 2.3 Chemical Properties • Chemical property- Any ability to produce a change on the composition of matter.  • Chemical properties can only be observed when the substances in a sample of matter are changing into different substances. Examples: flammability and reactivity.

  30. Chemical Properties • Flammability- A material’s ability to burn in the presence of oxygen. Examples: Anything that can be used as a fuel. Wood, gas, paper. • Reactivity- Describes how readily a substance combines chemically with other substances. Example: Iron with oxygen and water will form rust. If you leave your bike out in the rain.

  31. Recognizing a Chemical Change • Chemical change- Occurs when a substance reacts and form one or more new substances. Examples: baking cakes, food digesting. • Three common types of evidence for a chemical change are a change in color, production of a gas, and formation of a precipitate.

  32. Evidence for a Chemical Change • Color Change • Silver bracelets will darken. • Matches burn and turn black. • Copper roofs turn green.

  33. Evidence for a Chemical Change • Production of a gas • Mixing vinegar with baking soda (carbon dioxide gas) • Cakes have gas bubbles in it

  34. Gummy bear

  35. Evidence for a Chemical Change • Formation of a precipitate • Precipitate- Solids form and separate from a liquid mixture • Curdling of milk- adding lemon juice

  36. Physical & Chemical Properties Song

  37. Is a Change Chemical or Physical? • Sometimes gas bubbles or color change is not a chemical change. You must ask yourself: Are different substances present after the change takes place. • When matter undergoes a chemical change, the composition of the matter changes. When matter undergoes a physical change, the composition of the matter remains the same. A blacksmith uses a hammer to shape a horseshoe that has been heated. Although the color of the iron horseshoe changes, no chemical change is occurring

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