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Chapter 2

Chapter 2. 2.1 Classifying Matter. 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

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Chapter 2

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  1. Chapter 2 2.1 Classifying Matter

  2. 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:

  3. 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.

  4. 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

  5. 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

  6. Solutions, Suspensions, and Colloids

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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

  12. 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

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. Do Now • Show what you KNOW!!!! Identify the following as a physical property or a chemical property: • Rust • Density • Explosive • Transparency

  20. Physical vs. Chemical Property • PHYSICAL PROPERTY • 1. observed with senses • 2. determined without destroying matter reacts with something else • CHEMICAL PROPERTY • 1. indicates how a substance • 2. matter will be changed into a new substance after the reaction

  21. 2.3 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

  22. 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.

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

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

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

  26. Activity: • In your groups, you will have 10 minutes to organize the following flash cards on the Physical/Chemical Property and Physical/Chemical Change Graph Organizer and make a record of your chart in your notebook. • You may use your notes!!! • Be prepared to Defend your choices!!! • Person 1 – Time keeper • Person 2 – Recorder • Person 3 – Speaker • Person 4 – Researcher • Person 5 – Second Look

  27. Physical vs. Chemical Change • PHYSICAL CHANGE • 1. a change in size, shape, or state • 2. no new substance is formed • CHEMICAL CHANGE • 1. a change in the physical and chemical properties • 2. a new substance is formed

  28. 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. There are four good signs for a chemical reaction (although these do not guarantee a reaction has occurred): • energy change • color change • gas released (sometimes with an odor) • precipitate formed (a precipitate is a solid formed during the reaction of two aqueous solutions) • 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

  29. Exit Ticket • Before you leave….put it all together….identify the following as a physical property, chemical property, physical change, or chemical change. • A. Cut a marshmallow in half • B. Grass growing on the lawn • C. Reddish Brown • D. 45 g of Al • E.C. Identify the following elements: • Atomic number: 13, 10, 3

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