Matter: Properties & Changes

1. Chapter 3 Matter—Properties and Changes

2. Classifying Matter • The word composition comes from a Latin word meaning “a putting together,” or the combining of parts into a whole. • Based on their compositions, materials can be divided into pure substances and mixtures.

3. Pure Substances • Matter that always has exactly the same composition is classified as a pure substance, or simply a substance. • Table salt and table sugar are two examples of pure substances. • Every pinch of salt tastes equally salty. Every spoonful of sugar tastes equally sweet.   • Every sample of a given substance has the same properties because a substance has a fixed, uniform composition. • Substances can be classified into two categories—elements and compounds.

4. Examples of Physical Properties • A physical property is any characteristic of a material that can be observed or measured without changing the composition of the substances in the material. • Density, color, odor, taste, hardness, melting point, and boiling point are examples of physical properties.

5. Extensive and Intensive Properties • Extensive properties are properties that are dependent upon the amount of substance present. For example, mass, length, volume. • Intensive properties are properties that are not dependent (independent) of the amount of substance present. For example, density.

6. Using Properties to Identify Materials • The steps used to identify a material are similar to the steps used to test for purity. • The first step is to decide which properties to test. • The second step is to do tests on a sample of the unknown. • The final step is to compare the results with the data reported for known materials.

7. Chemical Properties • A chemical property is any ability to produce a change in the composition of matter. • Chemical properties can be observed only when the substances in a sample of matter are changing into different substances. • Flammability and reactivity are two examples of chemical properties.

8. States of Matter • Materials can be classified as solids, liquids or gases based on whether their shapes and volumes are definite or variable. • Shape and volume are clues to how the particles in the material are arranged.

9. Solids • Solids are the state of matter in which the material has a definite shape and definite volume. • Definite means that the volume and shape of the object does not change as you move it. • But that does not mean that the shape and volume will never change. • In solids, the particles are packed close together in a regular pattern and very orderly arranged on the atomic level.

10. Liquids • Liquid is the state of matter that has a definite volume but no definite shape. • Liquids take the shape of their container and can be poured from one container to another. • The atoms in liquids are still closely packed but are less orderly arranged.

11. Gases • Gases are the state of matter that has no definite shape and no definite volume. • A gas takes the shape and volume of its container. • Gas particles do not have an order arrangement in containers. • They are at random locations throughout the container. • Because of the space among particles in a gas, gases can be compressed into metal containers.

12. Vapors • The words gas and vapor do not mean the same thing. • Gas refers to a substance that is naturally in the gaseous state at room temperature. For example, methane. • Vapor refers to the gaseous state of a substance that is a solid or liquid at room temperature. For example, steam.

13. Recognizing Physical Changes • A physical change occurs when some of the properties of a material change, but the substances in the material remain the same. • For example, if you slowly heat butter in a pan, it changes from a solid to a liquid, but the substances in the butter do not change. • Heating, crumpling a piece of paper and slicing a tomato are all physical changes because they change the size and shape of a material, but not its composition.

14. Chemical Changes • When one or more substance changes into new substances it is called a chemical change, which is commonly referred to as a chemical reaction. • The new substances in the reactions have different compositions and different properties from the substances present before the reaction occurs.

15. Recognizing Chemical Changes • The color change in a banana peel is caused by chemical changes that are taking place in the cells of the banana. • A chemical change occurs when a substance reacts and forms one or more new substances. • Chemical changes occur when a cake bakes in an oven, leaves on trees change color, and food is digested in your stomach.

16. Chemical Changes • How can you recognize a chemical change? You have to look for clues. For example, when food spoils, it often gives off an unpleasant odor. • Three common types of evidence for a chemical change are a change in color, the production of a gas, and the formation of a precipitate.

17. Conservation of Mass • This law says that the mass before and after a chemical reaction remains the same. • It says that mass is neither created or destroyed in a chemical reaction. Massreactants=Massproducts

18. 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. • There are two types of mixtures: Heterogeneous and Homogeneous.

19. Heterogeneous Mixtures • Heterogeneous comes from the Greek words hetero and genus, meaning “different” and “kind.” In a heterogeneous mixture, the parts of the mixture are noticeably different from one another. • Sand is an example of a heterogeneous mixture.

20. Homogeneous Mixtures • In a homogeneous mixture, the substances are so evenly distributed that it is difficult to distinguish one substance in the mixture from another. • A homogeneous mixture appears to contain only one substance. • A serving spoon made of stainless steel represents a homogeneous mixture of iron, chromium, and nickel. • The water in a swimming pool is also an example of a homogeneous mixture.

21. Solutions, Suspensions, and Colloids • It isn't always easy to tell a homogeneous mixture from a heterogeneous mixture. • You may need to observe the properties of a mixture before you decide. • The size of the particles in a mixture has an effect on the properties of the mixture.   • Based on the size of its largest particles, a mixture can be classified as a solution, a suspension, or a colloid.

22. Using Properties to Separate Mixtures • Some properties can be used to separate mixtures. • Filtration, distillation, crystallization and chromatography are common separation methods.

23. Pure Substances • Matter that always has exactly the same composition is classified as a pure substance, or simply a substance. • Table salt and table sugar are two examples of pure substances. • Every pinch of salt tastes equally salty. Every spoonful of sugar tastes equally sweet.   • Every sample of a given substance has the same properties because a substance has a fixed, uniform composition. • Substances can be classified into two categories—elements and compounds.

24. Elements • Although there are millions of known substances, there are only about 100 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 one type of atom. • No two elements contain the same type of atom.

25. Examples of Elements •  At room temperature (20°C, or 68°F), most elements are solids, including the elements aluminum and carbon. • Some elements are gases at room temperature. The elements oxygen and nitrogen are the main gases in the air you breathe. • Only two elements are liquids at room temperature, bromine and mercury, both of which are extremely poisonous.

26. Symbols for Elements • Each element has a symbol that consists of either one or two letters. The first letter is always capitalized. If there is a second letter, it is not capitalized. • For most symbols it is easy to see what they will be, but some come from different languages, like Gold (Au) and silver (Ag).

27. Periodic Table • As new elements were being discovered they were organized in a periodic table. • All elements in the world can be found on the periodic table.

28. Compounds • A compound is a substance that is made from two or more simpler substances and can be broken down into those simpler substances. • The simpler substances are either elements or other compounds. • 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.

29. Law of Definite Proportions • The law of definite proportions says that regardless of the amount, a compound is always composed of the same elements in the same proportion by mass. • For example, sucrose. In 20.00 g, there are always 8.44 g of carbon, 1.30 g of hydrogen and 10.26 g of oxygen. • The proportion is obtained by calculating the percent by mass.

30. Percent by Mass • Percent by mass of found of the elements in a compound by the following formula: Percent by mass = mass of element x 100% mass of compound

31. Law of Multiple Proportions • This law states that when different compounds are formed by a combination of the same elements, different mass one element combine with the same relative mass of the other elements in a ratio of small whole numbers. • See page 76 in your textbook.