1. Chapter 3 MATTER AND CHANGE

2. Pure substance or a mixture? A substance is matter, either an element or compound, with the same fixed composition and properties. A sample of matter is either pure—made up of only one kind of matter— or it is a mixture of different kinds of matter.

3. Physical properties are characteristics that a sample of matter exhibits without any change in its identity. Extensive or intensive

4. Examples of the physical properties of a chunk of matter include its: solubility, melting point, boiling point, color, density, electrical conductivity, and physical state (solid, liquid, or gas).

5. Chemical Properties Chemical properties are those that can be observed only when there is a change in the composition of the substance. Rusting is a chemical reaction in which iron combines with oxygen to form a new substance, iron (III) oxide. Inability to react is also a chemical property.

6. States of Matter Most matter on Earth exists in one of three physical states: solid, liquid, or gas. A fourth state of matter, called plasma, is less familiar. Changes in state are examples of physical changes because there is no change in the chemical composition identity of the substance. Ice can melt back to form liquid water, and steam will condense on a cool surface to form liquid water.

7. States of Matter Some substances are described as volatile, which means that they change to a gas easily at room temperature. Alcohol and gasoline are more volatile than water. Density is the amount of matter (mass) contained in a unit of volume. Styrofoam has a low density or small mass per unit of volume.

8. A physical change is a change in matter that does not involve a change in the chemical identity of individual substances. Examples of physical changes include: boiling, freezing, melting, evaporating, dissolving, and crystallizing.

9. Chemical Changes All matter is made of atoms, and any chemical change involves only a rearrangement of the atoms. Atoms do not just appear. Atoms do not just disappear. This is an example of the law of conservation of mass, which says that in a chemical change, matter is neither created nor destroyed. It would be equally correct to call this the law of conservation of matter.

10. A mixture is a combination of two or more substances in which the basic identity of each substance is not changed. Unlike pure substances, mixtures do not have specific compositions. Pure substance or a mixture?

11. A heterogeneous mixture is one with different compositions, depending upon where you look. The components of the mixture exist as distinct regions, often called phases. Pure substance or a mixture?

12. Homogeneous mixtures are the same throughout. Another name for a homogeneous mixture is solution. Pure substance or a mixture? Some solutions are gases. Air, for example, is a homogeneous mixture of several gases. Some solutions are solids.

13. Alloys are solid solutions that contain different metals and sometimes nonmetallic substances. Pure substance or a mixture?

14. When you dissolve sugar in water, sugar is the solute—the substance being dissolved. The substance that dissolves the solute, in this case water, is the solvent. When the solvent is water, the solution is called an aqueous solution. Pure substance or a mixture?

15. Many of the solutions you encounter are aqueous solutions, for example, soda, tea, contact-lens cleaner, and other clear cleaning liquids. In addition, most of the processes of life occur in aqueous solutions. Pure substance or a mixture?

17. Two Types of Substances One type of pure substance can be broken down into simpler substances. This type of substance is called a compound. Another type of substance cannot be broken down into simpler substances. Such a substance is called an element. All the substances of the universe are either elements, compounds formed from elements, or mixtures of elements and compounds.

18. Two Types of Substances Of the known elements, only about 90 occur naturally on Earth. The remainder are synthesized, usually in barely detectable amounts, in high-energy nuclear experiments. Less than half of the 90 naturally occurring elements are abundant enough to play a significant role in the chemistry of everyday stuff.

19. Organizing the Elements The periodic table organizes elements in a way that provides a wealth of chemical information—much more than is evident to you now. It shows the chemical symbols for the elements. Their symbols usually correspond to their names in Latin.

20. Periodic Table of the Elements

21. Compounds Are More Than One Element A more complete definition is that a compound is a chemical combination of two or more different elements joined together in a fixed proportion with a unique set of chemical and physical properties.

22. Compounds Are More Than One Element The properties of the compound are different from the properties of the elements that compose the compound. silver + bromine = silver bromide

23. Compounds Are More Than One Element More than 10 million compounds are known and the number keeps growing. New compounds are discovered and isolated from natural chemical sources such as plants and colonies of bacteria and are synthesized in laboratories for many different uses.

24. Compounds Are More Than One Element A formula is a combination of the chemical symbols that show what elements make up a compound and the number of atoms of each element. CompoundFormula CaffeineC 8 H 10 N 4 O 2

25. Compounds Are More Than One Element Formulas provide a shorthand way of describing a submicroscopic view of a compound. You probably already use formulas like H 2 O and CO 2 as a way of talking about water and carbon dioxide.

26. Percent by mass = mass of element X 100 mass of compound Law of definite proportions – a compound is always composed of the same elements in the same proportion by mass.

27. Law of multiple proportions – when different compounds are formed by a combination of the same elements, different masses of one element combine with the same relative mass of the other element in a ratio of small whole numbers.

28. Question 1 Identify each of the following as either a compound or a mixture. A. sand B. water C. juice

29. Answers A. sand B. water C. juice mixture compound mixture

30. Classify each of the following as a chemical or physical property. Question 2 A. density B. reactivity C. color D. melting point

31. Answers A. density B. reactivity C. color D. melting point physical property chemical property physical property