1. Compounds, Mixtures, and Reactions Unit II-Part 5

2. Classifying Matter Matter Pure SubstancesMixtures ElementsCompounds HomogeneousHeterogeneous Fe, OH 2 O, CO 2 milk, tea Rocky Road ice cream, muddy water

3. What is a Pure Substance? A pure substance is a classification of matter that includes both elements and compounds Pure substances cannot be separated by physical means such as distillation, filtration, or chromatography

4. Elements We have already studied elements − An element is made of one kind of atom − Found on the periodic table

5. What Is A Compound? A compound is a pure substance that is created by 2 or more elements chemically reacting and joining together − Ex: NaCl, H 2 O, CO 2, NH 3, NaHCO 3, and C 6 H 12 O 6 Notice that elements combine in many ways to make compounds − Ex: H 2 O, H 2 O 2, CO, and CO 2

6. Why Do Compounds Form? Compounds form to allow elements to become more stable − Na is flammable when it comes in contact with H 2 O, and Cl 2 is a toxic gas − NaCl is a very stable compound that is neither flammable nor toxic (in normal quantities) Compounds that are extremely unstable will break down to form the more stable elements

7. How Do Compounds Form? Compounds form by the interaction between the nuclei and valence electrons of 2 or more elements THE OCTET RULE: an element is most stable with 8 valence electrons − Elements will join chemically to get 8 valence electrons Ex: CO 2 : oxygen has 6 valence electrons and carbon has 4 If the carbon shares 2 with each oxygen, everyone will have 8 valence electrons!

8. What Do Compounds Have To Do With My Life? Compounds are the substances that make up ALL living and non-living things Examples: Where would you be without: − H 2 O—water − NaCl—table salt − C 3 H 8 O—rubbing alcohol − C 55 H 98 O 6 —an example of an unsaturated fat

9. What Is A Mixture? A mixture is the physical combination of 2 or more substances It is important to understand that a mixture is not chemically combined Mixtures can be separated by physical means such as filtration, distillation, and chromatography Mixtures can be divided into 2 groups − Homogenous mixtures − Heterogeneous mixtures

10. How Do Mixtures Form ? Mixtures form by physically “junking” 2 or more substances together Remember no chemical change is occurring The formation of a mixture is not a result of lowering energy

11. What Is a Homogenous Mixture? A homogeneous mixture is a mixture that is evenly distributed Homogeneous mixtures are commonly called solutions. − Solution = Solute + Solvent Solute: “stuff” being dissolved Solvent: “stuff” doing the dissolving The solvent is present in greater quantity The solute is present in the lesser quantity − Ex: Salt water: Salt=solute, Water=solvent

12. What Is a Heterogeneous Mixture? A heterogeneous mixture is a mixture that is unevenly distributed. Examples: − Iced tea: The ice is floating at the top and therefore is not evenly distributed throughout the tea − Chex Mix: You may find a different number of pretzels or Chex cereal in each handful; therefore, the mixture is unevenly distributed

13. How Are Mixtures Important To My Life ? We encounter mixtures everywhere in our lives Where would you be without: − Ice cream − Kool-aid − Shampoo − Soup − Milk − Orange juice

14. How Can We Change Matter Into New Substances? Chemical reaction (also known as a chemical change) is a change in a substance or substances that results in a totally new substance − Ex: 2H 2 (g) + O 2 (g)  2H 2 O(g) Notice that the reactants (the substances you start with) combine to form a new substance (the product)

15. How Do I Know If A Chemical Reaction Has Occurred? There are 5 indicators of a chemical reaction 1.Evolution of a gas 2.Evolution of light 3.Evolution of heat 4.Color change 5.Evolution of a precipitate Precipitate: an insoluble substance that is produced as result of a chemical reaction

16. Why Do Chemical Reactions Occur? Chemical reactions occur to produce a more stable product than the existing reactants − Ex: 2Na(s) + Cl 2 (g)  2NaCl(s) *The sodium is highly unstable and the chlorine gas is somewhat unstable. The resulting Sodium Chloride is VERY stable. **It is important to understand that the products have totally different properties than the reactants

17. Where Does The Matter Go? It is important to understand that when matter undergoes a chemical reaction (ie a chemical change) it does not disappear or appear − The atoms are rearranged and form new bonds, but no matter is lost nor gained This is called the Law of Conservation of Matter

18. What Kind of Chemical Reactions Do I Experience? The acidic milk and basic baking soda that produce CO 2 gas when a cake bakes Paper burning to produce ashes, CO 2, and H 2 O vapor Hydrogen peroxide decomposing to produce water and oxygen gas