1. Compounds, Mixtures, and Elements

2. Take 5 minutes to define Chemistry:

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

4. Chemistry The study of the composition, structure, properties, and reactions of matter, especially of atomic and molecular systems.

5. Matter has many definitions, but the most common is that it is any substance which has mass and Volume (occupies space). What is not Matter? Energy

6. 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

7. Elements − An element is made of one kind of atom − Found on the periodic table − Can not be broken down

8. 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

9. 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

10. 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

11. What Is A Mixture? Not a pure substance! 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

12. 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

13. 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

14. 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

15. 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

17. 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)

18. 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

19. 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

20. 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

21. 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

22. All matter, regardless of state, undergoes physical and chemical changes. These changes can be microscopic or macroscopic.

23. What is a physical change? A physical change occurs when the substance changes state but does not change its chemical composition. For example: water freezing into ice, cutting a piece of wood into smaller pieces, etc. The form or appearance has changed, but the properties of that substance are the same (i.e. it has the same melting point, boiling point, chemical composition, etc.)

24. Melting point Boiling point Vapor pressure Color State of matter Density Electrical conductivity Solubility Adsorption to a surface Hardness

25. A chemical change occurs when a substance changes into something new. This occurs due to heating, chemical reaction, etc. You can tell a chemical change has occurred if the density, melting point or freezing point of the original substance changes. Many common signs of a chemical change can be seen (bubbles forming, mass changed, etc).

26. Reaction with acids Reaction with bases (alkalis) Reaction with oxygen (combustion) Ability to act as oxidizing agent Ability to act as reducing agent Reaction with other elements Decomposition into simpler substances Corrosion

27. Physical properties are those that we can determine without changing the identity of the substance we are studying.

28. The physical properties of sodium metal can be observed or measured. It is a soft, lustrous, silver-colored metal with a relatively low melting point and low density. Hardness, color, melting point and density are all physical properties.

29. Chemical properties describe the way a substance can change or react to form other substances. These properties, then, must be determined using a process that changes the identity of the substance of interest.

30. One of the chemical properties of alkali metals such as sodium and potassium is that they react with water. To determine this, we would have to combine an alkali metal with water and observe what happens. In other words, we have to define chemical properties of a substance by the chemical changes it undergoes.