Exploring the Nature of Matter: Chemistry Insights

1. Matter Notes Note :Slide 1-38 (Packet 1 ) , Slide 39-49 (Packet 2) Chemistry Ch 3

2. The Nature of Matter Chemists are interested in the nature of matter and how this is related to its atoms and molecules. Gold Mercury

3. Chemistry & Matter • We can explore the MACROSCOPIC world — what we can see — • to understand the PARTICULATE worlds we cannot see. • We write SYMBOLS to describe these worlds.

4. A Chemist’s View of Water Macroscopic H2O (gas, liquid, solid) Symbolic Particulate

5. A Chemist’s View Macroscopic 2 H2(g) + O2 (g) --> 2 H2O(g) Particulate Symbolic

6. Kinetic Nature of Matter Matter consists of atoms and molecules in motion.

7. STATES OF MATTER • SOLIDS— have rigid shape, fixed volume. External shape can reflect the atomic and molecular arrangement. • Reasonably well understood. • LIQUIDS— have no fixed shape and may not fill a container completely. • Not well understood. • GASES— expand to fill their container. • Good theoretical understanding.

8. OTHER STATES OF MATTER • PLASMA— an electrically charged gas; Example: the sun or any other star

9. Physical Properties of Matter

10. STATES OF MATTER: SOLIDS • Particles of solids are tightly packed, vibrating about a fixed position. • Solids have a definite shape and a definite volume. Heat

11. STATES OF MATTERLIQUID • Particles of liquids are tightly packed, but are far enough apart to slide over one another. • Liquids have an indefinite shape and a definite volume. Heat

12. STATES OF MATTERGAS • Particles of gases are very far apart and move freely. • Gases have an indefinite shape and an indefinite volume. Heat

13. The phase change from a solid to liquid is called melting.

15. 17. Describe how taking a shower is an example of condensation.

16. 18. The phase change from a liquid back to a solid is called Freezing

17. 19. Dry ice turning directly into a gas is an example of what kind of phase change? (solid gas) sublimation

18. Gas – Solid

19. Phase Change

22. Physical Properties What are some physical properties? • color • melting and boiling point • odor

23. Physical properties of matter are categorized as either Intensive or Extensive: • Intensive - Properties that do not depend on the amount of the matter present. • Color • Odor • Luster - How shiny a substance is. • Malleability - The ability of a substance to be beaten into thin sheets. • Ductility - The ability of a substance to be drawn into thin wires. • Conductivity - The ability of a substance to allow the flow of energy or electricity. • Hardness - How easily a substance can be scratched. • Melting/Freezing Point - The temperature at which the solid and liquid phases of a substance are in equilibrium at atmospheric pressure. • Boiling Point - The temperature at which the vapor pressure of a liquid is equal to the pressure on the liquid (generally atmospheric pressure). • Density - The mass of a substance divided by its volume

24. Physical properties of matter are categorized as either Intensive or Extensive: • Extensive - Properties that do depend on the amount of matter present. • Mass - A measurement of the amount of matter in a object (grams). • Weight - A measurement of the gravitational force of attraction of the earth acting on an object. • Volume - A measurement of the amount of space a substance occupies. • Length

25. Physical Changes • can be observed without changing the identity of the substance Some physical changes would be • boiling of a liquid • melting of a solid • dissolving a solid in a liquid to give a homogeneous mixture — a SOLUTION.

26. Chemical Properties and Chemical Change • Burning hydrogen (H2) in oxygen (O2) gives H2O. • Chemical change or chemical reaction — transformation of one or more atoms or molecules into one or more different molecules.

27. Sure Signs of a Chemical Change • Heat • Light • Gas Produced (not from boiling!) • Precipitate – a solid formed by mixing two liquids together

28. Physical vs. Chemical • physical • chemical • physical • physical • chemical • Examples: • melting point • flammable • density • magnetic • tarnishes in air

29. Physical vs. Chemical • chemical • physical • chemical • physical • physical • Examples: • rusting iron • dissolving in water • burning a log • melting ice • grinding spices

30. PURE SUBSTANCE MIXTURE yes no yes no Is the composition uniform? Can it be chemically decomposed? Colloids Suspensions Matter Flowchart MATTER yes no Can it be physically separated? Homogeneous Mixture (solution) Heterogeneous Mixture Compound Element

31. Types of Mixtures • Variable combination of 2 or more pure substances. Heterogeneous –visibly separate phases Homogeneous – Same throughout

32. Law of Definite Proportions • Joseph Proust (France 1799) • A given compound always contains elements in a certain proportion by mass. (Constant composition).

33. Atoms combine in whole number ratios, so their proportion by mass will always be the same. • Example: H2O is always made up of 2 atoms of H and one atom of O. The mass ratio of O to H in water is always 16:2 or 8:1. Percent Mass of Compounds • Percent composition consists of the mass percent of each element in a compound: Percent by mass=

34. Example: KCl • KCl always contains one atom of K for every one atom of Cl • In KCl, potassium and chlorine always have a ratio of “39.09 to 35.45” or “1.1 to 1” by mass.

35. Law of Multiple Proportions (John Dalton) • When the same two elements combine to form more than one compound: the ratios of the mass of one element in the first compound to its mass in the second compound, (as it combines with the same mass of the other element), can always be expressed as ratios of small whole numbers( ex: 1:3 or 2:5).

36. Example of Law of Multiple Proportions • Carbon combines with oxygen to form CO and CO2 . 12.01 16.00 2:1 12.01 32.00

37. Practice Problem 1 In the carbon compounds ethane (C2H6) and ethene (C2H4), what is the lowest whole number ratio of H atoms that react with the same number of C atoms? 24.02 6.06 6:4 or 3:2 24.02 4.04

38. Mixtures Heterogeneous mixture – Uneven distribution of substances. You can see the different parts. Examples: Sand Granite Wood Suspensions

39. Mixtures Homogeneous Mixture– Components are evenly mixed. - Cannot see the parts. Salt water contains salt and water, but are mixed all the way to the atomic level but it can still be separated by physical means.

40. Homogeneous Solutions • Solute dissolves in solvent to form solution. • Concentrated solution contains more solute than dilute solution. • Small particle size (<2nm) • Can NOT be separated by filtration • Ex: Kool-Aid, iced tea, coffee

41. Solutions A solution is a homogeneous mixture A solute is the substance being dissolved A solvent is dissolving the solute, most commonly a liquid (H2O) Called an aqueous (aq) solution when solvent is H2O Typically, the solute is the component in the smaller amount. Solvent is the component in the larger amount.

42. Types of Solutions • Solution of gaseous solute in gaseous solvent: Air (Oxygen & Nitrogen) • Solution of gas in liquid: Soft drinks (CO2 in water). • Solution of liquid in liquid: Nail polish remover (acetone in water) • Solution of solid in liquid: Salt in water • Solution of solid in solid: Alloys such as steel (a mixture of Fe & C).

43. Separation Methods: Filtration Distillation Crystallization Sublimation Chromatography

44. Filtration Used to separate heterogeneous mixtures composed of solids & liquids Uses a porous barrier (such as filter paper) that allows the liquid to pass through, but no the solid Example: sand and water mixture

45. Distillation Used to separate homogeneous mixtures Based on the differences in the boiling points of the involved substances Mixture is heated until the substance with the lower boiling point boils to a vapor The vapor is then condensed into a liquid and collected Example: distilled water (removes minerals from the water)

46. Crystallization Used to separate substances in solution Results in the formation of highly pure solids As one substance evaporates, the dissolved substance comes out of solution and collects as crystals Example: rock candy, salt water

47. Sublimation Used to separate mixtures of solids One solid sublimes and the other is left behind The gas can then be condensed and collected Example: separating ammonium chloride (NH4Cl) from sand and salt

48. Chromatography Used to separate components that are dissolved in a liquid or a gas Based on the ability of each component to be drawn across the surface of another material When the mixture is a liquid, it is drawn across chromatography paper Separation occurs because the various components travel across the paper at different rates (the stronger attraction to the paper, the slower the rate) Example: forensics: blood levels of toxins after a person’s death

49. What is a property? • Describes a substance (matter) • Can be measured and/or observed • Some can be used to identify a substance Chemical propertyPhysical property observed during a describes matter reaction

50. Intensive Properties of Pure Substances remain the same when a substance changes in size Some can be used to IDENTIFY a pure substance (density, boiling pt., melting pt.)