Chemical Principles Visualized: Seeing the unseen

1. Chemical Principles Visualized: Seeing the unseen David A. Katz Department of Chemistry Pima Community College Tucson, AZ 85745, USA Voice: 520-206-6044 Email: dkatz@pima.edu Web site: www.chymist.com

2. Chemistry is “hard”! • Technical vocabulary • Concepts and abstractions – difficult to relate to everyday • Difficult to visualize electrons, atoms, molecules, reactions, etc… • Cannot memorize information – must have some degree of understanding • Boring lectures (“chalk talks”) with a lot of information (information overload) • Requires math

3. Chemistry is Fun! • Chemistry, as an experimental science, is not just an intellectual pursuit, but, a hands-on (or “hands-in”) science. • Through chemistry we can create a wondrous range of substances and materials with unique colors, odors, and properties. • None of the physical or natural sciences are as creative as chemistry.

4. Students, on the average, have little or no concrete concepts or experiences of the phenomena described in a college chemistry course. • Even with prep courses, typical instructors just talk about chemistry and chemical reactions. • Students cannot think in 3-D. • Students have limited visualization skills • Pictures may help • Videos are better • Live demonstrations and hands-on activities in the classroom enhance the learning of concepts.

5. Learning needs to be multisensory Not this: This does not work This: Visualize Touch Smell Think

6. At the 14th International Conference on Chemical Education, University of Queensland, Brisbane, Australia, July 14-19, 1996, Roy Tasker, Bob Bucat, Ray Sleet and Bill Chia, unveiled molecular-level animations which are known as the VisChem project. Tasker, R. & West, T. with Lockyer, L. & Harper, B. (2002). Chemistry Molecular Level Construction Tool. Retrieved August 16, 2009 , from Learning Designs Web site: http://www.learningdesigns.uow.edu.au/tools/info/T4/index.html

7. Modern textbooks are now employing macro-to-micro diagrams and animations of “molecules” are also available. • These diagrams, often presented early in a textbook, precede discussions of chemical bonding and molecular geometries, as well as the chemical interactions they may represent. • Not only must students be trained in understanding these diagrams, but they need to experience the actual phenomena being depicted.

8. These occur early in the textbook. Little explanation is given. Single particle “atoms” are easy to understand, water is more difficult.

9. Concept is good, but students do not understand the “open” structure of ice as compared with liquid water

10. This is better. • It shows the student a progression of formula representations. • At this point in the course, shapes have little or no meaning to students. • Also, students are not familiar with ball-and-stick vs space filling models.

11. Molecular ShapesUsing Modeling Clay and Toothpicks • The shape of a molecule plays an important role in its reactivity. • Students cannot think in 3-D • Manipulating “atoms” into molecular shapes formalizes VSEPR

12. Molecular Shapes Modeling clay and toothpicks to build shapes MX2 – linear, 180° bond angle

13. Molecular Shapes MX3 triangular planar (trigonal planar) 120° bond angle

14. Molecular Shapes MX4 tetrahedral, 109.5° bond angle

15. Molecular Shapes Molecules with non-bonded electron pairs Trigonal pyramid, 107.5° bond angle Bent 104.5° bond angle

16. Roy Tasker, et. al., VisChem Molecular -Level Visualization Tool

19. LABORATORY EXPERIMENTSand CLASS ACTIVITIES The Scientific Method • Observation/Event • Hypothesis • Experiment • Communication/Publication • Research Grant • Experiment • Theory? • Verification/modification of theory ---------------------------- 9. Physical Law

20. The Scientific Method Hypothesis and Experiment 4 cards Each has a number on one side and a letter on the other side. Two letters showing, two numbers showing Hypothesis: Any card with a vowel (A, E, I, O, U) on one side has an even number (0, 2, 4, 6, 8) on the other side. Question: How many cards must we turn over to prove (or disprove) the hypothesis?

21. Scientific Method Mystery powders: How to do an investigation • 4 white powders: • Salt • Starch • Powdered sugar • Baking soda • 3 liquids: • Water (w) • Vinegar (v) • Iodine solution (i) • Unknown mixtures of 2 or 3 powders • Identify by properties only.

22. The Electromagnetic Spectrum

23. X-Rays

24. Visible Light An overhead projector spectroscope Holographic diffraction grating Slit and colored filters

25. Colored Flames Strontium – red Lithium - red Calcium – red/orange Copper – green or blue Barium – yellow-green Potassium – violet Sodium - yellow

26. How do we identify elements in space? • Build a spectroscope: • Identify elements using • spectrum tubes • Find elements in your • environment The Electromagnetic Spectrum

27. The Visible Electromagnetic Spectrum

28. Density Indiana Jones – Raiders of the Lost Ark

29. Coke vs. Diet Coke

30. Hot and Cold Separate water by density COLD HOT HOT COLD

31. Chemical Formulas and Nomenclature Formula cards – polyatomic ions treated as single units

32. Chemical Reactions What factors indicate a chemical reaction occurred?

33. The Synthesis of Zinc Iodide: Tracking a Chemical Reaction Test properties of powdered zinc Test properties of iodine Mix zinc and iodine in a petri dish Place in a zip-lock bag Add water Filter resulting solution Test properties of solution Evaporate to dryness Add water and test properties of solution Explain what happened Write balanced equation

34. The Activity Series Group I Group II Group III Transition elements Group IV Hydrogen Group IB (jewelry and tooth fillings)

35. Intermolecular forces Drops of water on a coin How many drops of water can you put on a coin? Why?

36. 1. Intermolecular forces using I2 • Iodine vapor • Iodine-hexane: Nonpolar interactions (London forces)

37. 2. Intermolecular forces using I2 Dipole - Induced dipole

38. 3. Intermolecular forces using I2 Ion – induced dipole

39. 4. Intermolecular forces using I2 • Solubility preference: • Like dissolves like Hexane layer Water layer

40. Intermolecular Forces:Which Will Evaporate First? What factors affect evaporation? Water methanol ethanol 2-propanol Effect of molecular weight: H2O = 18 CH3OH = 32 C2H5OH = 46 C3H8OH = 60 Effect of polarity

41. Acids andBases • Svante August Arrhenius (1859 –1927) • Acid produces hydrogen ions in water solution. • Johannes Nicolaus Brønsted (1879-1947) and Thomas Martin Lowry (1874-1936) • An acid-base reaction consists of the transfer of a proton (or hydrogen ion) from an acid to a base

42. pH • First introduced by Danish chemist Søren Peder Lauritz Sørensen (1868-1939), the head of the Carlsberg Laboratory’s Chemical Department, in 1909 • pH means ‘the power of hydrogen’. • Each value of pH means the H+ concentration changes by a factor of 10 • As the H+ concentration decreases, the OH- concentration increases pH 1pH 7pH 14 strong weak neutralweak strong acid acidbase base The pH scale according to the late Dr. Hubert Alyea, Princeton University

43. pH values for some common substances

44. Acids, Bases, and pH • Acids, bases, and pH using red cabbage paper • Buffers for reference • Solutions of household products • Illustrate indicator colors using serial dilutions to observe color changes

45. Colloids • Tyndall effect

46. Why is the sky blue? Normal sky color Pale blue sky near horizon

48. Course syllabi and experimentscan be found athttp://www.chymist.comOn the left-hand menu, click on CompleatChymical Demonstrator or Magic Into Scienceor, for course information and experiments, Pima Chem Coursesthen click on appropriate course link:Chem 121, Chem 125, Chem 130,Chem 151, or Chem 152