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Chemical Principles Visualized: Seeing the unseen David A. Katz Department of Chemistry Pima Community College Tucson, AZ 85745, USA Voice: 520-206-6044.

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Presentation on theme: "Chemical Principles Visualized: Seeing the unseen David A. Katz Department of Chemistry Pima Community College Tucson, AZ 85745, USA Voice: 520-206-6044."— Presentation transcript:

1 Chemical Principles Visualized: Seeing the unseen David A. Katz Department of Chemistry Pima Community College Tucson, AZ 85745, USA Voice: Web site:

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:

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:

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 Shapes Using 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 Teach shapes BEFORE Lewis dot structures

12 Molecular Shapes Modeling clay and toothpicks to build shapes MX 2 – linear, 180° bond angle Characteristic of Periodic Table Group IIA

13 Molecular Shapes MX 3 triangular planar (trigonal planar) 120° bond angle Characteristic of Periodic Table Group IIIA

14 Molecular Shapes MX 4 tetrahedral 109.5° bond angle Characteristic of Periodic Table Group IVA Students must physically form a 3-D structure

15 Molecular Shapes Molecules with non-bonded electron pairs Trigonal pyramid 107.5° bond angle Characteristic of Periodic Table Group VA Bent 104.5° bond angle Characteristic of Periodic Table Group VIA

16 Students can build some models using The Molecular Level Visualization Tool Roy Tasker, et. al.,

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18 LABORATORY EXPERIMENTS and CLASS ACTIVITIES The Scientific Method 1.Observation/Event 2.Hypothesis 3.Experiment 4.Communication/Publication 5.Research Grant 6.Experiment 7.Theory? 8.Verification/modification of theory Physical Law

19 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?

20 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.

21 The Electromagnetic Spectrum

22  Rays

23 X-Rays

24 UV Light Uranium glass Tide laundry detergent

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

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

27 The Electromagnetic Spectrum Viewing spectra using holographic diffraction grating (Flinn Scientific C-Spectra) Hydrogen spectrum Helium spectrum

28 The Electromagnetic Spectrum How do we identify elements in space? Build a spectroscope: In class: Identify elements using spectrum tubes Homework: Find elements in your environment

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

30 Infrared Light

31 Microwaves

32 Radio Waves

33 The Visible Electromagnetic Spectrum

34 Optical Rotation An optically active compound can rotate light Due to an asymmetrical carbon atom (carbon bonded to 4 different groups) Enantiomers: molecules are mirror images of themselves Solutions of the D- isomer twists the light clockwise; L-isomer twists light counter-clockwise Dextrose (d-glucose) solution in polarized light on an overhead projector

35 Density Indiana Jones – Raiders of the Lost Ark

36 Coke vs. Diet Coke

37 Hot and Cold Separate water by density COLD HOT HOT COLD

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

39 Chemical Reactions What factors indicate a chemical reaction occurred?

40 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

41 Chemical Reactions Visualizing reaction stoichiometry CH 4 + O 2  CO 2 + H 2 O 

42 Chemical Reactions Visualizing reaction stoichiometry CH O 2  CO H 2 O 

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

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

45 1. Intermolecular forces using I 2 1.Iodine vapor 2.Iodine-hexane: Nonpolar interactions (London forces)

46 2. Intermolecular forces using I 2 Dipole - Induced dipole

47 3. Intermolecular forces using I 2 Ion – induced dipole

48 4. Intermolecular forces using I 2 Solubility preference: Like dissolves like Hexane layer Water layer

49 Intermolecular Forces: Which Will Evaporate First? What factors affect evaporation? Spread these compounds on black chalkboards Water methanol ethanol 2-propanol Effect of molecular weight: H 2 O = 18 CH 3 OH = 32 C 2 H 5 OH = 46 C 3 H 8 OH = 60 Effect of polarity

50 Visualizing Equilibrium Students start with 2 containers of colored water, mL beakers, and mL graduated cylinders One student switches to a 150-mL beaker while the second student uses a 400-mL beaker, and continues the process

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

52 pH First introduced by Danish chemist Søren Peder Lauritz Sørensen ( ), 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 1 pH 7 pH 14 strong weak neutral weak strong acid acid base base The pH scale according to the late Dr. Hubert Alyea, Princeton University

53 pH values for some common substances

54 Acids, Bases, and pH Acids, bases, and pH using red cabbage paper – Buffers for reference – Solutions of household products to spot the paper – mL of solution can serve 100 students Illustrate indicator colors using serial dilutions of strong acids and bases to observe color changes

55 Colloids Tyndall effect

56 Why is the sky blue? Normal sky color Pale blue sky near horizon

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58 Course syllabi and experiments can be found at On the left-hand menu, click on Compleat Chymical Demonstrator or Magic Into Science or, for course information and experiments, Pima Chem Courses then click on appropriate course link: Chem 121, Chem 125, Chem 130, Chem 151, or Chem 152


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