chemical principles visualized: seeing the unseen
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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 Email: [email protected] Web site: www.chymist.com. Chemistry is “hard”!. Technical vocabulary - PowerPoint PPT PresentationTRANSCRIPT
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Chemical Principles Visualized:
Seeing the unseenDavid A. KatzDepartment of ChemistryPima Community CollegeTucson, AZ 85745, USA
Voice: 520-206-6044 Email: [email protected]
Web site: www.chymist.com
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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
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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.
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• 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.
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Learning needs to be multisensory
Not this:
This:
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• 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
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• 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.
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These occur early in the textbook.Little explanation is given.
Single particle “atoms” are easy to understand, water is more difficult.
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Concept is good, but students do not understand the “open” structure of ice as compared with liquid water
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• 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.
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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
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Molecular Shapes Modeling clay and toothpicks to build shapes
MX2 – linear, 180° bond angle
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Molecular Shapes
MX3 triangular planar (trigonal planar) 120° bond angle
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Molecular Shapes
MX4 tetrahedral,109.5° bond angle
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Molecular ShapesMolecules with non-bonded electron pairs
Trigonal pyramid, 107.5° bond angle
Bent104.5° bond angle
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Roy Tasker, et. al., VisChem Molecular -Level Visualization Tool
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LABORATORY EXPERIMENTSand CLASS ACTIVITIES
The Scientific Method1. Observation/Event2. Hypothesis3. Experiment4. Communication/Publication5. Research Grant6. Experiment7. Theory?8. Verification/modification of theory----------------------------9. Physical Law
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The Scientific MethodHypothesis 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?
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Scientific MethodMystery 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.
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The Electromagnetic Spectrum
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X-Rays
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Visible LightAn overhead projector spectroscope
Holographic diffraction grating
Slit and colored filters
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Colored Flames
Strontium – redStrontium – redLithium - redLithium - redCalcium – red/orangeCalcium – red/orangeCopper – green or blueCopper – green or blueBarium – yellow-greenBarium – yellow-greenPotassium – violetPotassium – violetSodium - yellowSodium - yellow
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The Electromagnetic Spectrum
How do we identify elements in space?
Build a spectroscope:Identify elements using spectrum tubesFind elements in yourenvironment
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The Visible Electromagnetic Spectrum
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Density
Indiana Jones – Raiders of the Lost Ark
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Coke vs. Diet Coke
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Hot and ColdSeparate water by density
COLD HOT
HOT
COLD
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Chemical Formulas and Nomenclature
Formula cards – polyatomic ions treated as single units
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Chemical ReactionsWhat factors indicate a chemical reaction occurred?
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The Synthesis of Zinc Iodide: Tracking a Chemical Reaction
Test properties of powdered zincTest properties of iodineMix zinc and iodine in a petri dish Place in a zip-lock bagAdd waterFilter resulting solutionTest properties of solutionEvaporate to drynessAdd water and test properties of solutionExplain what happenedWrite balanced equation
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The Activity SeriesGroup I
Group II
Group III
Transition elements
Group IV
Hydrogen
Group IB (jewelry and tooth fillings)
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Intermolecular forces Drops of water on a coin
How many drops of water can you put on a coin? Why?
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1. Intermolecular forces using I2
1. Iodine vapor2. Iodine-hexane:
Nonpolar interactions (London forces)
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2. Intermolecular forces using I2
Dipole - Induced dipole
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3. Intermolecular forces using I2
Ion – induced dipole
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4. Intermolecular forces using I2
Solubility preference:Like dissolves like Hexane
layer
Water layer
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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
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Acids and Bases• 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
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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 1 pH 7 pH 14strong weak neutral weak strong acid acid base base The pH scale according to the late Dr. Hubert Alyea, Princeton University
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pH values for some common
substances
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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
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Colloids• Tyndall effect
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Why is the sky blue?Normal sky color
Pale blue sky near horizon
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Course syllabi and experimentscan be found at
http://www.chymist.com
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