chemical principles visualized: seeing the unseen david a. katz department of chemistry pima...
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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
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
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.
• 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.
Learning needs to be multisensory
Not this:
This:
• 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
• 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.
These occur early in the textbook.Little explanation is given.
Single particle “atoms” are easy to understand, water is more difficult.
Concept is good, but students do not understand the “open” structure of ice as compared with liquid water
• 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.
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
• Teach shapes BEFORE Lewis dot structures
Molecular Shapes Modeling clay and toothpicks to build shapes
MX2 – linear, 180° bond angle
Characteristic of Periodic Table Group IIA
Molecular Shapes
MX3 triangular planar (trigonal planar)
120° bond angleCharacteristic of Periodic Table Group IIIA
Molecular Shapes
MX4 tetrahedral
109.5° bond angleCharacteristic of Periodic Table Group IVAStudents must physically form a 3-D structure
Molecular ShapesMolecules with non-bonded electron pairs
Trigonal pyramid 107.5° bond angleCharacteristic of Periodic Table Group VA
Bent104.5° bond angle
Characteristic of Periodic Table Group VIA
Students can build some models using The Molecular Level Visualization ToolRoy Tasker, et. al., http://www.learningdesigns.uow.edu.au/tools/info/T4/index.html
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
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?
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.
The Electromagnetic Spectrum
Rays
X-Rays
UV Light
Uranium glass
Tide laundry detergent
Visible LightAn overhead projector spectroscope
Holographic diffraction grating
Slit and colored filters
Visible LightAn overhead projector spectroscope
Holographic diffraction grating
Slit and colored filters
The Electromagnetic Spectrum
Viewing spectra using holographic diffraction grating (Flinn Scientific C-Spectra)
Hydrogen spectrum Helium spectrum
The Electromagnetic Spectrum
How do we identify elements in space?
Build a spectroscope:In class: Identify elements using spectrum tubesHomework: Find elements in your environment
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
Infrared Light
Microwaves
Radio Waves
The Visible Electromagnetic Spectrum
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
Density
Indiana Jones – Raiders of the Lost Ark
Coke vs. Diet Coke
Hot and ColdSeparate water by density
COLD HOT
HOT
COLD
Chemical Formulas and Nomenclature
Formula cards – polyatomic ions treated as single units
Chemical ReactionsWhat factors indicate a chemical reaction occurred?
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
Chemical ReactionsVisualizing reaction stoichiometry
CH4 + O2 CO2 + H2O
Chemical ReactionsVisualizing reaction stoichiometry
CH4 + 2 O2 CO2 + 2 H2O
The Activity SeriesGroup I
Group II
Group III
Transition elements
Group IV
Hydrogen
Group IB (jewelry and tooth fillings)
Intermolecular forces Drops of water on a coin
How many drops of water can you put on a coin? Why?
1. Intermolecular forces using I2
1. Iodine vapor2. Iodine-hexane:
Nonpolar interactions (London forces)
2. Intermolecular forces using I2
Dipole - Induced dipole
3. Intermolecular forces using I2
Ion – induced dipole
4. Intermolecular forces using I2
Solubility preference:Like dissolves like Hexane
layer
Water layer
Intermolecular Forces:Which Will Evaporate First?
What factors affect evaporation? Spread these compounds on black chalkboards
Water methanol ethanol 2-propanolEffect of molecular weight:
H2O = 18 CH3OH = 32 C2H5OH = 46 C3H8OH = 60
Effect of polarity
Visualizing Equilibrium
Students start with 2 containers of colored water, 2 400-mL beakers, and 2 500-mL graduated cylinders One student switches to a 150-mL beaker while the second student uses a 400-mL beaker, and continues the process
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
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
pH values for some common
substances
Acids, Bases, and pH
• Acids, bases, and pH using red cabbage paper– Buffers for reference– Solutions of household
products to spot the paper– 5 -10 mL of solution can
serve 100 students
• Illustrate indicator colors using serial dilutions of strong acids and bases to observe color changes
Colloids• Tyndall effect
Why is the sky blue?Normal sky color
Pale blue sky near horizon
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