chemical principles visualized: seeing the unseen david a. katz department of chemistry pima...

Chemical Principles Visualized:

Seeing the unseenDavid A. KatzDepartment of ChemistryPima Community CollegeTucson, AZ 85745, USA

Voice: 520-206-6044 Email: dkatz@pima.edu

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