Dispelling Myths and Misconceptions Through the Visualization of Quantum Concepts in General Chemistry

Morton Hoffman,1 Dan Dill,1

Peter Garik,2 Alex Golger1

1) Department of Chemistry

2) School of Education

Boston UniversityBoston, Massachusetts

02215http://quantumconcepts.bu.edu

http://quantumconcepts.bu.edu

QC in some current general chemistry

textbooks

Zumdahl, “Chemical Principles,” 3rd Ed. (1998): Chap. 12

Hill and Petrucci, “General Chemistry,” 2nd Ed. (1999): Chap. 7 & 8

Moore, Stanitski, and Jurs, “Chemistry: The Molecular Science,” (2002): Chap. 7

Brady and Senese, “Chemistry: Matter and Its Changes,” 4th Ed. (2004): Chap. 8

Zumdahl and Zumdahl, “Chemistry,” 5th Ed. (2000): Chap. 7

McMurray and Fay, “Chemistry,” 4th Ed. (2004): Chap. 5

Atkins and Jones, “Chemical Principles,” 3rd Ed. (2005): Chap. 1

Petrucci and Harwood, “General Chemistry,” 7th Ed. (1997): Chap. 9

Brown, et al., “Chemistry: The Central Science,” 10th Ed. (2006): Chap. 6

ACS, “Chemistry,” (2005): Chap. 4

http://quantumconcepts.bu.edu

What topics are presented?

Electromagnetic radiation: behavior of waves, Planck relationship

Photoelectric effect: photons, wave-particle duality

Hydrogen atom: emission spectrum, Bohr model, electron energy levels

Quantum (wave) mechanical model: standing waves, Schrödinger equation, orbitals

Uncertainty principle: where is the electron?

Particle in a box: solutions to the Schrödinger equation, quantized energy levels

Wave functions: radial and angular probability distributions, and 2

Quantum numbers: shells and sub-shells

Orbital shapes and representations: electron density plots, boundary surfaces

Orbital energies: degeneracy and multi-electron atoms

http://quantumconcepts.bu.edu

What attitudes toward QC do students bring

into general chemistry?Fear and loathing from pre-college science courses and the popular culture.

Rumors that it’s about some strange equations and dead, Germanic guys with umlauts in their names.

Concerns that it’s about “mechanics” and other non-inspiring subjects from physics.

http://quantumconcepts.bu.edu

Do students “get it?”

Most are puzzled about the whole thing. Many see it merely as impenetrable mathematics with no relevance to reality.

Some can do the algorithmic “plug-and-chug” calculations without too much difficulty.

A few have a satisfactory conceptual understanding.

A couple are inspired by it and want to learn more.

http://quantumconcepts.bu.edu

Why should we bother with Quantum Concepts?

It is basis for understanding spectroscopy, electronic structure, periodic properties.

It is the essence of nanotechnology, quantum computing . . . the future.

It provides insight into the deeply microscopic (atomic, molecular) world.

It encompasses all of chemistry and is completely interdisciplinary.

http://quantumconcepts.bu.edu

General chemistry students and Quantum

Concepts Quantum Concepts are among the most challenging and unsatisfying topics for students (and instructors).

The quantum world makes no sense to everyday intuition; at best, it’s all mathematics.

Failure to reconcile this intuition with quantum behavior results in deeply seated myths and misconceptions.

Quantum Concepts do not seem to provide useful insights for the rest of general chemistry.

http://quantumconcepts.bu.edu

An e-mail from a chemistry professor at a

four-year college

I certainly find that chapter (Chapter 6, in Brown and LeMay I think) the hardest to teach...because, of course, it's such a skimmed-over thing, without the required mathematics. And then we just “pull out of the hat” things like orbitals and quantum numbers. Once we get into trends and hybridization, things settle down again, but I certainly sense general revolt for a week or two.

http://quantumconcepts.bu.edu

What are some of the prevalent myths and misconceptions about Quantum Concepts?

The electron “waves” as it moves.Through the absorption or emission of light energy, electrons “jump” from one quantum level to another.

Electrons “go around” the atom in a particular quantum state.

Spectral lines represent “energy levels” of the electron.

http://quantumconcepts.bu.edu

More myths and misconceptions

When a “photon” is absorbed, light vanishes; when a “photon” is emitted, light appears.

The “orbital” pictures represent the regions in space in which the electrons move.

The “wavefunction” is a static mathematical representation of the electron in the atom.

http://quantumconcepts.bu.edu

The Resolution: Include Time!

and avoid missed connections

These myths and misconceptions arise

because

time has been left out!

http://quantumconcepts.bu.edu

Incoming general chemistry students and

physics They have a good understanding of the spatial description of waves (wavelength and amplitude).

They have a poor understanding of the temporal description of waves (period and frequency).

They have difficulty linking the spatial and temporal behavior of waves.

They are weak in their understanding of the energetics of waves and the nature of fields.

They generally do not know that EM waves have electric and magnetic fields associated with them.

http://quantumconcepts.bu.edu

Our approach

Learning cycle-based activities: data collection, analysis, extension.

Interactive guided-inquiry software that examines spectroscopy and electron orbital energies.

Interactive graphical renderings of time-dependent atomic orbitals without mathematics!

Visualizations of the beats that correspond to dipole excitations of atoms.

A visual introduction to the selection rules for quantum absorption and emission.

http://quantumconcepts.bu.edu

Guided inquiry software

Used in conjunction with lecture demonstrations, lecture/discussion workshops, lab exercises, and homework.

Project 1: spectroscopy of atomic hydrogen and hydrogen-like ions.

Project 2: introduction to the normal modes of one- (cable) and two-dimensional (square and circular membranes) waves with analogy to the modes of a bound electron.

Project 3: time-dependent behavior of electron orbitals and their interaction with light.

http://quantumconcepts.bu.edu

The Resolution: Include Time!

When time is properly included, three key concepts emerge:

The electron wavefunction does change with time.

Electron density in a specific energy state is nevertheless static: nothing moves, nothing evolves, nothing changes.

The mixing of energy states accounts for all motion, evolution, and change.

http://quantumconcepts.bu.edu

Our Conclusion: Include Time!

Proper treatment of “time” in quantum systems is crucial.

It provides the correct framework on which students can reason about quantum change.

Without this framework, myths and misconceptions are the inevitable consequence.

http://quantumconcepts.bu.edu

Why should students in general chemistry learn

this stuff?

Nature continually undergoes change.

Chemistry is the science of change. Time dependence in the quantum world is the analogue for all change in chemistry.

Quantum time dependence is the basis for students to learn how and why things happen.

http://quantumconcepts.bu.edu

Acknowledgements

Peter Carr, Programmer Joshua Csehak and Lars Travers, Ace Coders Programming

Judith Kelley, Project Evaluator Funding, U.S. Department of Education Fund for the Improvement of Post Secondary Education (FIPSE Grant P116B020856)