Transcript PowerPoint Presentation - Dispelling Myths and

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 University
Boston, Massachusetts 02215
http://quantumconcepts.bu.edu
QC in some current general
chemistry textbooks
Zumdahl, ÒChemical Principles,Ó 3rd Ed. (1998): Chap. 12
Hill and Petrucci, ÒGeneral Chemistry,Ó2nd Ed. (1999) : Chap. 7 & 8
Moore, Stanitski, and Jurs, ÒChemistry: The Molecular Science,Ó (2002): Chap. 7
Brady and Senese, ÒChemistry: Matter and Its Changes,Ó 4th Ed. (2004) : Chap. 8
Zumdahl and Zumdahl, ÒChemistry,Ó5th Ed. (2000) : Chap. 7
McMurray and Fay, ÒChemistry,Ó4th Ed. (2004) : Chap. 5
Atkins and Jones, ÒChemical Principles,Ó 3rd Ed. (2005) : Chap. 1
Petrucci and Harwood, ÒGeneral Chemistry,Ó7th Ed. (1997): Chap. 9
Brown, et al. , ÒChemistry: The Central Science,Ó 10th Ed. (2006) : Chap. 6
ACS, ÒChemistry,Ó(2005): Chap. 4
http://quantumconcepts.bu.edu
What topics are presented?
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
These myths and
misconceptions arise
because
time has been left out!
The Resolution:
Include Time!
and avoid missed
connections
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)
http://quantumconcepts.bu.edu