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Re: [Phys-l] macromolecules

Within the field of X-ray crystallography, macromolecules refer to large molecules which remain so in solution. Proteins are macromolecules which yield their structural secrets when crystallized, and illuminated with X-rays which are observed with detectors, a few of which I have spent some years working on. Small molecules are distinguished in the same manner, and the unit cell remains small in the crystalline state.

Quoting John Denker <jsd@av8n.com>:

On 03/03/2010 03:48 PM, Stefan Jeglinski wrote:

... I see MO
as a useful concept "along the way" but I would not have guessed it
to be relevant compared to band structure calculations. Yet you
recommend thinking of a crystal as a macromolecule with HOMO and
LUMO.

You brought it up. Mostly I was just wanted to
go with the flow.

In any case, the crystal *is* a macromolecule. It
upholds the letter and spirit of the IUPAC definition
of molecule, and IMHO any other reasonable definition
of molecule.

Pedagogical remark: Even though identifying the
crystal as a macromolecule is strictly true and
important, the pedagogical value may be small, or
zero, or arguably negative ... because the students
have precious little understanding of macromolecules.

This is a serious dilemma, and the decision of how
to proceed depends on how much time you can devote
to it. The problem is much of what the students
know about chemistry is either irrelevant or outright
wrong when it comes to macromolecules.

The pedagogical principle here is that "learning
proceeds from the known to the unknown". So before
you can apply chemical/molecular terminology and
concepts to semiconductors, you first need to spend
some quality time making sure the students understand
the concepts and can correctly apply them to reeeally
big molecules.

Macromolecules are important! Look around. Look in
any direction except the open sky. What do you see?
Wood, metal, and plastic. Cotton, wool, and polyester
fabrics. Rocks and minerals. Plants and animals.
Macromolecules everywhere! Yet macromolecules are
practically taboo in introductory chemistry. Basic
notions such as the law of definite proportions and
what it means to balance a chemical reaction are
taught in ways that are contradicted by the example
of macromolecules. Of course the concepts can be
repaired, but the repairs are costly and time-consuming.

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Jeff Radtke
Supersaturated Environments
http://www.cloudchambers.com