Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Re: [Phys-l] Definition of Substance



On 03/21/2009 08:50 AM, LaMontagne, Bob wrote:
Why do science educators make up these idiotic narrow definitions of
comon terms. My encyclopedia uses substance to distinguish between
what makes up the physical essence of something versus merely is
form or other attributes. Substance simply means "stuff". We sound
like total jerks when we go around correcting students for using
words the way 99 percent of the rest of the world uses them.

Agreed!

Why do science educators make up these idiotic narrow definitions of
comon terms.

I can tell you exactly where this comes from. It comes from
macroscopic chemistry. A very great deal of the material that
is taught in high-school chemistry (and sometimes introductory
college chemistry) was worked out before 1900, i.e. before there
was any serious understanding of atoms. Working this out was
truly a tour de force.

In particular there was (and is) a macroscopic notion of "element"
and a macroscopic notion of "compound". There was (and is) also
a macroscopic motion of "mole" as -- you guessed it -- amount of
substance. Most physicists think of a mole as just a number, in
the same way that a dozen is just a number ... but this is *not*
how SI and IUPAC define it. In SI, a mole is one of the base
units, expressing the "unit amount of substance". I am not making
this up!
http://www.bipm.org/en/si/si_brochure/chapter2/2-1/mole.html

My reaction to all this is to say that the 1800s have been over
for a while now; wake up and smell the atoms.

We can replace the archaic view with the modern view as follows.
These are not equivalences, but upgrades:
element --> atom
compound --> molecule
mole as amount of substance --> mole as number (like dozen)

There is work in progress, laying the groundwork for redefining
the mole as a number, but official redefinition has not happened
yet. If/when this happens, "substance" will no longer be a required
part of the SI vocabulary.

Meanwhile, chemistry texts and chemistry courses continue to teach
the pre-1900 view of the world. Presumably this is because they
believe in the "historical approach" as a method for organizing
and motivating the study of science. Apparently they think that
pedagogy must recapitulate phylogeny.

This is part of a package including
-- element / compound / mole as amount of substance,
-- significant figures,
-- distinguishing chemical change from physical change
based on simple macroscopic observations,
-- Bohr atoms,
-- Lewis dot diagrams,
-- The principle that "like dissolves like",
-- oxidation numbers,
-- thermodynamics without entropy,
-- et cetera.

Sometimes people wonder why students seem to be lacking in the ability
to think. I'll tell you why: In general, as William James pointed
out, thinking involves forming connections between new things and
previously-learned things. In this case, it is pointless to think
about things that cannot possibly be reconciled with the known facts.