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Definition of Atom
Name: Marcel
Status: other
Age: N/A
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Date: N/A
Question:
I have been teaching my students
that an atom (or molecule) is the smallest
constituent that you can divide a substance into
while maintaining its physical properties. I now
read that some materials on the micron or smaller
scales have dramatically different properties such
as color, boiling point, melting point, etc. I am
trying to keep current with the advances in
materials science to deliver correct information in
my classroom. As we incorporate more nanoscience, I
am becoming a bit worried about my understanding of
basic definitions.
Replies:
Marcel,
I think that the "original definition", that is, "an atom is
the smallest constituent that you can divide a substance into
while maintaining its physical properties", was really never
a particularly good one. Exceptions easily come to mind. As
an example of color, it has been known for centuries that if
one rolls gold into thin sheets, its color becomes green.
Carbon, as diamond and graphite has two entirely different
colors (clear and black). If one considers a single atom,
"melting point" and "boiling point" have never had any
meaning. As for general properties, many physical properties
depend on the way individual atoms are grouped together, into
(for example) crystals. But this is complicated by some
elements such as carbon or sulphur that have several radially
different crystal structures, so not only do we often have
conflicting physical properties for the same element, we have
the problem that a crystal's properties depend on there being
more than one atom of the element.
A better definition is that an atom is the smallest component
of an element that not only can maintain that element's basic
chemical properties, it is the smallest component of an
element that has any chemical properties at all! Remember
that all of an element's chemical and most of its physical
properties are determined only by its electron shells.
Without the electrons, the remaining nucleus has no chemical
properties at all.
Regards,
Robert Wilson
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Update: June 2012
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