Atom and Molecule Properties
Date: Around 1999
I had a question about chemistry and am searching the
internet for an answer.
I was wondering if you could be of any help.
Knowing the properties of all of the atoms,
can properties of molecules be calculated from this knowledge,
or are molecular properties inheritant to the molecule itself.
For example: can the melting and boiling points
for say methane or butane be calculated just knowing
the all of the properties of C and H???
Unfortunately, the individual properties of an atomic species do not
reflect the properties of the molecule.
The example of hydrogen and oxygen, forming water is perhaps a benchmark
for your question.
Molecular properties are inherent to the molecule. They do depend on what
atoms are in the molecule, but just knowing the properties of the free atoms
doesn't tell you everything about the molecule.
The example you give, of melting and boiling points, actually confuses the
issue. These are not molecular properties, but properties of a large
collection of molecules. You can't know the melting and boiling points even
if you know everything about the individual molecules. Those properties
depend on how different molecules interact with each other.
Richard E. Barrans Jr., Ph.D.
PG Research Foundation, Darien, Illinois
The answer is that molecular properties are quite distint
from atomic properties in general. The calculation you
suggest would not work.
Properties of unknown compounds can be predicted somewhat (differing
degrees of success, depending on complexity) just by their structure. But
you need to know how the atoms are arranged, not just what atoms are there.
Donald Yee Ph.D.
San Francisco Estuary Institute
180 Richmond Field Station
1325 South 46th St. Richmond, CA 94804
Click here to return to the Chemistry Archives
Update: June 2012