Ask A Scientist Chemistry Archive

From:       bad
Text:       In a class yesterday, a student asked, "If molecules are so small 
that we cannot see them with a microscope, how do we know they exist?"  The 
teacher could not respond with an answer nor could I.  How do we know that 
molecules exist?

Response #:  1 of 2
Author:      Joe Schultz
Text:        We do not.  But there is enough evidence to support the fact that 
matter has to be made of something and molecules are the best explanation.  
Physicists have proven the existence of many of the elements through particle 
acceleration studies.  By combining these elements, something has to be 
formed...molecules are what we call them.  If someone can prove that anything 
is made of something other than a chemical (or does not involve a chemical), I 
believe the American Chemical Society has a million dollars for you!  P-
chemists...your turn.

Response #:  2 of 2
Author:      Robert Topper
Text:        Okay Joe....as a p-chemist I claim that molecules have indeed 
been seen with a microscope!  The technique is called "scanning tunneling 
microscopy."  Actually, I should not say THE technique; atoms have also been 
observed with atomic for microscopes.  So the problem is not that atoms and 
molecules cannot be seen with a microscope; they just cannot be seen with an 
AFFORDABLE microscope (the methods above are only practical for research 
laboratories to use).  However, even before this there was lots of good 
evidence for the existence of molecules. If you hit a crystal with a beam of 
rays, the rays diffract into patterns which can be used to tell exactly where 
the atoms in the crystal are located.  This technique, which was proposed by 
Sir William Bragg in the late 1800's, only works if matter is made of atoms.  
So the students can look in issues of Science, Nature, etc. and see the 
aforementioned pictures of atoms and molecules on surfaces.  If this does not 
satisfy them, well, I think they should go to college, study hard, and then 
start doing some experiments themselves!  They are asking good questions, that 
is for sure.