CHAPTER 



2 



Physical Forces 

 and Chemical Bonds 



INTRODUCTION 



As the current pace of advances in molecular biology and biochemistry 

 accelerates, a detailed understanding of the structure, interactions, and 

 functions of biologically important molecules becomes increasingly neces- 

 sary. This means that the forces involved in chemical reactions must 

 be increasingly taken into account, and this requires detailed information 

 about the nature of the various chemical bonds. Consequently, in this 

 chapter we present the basic physical forces and try to give an idea 

 of how they operate to create the various chemical bonds. Funda- 

 mentally, the study of such matters involves comprehension of the com- 

 plex mathematical apparatus of modern theoretical physics and theo- 

 retical chemistry, and it is impossible to get around this requirement. 

 Nevertheless, almost all scientists have geometrical and mechanical 

 images and models in their minds which guide them in their use of such 

 a mathematical apparatus to the point that these images and models 

 serve as the bases of their "intuition" when considering new problems. 

 These images and models are admittedly limited in scope and accuracy, 

 and each scientist may have his own peculiar set. This writer believes 

 that it is useful for beginning students to acquire some intuitive feelings 

 about such matters even before they acquire the detailed apparatus for 

 understanding the matters. Indeed, in some respects it is only to the 

 extent that today's complexity becomes incorporated into the intellectual 

 equipment of the youth that youth has the capacity to transcend the 

 elders. In this spirit, then, is the following discussion of forces and 

 bonds presented. 



PHYSICAL FORCES 



The difference between Newtonian and quantum physics is of a nature 

 which far transcends their procedural differences. But, for our purposes, 

 we find it useful at this point to look at an aspect of the procedural dif- 

 ferences: the emphasis of Newtonian physics on the concept of force; and 

 the emphasis of quantum physics on the concept of energy. Indeed, it is 

 in great part this shift which permitted physics to provide the basis for 



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