44 ILLINOIS STATE ACADEMY OF SCIENCE 



building up a system of chemical combination based 

 upon the assumption of indivisible atoms — a system 

 which has proved extremely fruitful in bringing the facts 

 of chemistry, especially organic chemistry, to light and 

 which constitutes one of the most remarkable achieve- 

 ments of human intelligence. Within the last few years, 

 by a series of brilliant experiments, the existence of the 

 atom has been established beyond a doubt. For most of 

 the direct evidence of the existence of the atom we are 

 indebted to the physicist. But the physicist was not 

 content with demonstrating the existence of the atom. 

 He has gone ahead and shown that the atom is made up 

 in turn of electrons and positive nuclei and is of such 

 complexity as to defy our comprehension. His work has 

 proved that both schools of chemists were wrong. Atoms 

 exist, but they are not the hard, indivisible particles that 

 the chemist thought them to be. They are perhaps 

 nothing but systems of electrical particles. These par- 

 ticles themselves are nothing but centers of electrical 

 force. There is nothing left for the man whose imagina- 

 tion works through his tactual sense to rub between his 

 fingers and say, ''This is matter." The man who was 

 happy with hard, indivisible atoms is no more comfort- 

 able with this complicated atom that the physicist has 

 forced upon him than he would have been in the old days 

 without any atoms at all. 



The chemist is interested primarily in the ability of 

 atoms to combine with atoms of other elements to form 

 chemical compounds. The numerical measure of the 

 ability of an atom to combine with other atoms has been 

 called its valence, and the force which binds one atom 

 to another, as to the nature of which we have been until 

 recently very much in the dark, has been designated as 

 the valence bond. By ascribing to hydrogen one valence 

 bond, oxygen two and carbon four, the organic chemist 

 has built up a most extraordinary system of chemical 

 valence which not only applies almost perfectly to sev- 

 eral hundred thousand compounds, but which may al- 

 most be said to predict the existence and the properties 

 of this vast number of compounds as well as innumerable 



