PAPERS PRESENTED AT GENERAL SESSIONS 45 



other compounds which yet await syntheses in the 

 laboratory. 



When we come to inorganic chemistiy, the situation 

 is different. In the first place, the valence of many of the 

 elements is not a simple, definite number, but is a vari- 

 able quantity, some of the elements having as many as 

 seven different numerical valences. In the second place, 

 the valence bond is a different sort of a thing than the 

 one we met in organic chemistry. If we electrolyze sodium 

 chloride which has been brought into a liquid condition 

 by solution or melting, the sodium travels in the direc- 

 tion of the positive current, and the chlorine in the oppo- 

 site direction, thus demonstrating that the sodium atoms 

 are positively charged and the chlorine atoms negatively 

 so. It has been recognized since the time of Faraday 

 that the attraction of the- positively charged sodium 

 atom for the negatively charged chlorine atom would 

 account fully for the valence bond in sodium chloride. 

 It remained for the brilliant researches of Bragg and 

 Bragg to show just how and why this was so. Physical 

 experiments show that a sodium chloride crystal is made 

 up of alternate positive and negativ-e charges arranged 

 in a so-called simple cubic arrangement, each positive 

 charge surrounded by six negative charges, and each 

 negative charge surrounded by six positives. These 

 charges are not to be confused with the electron or ele- 

 mentary positive charge, however. For with the posi- 

 tive charge is associated a mass equal to that of the 

 sodium atom and with the negative charge a mass equal 

 to that of the chlorine atom. Evidently, then, we have 

 the charged atoms acting as indivisible units and bound 

 to each other by electrostatic forces alone. In valence 

 bonds of this nature, therefore, number has lost its sig- 

 nificance, for apparently one sodium atom may attract 

 the six chlorine atoms which surround it with as much 

 force as it would attract a single chlorine atom in a 

 sodium chloride molecule in the gaseous state. Evident- 

 ly, therefore, if we were to try to write sodium as we do 

 carbon, oxygen and hydrogen in organic chemistry, with 

 a certain number of dashes to represent its valence, we 



