METALS AND METALLOIDS 697 



perty forms the distinctive family trait for this group of elements, 

 in which we may, by straining a point, include carbon, since 

 this element is known to possess in the highest degree the 

 property of combining with hydrocarbon radicals. Hence the 

 fourth vertical series of the periodic scheme may be divided 

 into two families, the former of which yields organic derivatives 

 but the latter does not : 



Silicon family . C Si Ge Sn Pb 



Titanium family . Ti Zr Ce Th 



It will be sufficient to consider the following two series of 

 alkyl derivatives to see the family likeness of the five members 

 of the silicon family : 



The first member of the series, C(CH 3 ) 4 , regarded from our 

 present standpoint as an organic derivative of carbon, is a 

 hydrocarbon of the paraffin series, but it does not occur in 

 mineral oils. Like its homologues, the organo-metallic com- 

 pounds of tin and lead, it is produced through the agency of 

 zinc methyl, the other reagent in this instance being the 

 dichloride of the well-known solvent acetone, (CH 3 ) 2 CO : 



(CH 3 ) 2 CC1 2 + Zn(CH 3 ) 2 = ZnCl 2 + C(CH 3 ) 4 . 



Similarly silicon tetramethyl and tetrethyl are produced by 

 the interaction of zinc alkyls and silicon tetrachloride. Tin 

 tetramethyl is obtained from methyl iodide and an alloy of 

 tin and sodium. Lead tetramethyl and tetrethyl are prepared 

 by the general process from the zinc alkyls and lead chloride. 

 It is interesting to note the exaltation in the valency of lead 

 produced in these condensations : 



II. IV. 



2 PbCl 2 + 2Zn(CH 3 ) 2 = Pb + 2ZnCl 2 + Pb(CH 3 ) 4 . 



Silicon, tin, and lead yield also organic derivatives containing 

 aryl radicals. 



By surrounding silicon or tin with four dissimilar radicals, 

 three being organic groups, it has been demonstrated that the 

 product is a racemic combination containing two optically active 

 components related to one another as object and image. 



