METALS AND METALLOIDS 703 



metals. The tendency for these metals to unite with hydro- 

 carbon radicals is very slight. Organic derivatives of sodium 

 and potassium were indicated by Frankland and Wanklyn 

 but not isolated as individual compounds. Here, as in the 

 case of magnesium, residual affinity plays an important part 

 in increasing the stability of the organic derivatives. Sodium 

 ethyl, although not isolated as such, has been obtained in an 

 additive compound with zinc ethyl containing the two metals in 

 atomic proportions, Na . C 2 H 5 , Zn(C 2 H 5 ) 2 . 



The metals of the alkalis resemble those of the alkaline 

 earths as regards their feeble affinity for hydrocarbon radicals. 



(e) The Gold-Platinum Group 



Alternating with the alkali metals in the first vertical series, 

 we find the currency metals, copper, silver, and gold. Although 

 researches are even now in progress, only one of these, namely 

 gold, has been definitely combined with hydrocarbon groups. 

 This combination was successfully accomplished by Pope and 

 Gibson in 1907, by acting on auric bromide with the Grignard 

 reagent, magnesium ethiodide : 



AuBr 3 + 2MgC 2 H 6 I = Au(C 2 H 5 ) 2 Br + Mgl 2 + MgBr 2 . 



The product, diethylauric bromide, which was obtained in 

 colourless needles, reacted with bromine to yield ethylauric 

 dibromide, Au(C 2 H 5 )Br 2 , a ruby-red crystalline compound com- 

 bining additively with ammonia, and in this respect resembling 



boron trimethyl : 



NH,s /Br 



Au(C 2 H g )Br 2 + NH 3 = >Au< 



C 2 H/ \Br 



In this reaction the general tendency to form the compound with 

 four associating units is again apparent. 



The metal platinum, closely allied in many respects to gold, 

 occurs in the periodic scheme as the final member of the metals 

 of the eighth vertical series, which contains nine metals arranged 

 in three sets each with three members. Pope and Peachy have 

 successfully applied the Grignard reagent to platinic chloride 

 dissolved in dry ether : 



PtCU + 3 Mg(CH 3 )I = (CH 3 ) s PtI + Mgl 2 + 2 MgCl 2 . 



Trimethylplatinic iodide (bright yellow crystals) is con- 

 verted by moist silver oxide into trimethylplatinic hydroxide 



