A Lecture Demonstmtion in Allotropy R. J. FRADEN New York University, New York City'
THE r l r n ~ r n tnntimtn~yhns
f m ~ rk n o ~ m allotropes: I . l ~ r l l o ~Anliniony. r~ This is nnnlogow to yellow nwenie m c l white phosphorus. I t is trawpnrent nnd s o l ~ ~ hin l e C'S.. I t is prrpnrwl hy the nrtim of oxygen i t i l i I I It is w r y un~tnhle on i nnd d ~ n n c r srvrn : ~ t low trrnwrnturrs 10 the h h r k
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of nn nntimono~uhnlidc using n high crlrrellr rlel~sity. I t chnnpes "explosively" to t l ~ emetallic form wit11 the evolution of 2.4 kg.-cnl. per gram atom when hentecl to ZOO0, srrntchel, or strurk. X-ray diqrnms show it t o he in the amorphous stntc,'ancl it nI\v:~ysc o ~ ~ t nsome i~~s occlndwl 11nliclr.a This form is metnstshle r~nderall conditions. The "explosion" is the rrsdt of the hent, prorlt~rwlwhen the nnlorphous antimonv kc-onm cry* tnlline, vn~orizinr . . the occluded hnli(le. thus causine..the fractuhnR'anrl slipht srattcring of the metal. I he nmorphous variety of nntimony may be u . d to demonstrnte n number of phenomena, among which nre: that nn element mny exist in severnl allr~tn~pic morlificntions; thnt enercy is liberatwl (or nh-nr11cd) in the conversion of one allotrope to another; : I I I ~of COUTSB the fnct that there nre several allotrope* ni nntimony. The second of t,hese is belie\-ell hy the author to bc the mo%t significnnt. Although we tell our students thnt such relationships as
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+ .....o..,.,
P W ~#I PHI 4200 eal. - 95 cal. S,.,..M.I r S, exist, wr nre unnble to demnnstrnte this in any simple, ronrlusive mnnnrr. n'c nxy, however. demonstrate the rewtion
9. Black Antimony. This variety is produced spontnneo~~sly from the yellow allotrope by the rapid vonling of antimony vnpor, or by the reaction between oxymn and stihinc nt -40'. I t is chcmicnlly murh more nctive than metnllic antimony. :
