A. 1. Horvoth 18, Harlow Close Thelwall ~ England Warrington, W A ZHD,
II
Critical Temperature of Elements and the Periodic System
The critical temperature of most nonmetallic elements have been determined experimentally with gwd accuracy. A recent survey of the experimental values is reported by Mathews (1). However, due to the extreme difficulty, only mercury's critical temperature has been measured among the metals. Consequently, a considerable effort has been carried out to predict their critical temperature (2-15). The most extensive investigations have been done by Grosse (16-19). The estimation methods are based on different versions of the relation between the critical t e m ~ e r a t u r eand other physical or thermodynamic properties. However, the most frequently used method is the law of rectilinear diameter. he predicted critical temperatures, using the various versions of methods, provide a considerable discrepancy
between different investigators. I t is not unusual to obtain a deviation from 1000°K (131, (19) to 10,000"K (IS), between two independent methods. In this article the main emphasis is directed onto the similarity-symmetry-analogy principle between the elements allocated in the same group in the periodic system. These elements may he called congeners, and they have closely related physical and chemical properties. Tberefore, it is imperative to relate the critical temperature of all elements to their place in the Mendeleev's classification-the most perfect system of the elements (20)-because the increasing or decreasing character of some properties are typical and relative to the other elements in a group. E.g., the ionization potentials, boiling points, and surface tensions of alkali metals and alkaline earth metals
Figure 1. Critical temperature (OK) of elements.
Volume 50, Number 5, May 1973 / 335
est selected values, the periodic system of elements has been tabulated together with the correlated critical temperatures in Figure 1. The trend of critical temperatures in the different periodic groups is apparent. There are several aspects which arise from the compiled data in Figure 1. 1) The critical temperatures of metals and nonmetals continuously decrease or increase from the first member in each typical group of the periodic system, e.g., decreasing from Li to Fr in the alkali metals group, and increasing from He to Rn in the group of noble gases, etc. 2) The metalloids between the metallic and nonmetallic elements provide a complete transition character in hoth physical and chemical properties. These elements occupy a diagonal region, extending from baron to polonium (B, Si, Ge, As, Sb. Te, and Po) in the periodic table. The elements allocated on the left side (metallic side) of the diagonal line, Al, Ge, Sb, and Po, show the highest critical temperatures in their groups (vertical columns of the periodic table). 3) The correlated critical temperatures of the elements in each group with their molecular weights show linear relationships, see Figure 2. There are no minimum, maximum, or inflection points of curves with the exception of the groups containing metalloid(~).
I
0
5000 10000 Critical Temperature PK)
15000
Figure 2. Critical temperature of elements versus their molecular weights. 1. GroupVlll A. 2.GroupVII A . 3 Group I A.4. GroupVI A. 5. Group I 1 A. 6 . Group of Lanthanides: La-Eu. 7. Group of Lanthanides; Gd-Lu. 8. Group I l l A; 9. Group 01 Actinides: Ac-Am.
The published critical temperature of Ba and Po, 3663°K (2) and 2281°K (2) respective, do not follow the trend of renularity and therefore. the correlated values have been I'ntroduced in Figure 1'. The available critical tem~eraturesfrom the literature ~rovidedsufficient data for the correlation, with the exception of the group of iron (Fe, Ru, and 0s). The effectiveness of the correlation is best illustrated in the group of lanthanides, where the critical temperature of several elements (not available elsewhere) has been predicted. Lilerature Cited (11 Mathem. J.F., Chem Rev.. 72111. 71 119721. (21 Gales, D. S..Thodos.G.,AIChEJournol.6(ll,50(19601. (31 Abrsmous, V. M.. Kirillov. P. L.. Inzh h r . Zh.. Akod. Nouk Bsiorussk SSR.. C ,i . l ),, . IM I I,. (. H. 7 > . .. . ,.
decrease from Na to Fr, and from Be to Ra, respectively, etc. This trend of regularity is very significant and the critical temperatures follow a similar pattern, which is an indication for the relation between ionization potential, boiling point, surface tension, and critical temperature. Fokeev (21) was the only investigator who assigned the critical temperature of elements to the Mendeleev periodical system. Applying the data of Gates and Thodos (21 he concluded that the critical temperature of the elements changed within each period, and increased from the heginning to the middle and then decreased again to the end of each period. However, since Gates and Thodos' investigation (2) more accurate data (9) have been reported, which do not follow Fokeev's observations. Using the lat-
336 /Journal of Chemical Education
(4) Baibuz. V.F.. Tr.Cos. Insf Rikl Khim..(49).113(1952J. (5) Filippou. L. P.. Zh. Fiz. Khim., 3 5 201119631. Sh. Stofri. 245 (19611. (61 Novikou.l.l..Zhidk~eM~tal. (71 Lazarov,V.B..Zh.Fir. Khim.. 3R(91,226bi1964I. 181 MeGonigal. P. J.. Ph.D Thais. Uniu. Microfilms OrdarNo.65-1410,181pp. 191 Dillm,l.G.,Nelwn, P.A.,Swanson, 9. S.J. Cham. Phyr. 44llll,422911966l. 110) Volyak,L.D..Zh.Fiz. Khim.. 40161. 125911966l. (11)Povarnin, P. I.. Tepioobmsn Elem Energ. Usranouok,Nouko. Moscow. LM 11966). (121 Krikorisn.0.H..US. At. EnermComm. UCID-15269, 1966. ltipp. 113) Kopp.1. Z.,Zh Fiz. Khim.. 41(61,147411967l. (I41 Solov'ev.A. N.,hsld T~plplof~z. Svoi~lv. Ve~hcheslu.,216l1961l. (151 Volysk, L. D., Zh. Fir. Khim., 42(2l. 501ll9681. (161 Grosne.A.V..J.lnorg. Nucl Chem., 22.23(1961). (17)Gmsae.A.V..J h a r g Nucl Chem.. 24.147 (1962).
1181 Gms~e.A.V..lnorz. Chrm.. li21.436119621. I& N U C ~ . cYm..27.1171 119651. (20) Van Spronm, J. W.. "The Periodic System of Chemical Elcment~,A History of the First Hundred Yearn." Elsevier. Amsterdam, 1969.36Spp. 121) Fokeev,V.M.,Izo.V w h IJcheb.Zoued.. GeoLRomed, 12l6l145(1969l. 122) Mello., J. W.. (EdilorJ."A Comprehensive Treatise on Inoreanic and Theoretical Chemistry,"Vol.V , Longmans. London. 1924. p. 765.
iw cmase; A. V..J
