Table 602 

 EFFECTIVE ATOMIC RADII 



491 



Goldschmidt, on the basis of reasonable though empirical assumptions, has calculated effective radii 

 f atoms in various charged conditions; Pauling, on the basis of wave-mechanics, has presented theoretical 

 alues for most of the elements, the two series agreeing well in many cases. The latter values are printed 

 1 bold-faced type; the values considered nontypical are in parentheses; e.g., for silicon we have: Si + ' 

 3.22 — ) 0.39-O.4I. Si° (1.12 — ) 1. 18. Si" 4 (1.98); 2.71, signifying silicon, carrying 4 4- charges, has 

 pparent radius between 0.22 and 0.41; but the lower values relate to compounds where the atoms 

 ppear to be deformed; so Goldschmidt gives 0.39 as most significant. Wave-mechanics yields 0.41. 

 leutral, the radius ranges from 1.12, in abnormal compounds, to 1.18 in those typical; when carrying 



— charges, the value is 1.98, according to calculations deemed faulty, 2.71 according to theory. 



In applying the data to replacements, halides and oxides are usually ionized, and the values in the 

 uter columns apply. Thus in fluorite the value for Ca +2 should be added to that for F" 1 , giving between 

 .32 and 2.42, or 2.37 as a mean; and the observed Ca-F distance in the crystal is 2.36 Angstrom units. 

 a the remaining types of compounds the atoms appear to be largely neutral and the first column should 

 e used. The units are Angstroms. Wherry, Amer. Mineralog., 14, 54, 1929. 



MITHSONIAN TABLES 

 18 



