Similarly, calculations for actinides give absurd results. Even if calculations are done for d-block elements by taking 1 = 2 the results are ahsurd.
Madelung's Rule Revisited To the Editor:
I wish to comment upon the usefulness of equation (14) of Dr. D. Pan Wong's article "Theoretical Justification of Madelung's Rule" [J. CHEM. EDUC.,56,714 (1979)l.The said equation is where according to author, with the given atomic number ( Z ) , one can easily predict analytically the number of electrons any atom possesses in given 1, the orbital angular momentum quantum number. The example given in the article is Z = 10 and 1 = 3, where N ! ( Z )becomes negative which means atom Z = 10 cannot have f electrons. Thus, this equation would be giving negative values for 1 = 3 u n t o Z = 57. which is certainlv in good aereement with the cokgurationsof elements. Rut if cal&lati&s are done for the lanthanides. the results. as shown by the following table, are misleading.
z
Nl(2) for ! = 3 from eqn. I141
Z 21 30
(3d'.4s2) (3d'0.4s2)
Nl(2) for d = 2 01329 6.4620
However for p- and s-hlock elements, within the approximation stipulated hy the author, the results can be taken to be fair. Z 5 10
3 4
(ls2.2s2p') (1s2.2s2p6) (IsZ,2s') (ls2.2sZ)
NU21 for I= 1 0.6434 = 1.0 5.4892 = 6.0 Nl(2) for I= 0 3.2415 = 3.0 3.7690 = 4.0
Besides this, when the author says "second eqn. (14) may he used to predict which element starts the transition series. For 1 = 2 and NL ( 2 ) = 0 , what would eqn. (14)predict for the value of Z? The answer is Z = 21, Sc. Which element starts the rare earth lanthanides series? 1 = 3 and (6q1/" 7 = 0 gives Z = 57, La." In these calculations it seems that the author has taken N l ( 2 ) = 0 for I = 2 and got Z = 21. But the question is how N l ( 2 ) is zero for 1 = 2 when the element is to start the transition series. We know Sc ( Z = 21) is [Ar] 3d1,4s" hence, if NL(2) is taken to be unity, the value of Z from eqn. (14)comes to be 22.10, which is not correct.
R. C. Sharma P.G. Department of Chemistry Govt. College Kota Kota (Raj.! iNDlA
174
Journal of Chemical Education
