The diagram is read from left to right, and from top to bottom, as if it were a printed page, to give: Is, 2s,2p, 3s,3p, 4s,3d, 4p, 5s, 4 4 etc. This is the order in which the subshells of atoms are filled. (Pao-Fang Yi gave . .7s, 6d, . .,while the above diagram gives . . . 7s, 5f, 6d, . . . The latter is substantiated empirically by the second rare-earth series of elements-the actinide series -and theoretically by wave mechanics. Hence it is the correct one.) The accompanying figure gives the subshell energy sequence in a form which shows the relationship between the principal and orbital quantum numbers more clearly. Each numbered triangle represents a subshell. The numbers in the triangles give the order in which the various subshells are filled: e. g., 6s is numbered 12-it is the 12th subshell to be filled. I call this number the abbreviated ~ ~ energyd level,, i of the ~ subshell, ~ ~
.
.
.
Letter to the Editor: On page 567 of the November issue of JOuRNAL~ PaO-Fang Yi wrote to you of the order in which the electronic subshells of atoms are filled. He also gave a diagram which illustrates this order. " Ed." In the summer of 1946, I worked out a similar diagram. I t has proved to be very useful in a year of undergraduate general chemistry instruction. I also worked out a mathematical expression that gives the order in which the subshells are filled. The sequence explains Rydberg's atomic number series (for the first time), and why certain (heretofore inexplicable) atomic spectra occur, and it has led to the only periodic table that has amathematical equation to describe it. . . . . The order in which the subshells of atoms are filled has been merely empirical, having been deduced from atomic spectra. However, it can very easily be shown to follow from wave-mechanical theory. Hence it has l a definite theoretical basis. Similarly, Mendeleev's periodic table can be derived from mine-hence from wave mechanics. . . The equation for the subshell energy. sequence is as My subshell energy sequence diagram is so simple follows: that it can be very readily memorized. It then makes + + + - (-1)nC11/8 a very useful mnemonic for working out the structure of E"d. = (n + any atom desired. (Undergraduates find this sort of OLldn-1. thing very interesting. The structures of as-yetREINOW. HAKALA unknown elements can also be worked out!) CHAMPLAIN COLLEGE PLA~BUEG NEW , YOUR This diagram follows: ... f d P a
.
'
'
4 5
...
3 4 5
6
2 3 4 5 6 7
1. 2 3 4 5 6 7 8
.
The dots indicate that the diagram can be extended as far as is desired. The method of its growth is obvious. (Stl'ict numerical order is followed both vertically and horizontally; 1occurs once, 2 twice, 3 three tilhes, etc.; the s column starts with 1, the p column with 2, the d column with 3, the f column with 4, etc.)
To the Editor:
If Johnny investigates the behavior of strongly heated barium carbonate (See November, 1947, p. 568) he will observe that it sizzles when hydrochloric acid is applied no less than it sizzled before heating. The equilibrium pressure of COz in contact with BaO and BaCOsa t 1000°C., avery strong heatingforJohnny, is only 2.7 mm. Hg, 17.7 mm. a t 1100°, 92 rnm. at 1200°, and even at 1300' no more than half an atmosphere, 382 mm. So to prepare BaO Johnny's teacher bas to heat the nitrate not the Sorry he did not know it, F. L. HAHN M E X I C OD , . F., NONOALCO
0
