4 88 



Table 601 

 ELECTRON CONFIGURATIONS IN NORMAL ATOM 



— for s electrons, 2, 

 electrons, etc. 



3, 4 — for p 



Individual electrons in an atom may be designated by two quantum numbers, "azi- 

 muthal" and "total". The first is expressed by s, p, d, etc.; the last numerically in specific 

 cases, by n in general. 



Designation of quantum numbers: 

 Azimuth quantum: literal, s; number, o; Bohr, k, 1 ; The total quantum number is equal to 



p 1 2 or greater than l + 1, i.e., 1, 2, 3, 



d 2 3 



f 3 4 



g 4 5 



h etc. 5 6 



An electron is called, e.g., a 6p electron, 6 for the total quantum number, p implying an l 

 value of 1. Note that 4p, 5s, 3d, etc., electrons are equivalent to Bohr's 42, 51, 33 electrons. 

 The number of electrons for a given type in an atom may be expressed by an exponent, 

 e.g., 3d 5 . For more detailed connection between configurations and spectroscopic terms see 

 Hund's book. The lower-case letters n, 1, s, j, m should be used for the quantum numbers 

 of an electron, and the capitals L, S, J, M for the quantum numbers of a term (or level) of 

 an atom, ionized or neutral. A specification of atomic structure would include all the inner 

 electrons, e.g., for Fe in its normal state is 2 2s 2 2p 6 3s 2 3p 6 3d 6 4s 2 . For short only those electrons 

 "outside" an inert gas shell need be considered. A complete np 6 group, and all the groups 

 which are normally completed earlier in the periodic table, can be neglected. Thus the 

 notation for the normal state of Fe becomes 3d 6 4s 2 . 



Examples of the notation for a level and the configuration from which it arises is 3d 6 4s 2 

 5 D 4 ,the normal state of the iron atom; 2s 2 2p 3 4 S°i i /2 , the low level of O II. The total quantum 

 numbers may be omitted when they are the lowest which the particular sort of electron 

 can have if not belonging to already completed shells. For example, 4s, 4p, 3d, 4f in spectra 

 from K I to Zn I and Ca II to Ga II, etc., are the s, p, d, and f electrons of lowest quantum 

 numbers not belonging to completed groups. The 3p 6 group is completed and the 3s 2 and all 

 the groups of smaller n have been previously completed, leaving 4s, 4p, 3d, 4f still to be 

 added. These last can therefore be represented by s, p, d and f. 



The normal state of Fe I would thus be designated as d 6 s 2 5 D4, that of II ass 2 p 3 4 S°i i /2 . 

 For Ge I, in which the electron groups 3d 10 and 4s 2 may be regarded as completed, the elec- 

 trons to be represented by the letters alone would be the 5s, 4p, 4d, and 4f electrons; and so on. 

 Odd terms arise when the sum of the 1 values for all electrons is odd, even terms from con- 

 figurations for which the 1 sum is even. Since the 1 sum for completed groups is always even, 

 only outer uncompleted groups need be considered. Even (odd) terms are those in which the 

 number of p and f electrons together is even (odd). In the parts of the periodic table where 

 s and d groups are being completed the lowest terms of all the atoms are even. Where p 

 groups are being completed (and also in the rare earth f-group) the lowest terms are alter- 

 nately odd and even. Except in the rare earth group the only spectra for which the normal 

 state corresponds to an odd term are B I, N I, F I and C II, O II, Ne II etc. and the homo- 

 logous spectra in later periods. 



Permitted transitions are those in which the 1 of one electron changes by one unit, (and 

 the 1 of another electron by o or 2 units, if two electrons change) so that all such transitions 

 are between even and odd terms. 



Electron Configurations 1 



Ele- 

 ment 



H 

 He 



Li 

 Be 

 B 

 C 



N 







F 



Ne 



Na 



Mg 



Al 



Si 



P 



S 



CI 



A 



M 



3.0 3.1 3.2 



3s 3P 3d 



4.0 4.1 4.2 4.3 



4s 4p 4d 4f 



5.0 5.1 5.2 



5S 5P Sd 



Same as for neon 



1 Based by permission upon table by Ruark and Urey. Atoms, molecules, and quanta, 1930. 

 Smithsonian Tables 



