Electronic configurations of the elements

The ground electronic configurations of the neutral elements used here are obtained from the most recent compilation [1] produced by the NIST Atomic Physics Division. Some of these differ from those found in older references. The ground electronic configurations of first cations are in most cases obtained from a previous compilation [2] . There are several cases for which that work gives no identification of configuration, and for these we have used identifications made in the scientific literature. The cases concerned are Ta+ [3], W+ [4], Re+ [5], Os+ [6], Ir+ [7], Po+ [8], At+ [9], Rn+ [10], Fr+ [11], Pa+ [12], and U+ [12].

The ground electronic configurations of the elements H through U and their first cations are given below. The notation [X] indicates that all subshells associated with the noble gas X are fully occupied.

                      Electronic Configuration
 Z    Symbol     Neutral                    Positive ion

 1      H       1s^1                           -
 2      He      1s^2                        1s^1
 3      Li      [He] 2s^1                   1s^2
 4      Be      [He] 2s^2                   [He] 2s^1
 5      B       [He] 2s^2 2p^1              [He] 2s^2 
 6      C       [He] 2s^2 2p^2              [He] 2s^2 2p^1
 7      N       [He] 2s^2 2p^3              [He] 2s^2 2p^2
 8      O       [He] 2s^2 2p^4              [He] 2s^2 2p^3
 9      F       [He] 2s^2 2p^5              [He] 2s^2 2p^4
10      Ne      [He] 2s^2 2p^6              [He] 2s^2 2p^5
11      Na      [Ne] 3s^1                   [He] 2s^2 2p^6
12      Mg      [Ne] 3s^2                   [Ne] 3s^1
13      Al      [Ne] 3s^2 3p^1              [Ne] 3s^2 
14      Si      [Ne] 3s^2 3p^2              [Ne] 3s^2 3p^1
15      P       [Ne] 3s^2 3p^3              [Ne] 3s^2 3p^2
16      S       [Ne] 3s^2 3p^4              [Ne] 3s^2 3p^3
17      Cl      [Ne] 3s^2 3p^5              [Ne] 3s^2 3p^4
18      Ar      [Ne] 3s^2 3p^6              [Ne] 3s^2 3p^5
19      K       [Ar] 4s^1                   [Ne] 3s^2 3p^6
20      Ca      [Ar] 4s^2                   [Ar] 4s^1
21      Sc      [Ar] 3d^1 4s^2              [Ar] 3d^1 4s^1 
22      Ti      [Ar] 3d^2 4s^2              [Ar] 3d^2 4s^1 
23      V       [Ar] 3d^3 4s^2              [Ar] 3d^4  
24      Cr      [Ar] 3d^5 4s^1              [Ar] 3d^5  
25      Mn      [Ar] 3d^5 4s^2              [Ar] 3d^5 4s^1 
26      Fe      [Ar] 3d^6 4s^2              [Ar] 3d^6 4s^1 
27      Co      [Ar] 3d^7 4s^2              [Ar] 3d^8 
28      Ni      [Ar] 3d^8 4s^2              [Ar] 3d^9 
29      Cu      [Ar] 3d^10 4s^1             [Ar] 3d^10  
30      Zn      [Ar] 3d^10 4s^2             [Ar] 3d^10 4s^1 
31      Ga      [Ar] 3d^10 4s^2 4p^1        [Ar] 3d^10 4s^2  
32      Ge      [Ar] 3d^10 4s^2 4p^2        [Ar] 3d^10 4s^2 4p^1 
33      As      [Ar] 3d^10 4s^2 4p^3        [Ar] 3d^10 4s^2 4p^2
34      Se      [Ar] 3d^10 4s^2 4p^4        [Ar] 3d^10 4s^2 4p^3
35      Br      [Ar] 3d^10 4s^2 4p^5        [Ar] 3d^10 4s^2 4p^4
36      Kr      [Ar] 3d^10 4s^2 4p^6        [Ar] 3d^10 4s^2 4p^5
37      Rb      [Kr] 5s^1                   [Ar] 3d^10 4s^2 4p^6
38      Sr      [Kr] 5s^2                   [Kr] 5s^1
39      Y       [Kr] 4d^1 5s^2              [Kr] 5s^2 
40      Zr      [Kr] 4d^2 5s^2              [Kr] 4d^2 5s^1 
41      Nb      [Kr] 4d^4 5s^1              [Kr] 4d^4  
42      Mo      [Kr] 4d^5 5s^1              [Kr] 4d^5 
43      Tc      [Kr] 4d^5 5s^2              [Kr] 4d^5 5s^1 
44      Ru      [Kr] 4d^7 5s^1              [Kr] 4d^7 
45      Rh      [Kr] 4d^8 5s^1              [Kr] 4d^8 
46      Pd      [Kr] 4d^10                  [Kr] 4d^9
47      Ag      [Kr] 4d^10 5s^1             [Kr] 4d^10 
48      Cd      [Kr] 4d^10 5s^2             [Kr] 4d^10 5s^1 
49      In      [Kr] 4d^10 5s^2 5p^1        [Kr] 4d^10 5s^2  
50      Sn      [Kr] 4d^10 5s^2 5p^2        [Kr] 4d^10 5s^2 5p^1 
51      Sb      [Kr] 4d^10 5s^2 5p^3        [Kr] 4d^10 5s^2 5p^2
52      Te      [Kr] 4d^10 5s^2 5p^4        [Kr] 4d^10 5s^2 5p^3
53      I       [Kr] 4d^10 5s^2 5p^5        [Kr] 4d^10 5s^2 5p^4
54      Xe      [Kr] 4d^10 5s^2 5p^6        [Kr] 4d^10 5s^2 5p^5
55      Cs      [Xe] 6s^1                   [Kr] 4d^10 5s^2 5p^6
56      Ba      [Xe] 6s^2                   [Xe] 6s^1
57      La      [Xe] 5d^1 6s^2              [Xe] 5d^2 
58      Ce      [Xe] 4f^1 5d^1 6s^2         [Xe] 4f^1 5d^2
59      Pr      [Xe] 4f^3 6s^2              [Xe] 4f^3 6s^1 
60      Nd      [Xe] 4f^4 6s^2              [Xe] 4f^4 6s^1 
61      Pm      [Xe] 4f^5 6s^2              [Xe] 4f^5 6s^1 
62      Sm      [Xe] 4f^6 6s^2              [Xe] 4f^6 6s^1 
63      Eu      [Xe] 4f^7 6s^2              [Xe] 4f^7 6s^1 
64      Gd      [Xe] 4f^7 5d^1 6s^2         [Xe] 4f^7 5d^1 6s^1 
65      Tb      [Xe] 4f^9 6s^2              [Xe] 4f^9 6s^1
66      Dy      [Xe] 4f^10 6s^2             [Xe] 4f^10 6s^1 
67      Ho      [Xe] 4f^11 6s^2             [Xe] 4f^11 6s^1
68      Er      [Xe] 4f^12 6s^2             [Xe] 4f^12 6s^1
69      Tm      [Xe] 4f^13 6s^2             [Xe] 4f^13 6s^1
70      Yb      [Xe] 4f^14 6s^2             [Xe] 4f^14 6s^1
71      Lu      [Xe] 4f^14 5d^1 6s^2        [Xe] 4f^14 6s^2
72      Hf      [Xe] 4f^14 5d^2 6s^2        [Xe] 4f^14 5d^1 6s^2
73      Ta      [Xe] 4f^14 5d^3 6s^2        [Xe] 4f^14 5d^3 6s^1
74      W       [Xe] 4f^14 5d^4 6s^2        [Xe] 4f^14 5d^4 6s^1
75      Re      [Xe] 4f^14 5d^5 6s^2        [Xe] 4f^14 5d^5 6s^1
76      Os      [Xe] 4f^14 5d^6 6s^2        [Xe] 4f^14 5d^6 6s^1
77      Ir      [Xe] 4f^14 5d^7 6s^2        [Xe] 4f^14 5d^7 6s^1
78      Pt      [Xe] 4f^14 5d^9 6s^1        [Xe] 4f^14 5d^9 
79      Au      [Xe] 4f^14 5d^10 6s^1       [Xe] 4f^14 5d^10 
80      Hg      [Xe] 4f^14 5d^10 6s^2       [Xe] 4f^14 5d^10 6s^1
81      Tl      [Xe] 4f^14 5d^10 6s^2 6p^1  [Xe] 4f^14 5d^10 6s^2 
82      Pb      [Xe] 4f^14 5d^10 6s^2 6p^2  [Xe] 4f^14 5d^10 6s^2 6p^1
83      Bi      [Xe] 4f^14 5d^10 6s^2 6p^3  [Xe] 4f^14 5d^10 6s^2 6p^2
84      Po      [Xe] 4f^14 5d^10 6s^2 6p^4  [Xe] 4f^14 5d^10 6s^2 6p^3
85      At      [Xe] 4f^14 5d^10 6s^2 6p^5  [Xe] 4f^14 5d^10 6s^2 6p^4
86      Rn      [Xe] 4f^14 5d^10 6s^2 6p^6  [Xe] 4f^14 5d^10 6s^2 6p^5
87      Fr      [Rn] 7s^1                   [Xe] 4f^14 5d^10 6s^2 6p^6
88      Ra      [Rn] 7s^2                   [Rn] 7s^1
89      Ac      [Rn] 6d^1 7s^2              [Rn] 7s^2
90      Th      [Rn] 6d^2 7s^2              [Rn] 6d^2 7s^1
91      Pa      [Rn] 5f^2 6d^1 7s^2         [Rn] 5f^2 7s^2
92      U       [Rn] 5f^3 6d^1 7s^2         [Rn] 5f^3 7s^2

Sources:

W. C. Martin and W. L. Wiese, "Atomic Spectroscopy," in Atomic, Molecular, and Optical Physics Handbook, ed. G. W. F. Drake, American Institute of Physics (Woodbury NY 1996)
C. E. Moore, Ionization Potentials and Ionization Limits Derived from the Analyses of Optical Spectra, Nat.Stand.Ref.Data Ser., Nat. Bur. Stand.(U.S.), 34 (1970)
J. Wyart, Opt. Pura Apl. (Spain) 10, 177 (1977); C. Kiess, J. Res. Nat. Bur. Standards 66A, 111 (1962)
D. D. Lann, J. Res. Nat. Bur. Standards 68A, 207 (1964)
W. F. Meggers, J. Res. Nat. Bur. Standards 61, 441 (1958)
Th. A. M. van Kleef and P. F. A. Klinkenberg, Physica 27, 83 (1961)
Th. A. M. van Kleef and B. C. Matsh, Physica 95C, 251 (1978)
G. W. Charles, J. Opt. Soc. Am. 56, 1292 (1966)
Estimate of present authors
C. Moore Atomic Energy Levels, NBS 35 3 (1971)
Estimate of present authors
J. Blaise and J.-F. Wyart Energy levels and atomic spectra of actinides, International Tables of Selected Constants 20, Tables de Constantes (Paris, France 1992)

Electronic configurations of the elements

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