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Atomic Reference Data for Electronic Structure Calculations, 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.

Z Symbol Neutral Positive ion
1 H 1s1 -
2 He 1s2 1s1
3 Li [He] 2s1 1s2
4 Be [He] 2s2 [He] 2s1
5 B [He] 2s2 2p1 [He] 2s2
6 C [He] 2s2 2p2 [He] 2s2 2p1
7 N [He] 2s2 2p3 [He] 2s2 2p2
8 O [He] 2s2 2p4 [He] 2s2 2p3
9 F [He] 2s2 2p5 [He] 2s2 2p4
10 Ne [He] 2s2 2p6 [He] 2s2 2p5
11 Na [Ne] 3s1 [He] 2s2 2p6
12 Mg [Ne] 3s2 [Ne] 3s1
13 Al [Ne] 3s2 3p1 [Ne] 3s2
14 Si [Ne] 3s2 3p2 [Ne] 3s2 3p1
15 P [Ne] 3s2 3p3 [Ne] 3s2 3p2
16 S [Ne]3s2 3p4 [Ne] 3s2 3p3
17 Cl [Ne] 3s2 3p5 [Ne] 3s2 3p4
18 Ar [Ne] 3s2 3p6 [Ne] 3s2 3p5
19 K [Ar] 4s1 [Ne] 3s2 3p6
20 Ca [Ar] 4s2 [Ar] 4s1
21 Sc [Ar] 3d1 4s2 [Ar] 3d1 4s1
22 Ti [Ar] 3d2 4s2 [Ar] 3d2 4s1
23 V [Ar] 3d3 4s2 [Ar] 3d4
24 Cr [Ar] 3d5 4s1 [Ar] 3d5
25 Mn [Ar] 3d5 4s2 [Ar] 3d5 4s1
26 Fe [Ar] 3d6 4s2 [Ar] 3d6 4s1
27 Co [Ar] 3d7 4s2 [Ar] 3d8
28 Ni [Ar] 3d8 4s2 [Ar] 3d9
29 Cu [Ar] 3d10 4s1 [Ar] 3d10
30 Zn [Ar] 3d10 4s2 [Ar] 3d10 4s1
31 Ga [Ar] 3d10 4s2 4p1 [Ar] 3d10 4s2
32 Ge [Ar] 3d10 4s2 4p2 [Ar] 3d10 4s2 4p1
33 As [Ar] 3d10 4s2 4p3 [Ar] 3d10 4s2 4p2
34 Se [Ar] 3d10 4s2 4p4 [Ar] 3d10 4s2 4p3
35 Br [Ar] 3d10 4s2 4p5 [Ar] 3d10 4s2 4p4
36 Kr [Ar] 3d10 4s2 4p6 [Ar] 3d10 4s2 4p5
37 Rb [Kr] 5s1 [Ar] 3d10 4s2 4p6
38 Sr [Kr] 5s2 [Kr] 5s1
39 Y [Kr] 4d1 5s2 [Kr] 5s2
40 Zr [Kr] 4d2 5s2 [Kr] 4d2 5s1
41 Nb [Kr] 4d4 5s1 [Kr] 4d4
42 Mo [Kr] 4d5 5s1 [Kr] 4d5
43 Tc [Kr] 4d5 5s2 [Kr] 4d5 5s1
44 Ru [Kr] 4d7 5s1 [Kr] 4d7
45 Rh [Kr] 4d8 5s1 [Kr] 4d8
46 Pd [Kr] 4d10 [Kr] 4d9
47 Ag [Kr] 4d10 5s1 [Kr] 4d10
48 Cd [Kr] 4d10 5s2 [Kr] 4d10 5s1
49 In [Kr] 4d10 5s2 5p1 [Kr] 4d10 5s2
50 Sn [Kr] 4d10 5s2 5p2 [Kr] 4d10 5s2 5p1
51 Sb [Kr] 4d10 5s2 5p3 [Kr] 4d10 5s2 5p2
52 Te [Kr] 4d10 5s2 5p4 [Kr] 4d10 5s2 5p3
53 I [Kr] 4d10 5s2 5p5 [Kr] 4d10 5s2 5p4
54 Xe [Kr] 4d10 5s2 5p6 [Kr] 4d10 5s2 5p5
55 Cs [Xe] 6s1 [Kr] 4d10 5s2 5p6
56 Ba [Xe] 6s2 [Xe] 6s1
57 La [Xe] 5d1 6s2 [Xe] 5d2
58 Ce [Xe] 4f1 5d1 6s2 [Xe] 4f1 5d2
59 Pr [Xe] 4f3 6s2 [Xe] 4f3 6s1
60 Nd [Xe] 4f4 6s2 [Xe] 4f4 6s1
61 Pm [Xe] 4f5 6s2 [Xe] 4f5 6s1
62 Sm [Xe] 4f6 6s2 [Xe] 4f6 6s1
63 Eu [Xe] 4f7 6s2 [Xe] 4f7 6s1
64 Gd [Xe] 4f7 5d1 6s2 [Xe] 4f7 5d1 6s1
65 Tb [Xe] 4f9 6s2 [Xe] 4f9 6s1
66 Dy [Xe] 4f10 6s2 [Xe] 4f10 6s1
67 Ho [Xe] 4f11 6s2 [Xe] 4f11 6s1
68 Er [Xe] 4f12 6s2 [Xe] 4f12 6s1
69 Tm [Xe] 4f13 6s2 [Xe] 4f13 6s1
70 Yb [Xe] 4f14 6s2 [Xe] 4f14 6s1
71 Lu [Xe] 4f14 5d1 6s2 [Xe] 4f14 6s2
72 Hf [Xe] 4f14 5d2 6s2 [Xe] 4f14 5d1 6s2
73 Ta [Xe] 4f14 5d3 6s2 [Xe] 4f14 5d3 6s1
74 W [Xe] 4f14 5d4 6s2 [Xe] 4f14 5d4 6s1
75 Re [Xe] 4f14 5d5 6s2 [Xe] 4f14 5d5 6s1
76 Os [Xe] 4f14 5d6 6s2 [Xe] 4f14 5d6 6s1
77 Ir [Xe] 4f14 5d7 6s2 [Xe] 4f14 5d7 6s1
78 Pt [Xe] 4f14 5d9 6s1 [Xe] 4f14 5d9
79 Au [Xe] 4f14 5d10 6s1 [Xe] 4f14 5d10
80 Hg [Xe] 4f14 5d10 6s2 [Xe] 4f14 5d10 6s1
81 Tl [Xe] 4f14 5d10 6s2 6p1 [Xe] 4f14 5d10 6s2
82 Pb [Xe] 4f14 5d10 6s2 6p2 [Xe] 4f14 5d10 6s2 6p1
83 Bi [Xe] 4f14 5d10 6s2 6p3 [Xe] 4f14 5d10 6s2 6p2
84 Po [Xe] 4f14 5d10 6s2 6p4 [Xe] 4f14 5d10 6s2 6p3
85 At [Xe] 4f14 5d10 6s2 6p5 [Xe] 4f14 5d10 6s2 6p4
86 Rn [Xe] 4f14 5d10 6s2 6p6 [Xe] 4f14 5d10 6s2 6p5
87 Fr [Rn] 7s1 [Xe] 4f14 5d10 6s2 6p6
88 Ra [Rn] 7s2 [Rn] 7s1
89 Ac [Rn] 6d1 7s2 [Rn] 7s2
90 Th [Rn] 6d2 7s2 [Rn] 6d2 7s1
91 Pa [Rn] 5f2 6d1 7s2 [Rn] 5f2 7s2
92 U [Rn] 5f3 6d1 7s2 [Rn] 5f3 7s2

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  9. Estimate of present authors.
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  11. Estimate of present authors.
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Created October 15, 2015, Updated March 1, 2023