Electron Configuration

What is the Electron Configuration?

The electron configuration is the summary of where the electrons are located around a nucleus. Each neutral atom has a number of electrons equal to its number of protons. Therefore, these electrons are located in orbitals in an arrangement around the nucleus. The notation indicates that indicates their energy and the type of orbital in which they are located. The types of orbitals and how many electrons each can accommodate is summarized as follows up to the n=4 level.

Level (n) sub-level No. orbitals for each type No. orbitals for each level No max. e– (2n2)
1 s 1 1 2
2 s 1 4 8
p 3
3 s 1 9 18
p 3
d 5
4 s 1 16 32
p 3
d 5
f 7


Then, according to the above table, it needs 2 electrons to fill an orbital s, 6 electrons to fill an orbital p, 10 electrons to fill an orbital d and 14 electrons to fill the orbital f.


However, in order to determine the electron configuration of every element in the periodic table, we will need to know the order of filling of these orbitals.

Order of filling

The order in which the electrons are placed in orbitals is based on the energy of these. Thus gradually filling up by order of this energy according to the Aufbau principle.

The Aufbau principle derived from the Schrödinger equation, which describes the behavior of electrons in an atom.

According to the Aufbau principle, electrons fill the lowest energy orbitals first before occupying higher energy orbitals. This means that in a ground state atom, the electrons will always occupy the orbitals with the lowest energy levels first, and then fill higher energy levels as needed.

The orbitals of lowest energy are filled first, and is determined in the following way:


1s22s22p63s23p64s23d104p65s24d105p66s24145d106p67s25146d107p6 (614 7d10 714) → 8s2

The order of filling of the last three layers are described, has not been able to determine. This is mainly due to non-availability of the necessary amount of the corresponding items to make experimental measurements of physico-chemical properties.

Keep in mind that this order is an estimate, and for certain elements varies as there are configurations that are more stable when the orbitals are filled, semillenos, or empty.

To write the electron configuration, we start with the layer number (n) followed by the type of orbital and finally the superscript indicates how many electrons are in the orbital. For example, an atom of carbon has 6 electrons would be:

Carbon: 1s2 2s2p4

Often abbreviated notation, using the noble gas preceding in order of atomic number in square brackets. For the carbon would be:

Carbon: [He] 2s22p4

The order of filling orbitals follows a specific pattern, which is based on the periodic table. The first two electrons occupy the 1s orbital, followed by two electrons in the 2s orbital. The 2p orbitals are then filled with six electrons, before the 3s orbital is filled with two electrons. This pattern continues until all of the electrons are accounted for.

The Aufbau principle is a useful tool for predicting the electron configurations of atoms and molecules. By following the order of filling orbitals based on the principle, we can determine the electron configuration of an atom or ion, which is essential for understanding its chemical and physical properties.

However, it is important to note that the Aufbau principle is a simplified model that does not account for some exceptions and anomalies that occur in certain elements. For example, the electron configurations of some transition metals and lanthanides are not strictly predictable based on the Aufbau principle alone. Nonetheless, the principle remains a useful starting point for understanding the behavior of electrons in atoms and molecules.

Electron configuration table

The following table shows the electron configuration of the elements, ordered by their atomic number (Z).

3Li[He] 2s1
4Be[He] 2s2
5B[He] 2s2 2p1
6C[He] 2s2 2p2
7N[He] 2s2 2p3
8O[He] 2s2 2p4
9F[He] 2s2 2p5
10Ne[He] 2s2 2p6
11Na[Ne] 3s1
12Mg[Ne] 3s2
13Al[Ne] 3s2 3p1
14Si[Ne] 3s2 3p2
15P[Ne] 3s2 3p3
16S[Ne] 3s2 3p4
17Cl[Ne] 3s2 3p5
18Ar[Ne] 3s2 3p6
19K[Ar] 4s1
20Ca[Ar] 4s2
21Sc[Ar] 3d1 4s2
22Ti[Ar] 3d2 4s2
23V[Ar] 3d3 4s2
24Cr[Ar] 3d5 4s1
25Mn[Ar] 3d5 4s2
26Fe[Ar] 3d6 4s2
27Co[Ar] 3d7 4s2
28Ni[Ar] 3d8 4s2
29Cu[Ar] 3d10 4s1
30Zn[Ar] 3d10 4s2
31Ga[Ar] 3d10 4s2 4p1
32Ge[Ar] 3d10 4s2 4p2
33As[Ar] 3d10 4s2 4p3
34Se[Ar] 3d10 4s2 4p4
35Br[Ar] 3d10 4s2 4p5
36Kr[Ar] 3d10 4s2 4p6
37Rb[Kr] 5s1
38Sr[Kr] 5s2
39Y[Kr] 4d1 5s2
40Zr[Kr] 4d2 5s2
41Nb[Kr] 4d4 5s1
42Mo[Kr] 4d5 5s1
43Tc[Kr] 4d5 5s2
44Ru[Kr] 4d7 5s1
45Rh[Kr] 4d8 5s1
46Pd[Kr] 4d10
47Ag[Kr] 4d10 5s1
48Cd[Kr] 4d10 5s2
49In[Kr] 4d10 5s2 5p1
50Sn[Kr] 4d10 5s2 5p2
51Sb[Kr] 4d10 5s2 5p3
52Te[Kr] 4d10 5s2 5p4
53I[Kr] 4d10 5s2 5p5
54Xe[Kr] 4d10 5s2 5p6
55Cs[Xe] 6s1
56Ba[Xe] 6s2
57La[Xe] 5d1 6s2
58Ce[Xe] 41 5d1 6s2
59Pr[Xe] 43 6s2
60Nd[Xe] 44 6s2
61Pm[Xe] 45 6s2
62Sm[Xe] 46 6s2
63Eu[Xe] 47 6s2
64Gd[Xe] 47 5d1 6s2
65Tb[Xe] 49 6s2
66Dy[Xe] 410 6s2
67Ho[Xe] 411 6s2
68Er[Xe] 412 6s2
69Tm[Xe] 413 6s2
70Yb[Xe] 414 6s2
71Lu[Xe] 414 5d1 6s2
72Hf[Xe] 414 5d2 6s2
73Ta[Xe] 414 5d3 6s2
74W[Xe] 414 5d4 6s2
75Re[Xe] 414 5d5 6s2
76Os[Xe] 414 5d6 6s2
77Ir[Xe] 414 5d7 6s2
78Pt[Xe] 414 5d9 6s1
79Au[Xe] 414 5d10 6s1
80Hg[Xe] 414 5d10 6s2
81Tl[Xe] 414 5d10 6s2 6p1
82Pb[Xe] 414 5d10 6s2 6p2
83Bi[Xe] 414 5d10 6s2 6p3
84Po[Xe] 414 5d10 6s2 6p4
85At[Xe] 414 5d10 6s2 6p5
86Rn[Xe] 414 5d10 6s2 6p6
87Fr[Rn] 7s1
88Ra[Rn] 7s2
89Ac[Rn] 6d1 7s2
90Th[Rn] 6d2 7s2
91Pa[Rn] 52 6d1 7s2
92U[Rn] 53 6d1 7s2
93Np[Rn] 54 6d1 7s2
94Pu[Rn] 56 7s2
95Am[Rn] 57 7s2
96Cm[Rn] 57 6d1 s2
97Bk[Rn] 59 s2
98Cf[Rn] 510 s2
99Es[Rn] 511 s2
100Fm[Rn] 512 s2
101Md[Rn] 513 s2
102No[Rn] 514 s2
103Lr[Rn] 514 7s2 7p1
104Rf[Rn] 514 6d2 7s2
105Db[Rn] 7s2 514 6d3
106Sg[Rn] 7s2 514 6d4
107Bh[Rn] 7s2 514 6d5
108Hs[Rn] 7s2 514 6d6
109Mt[Rn] 7s2 514 6d7
110Ds[Rn] 7s2514 6d8
111Rg[Rn] 5f 14 6d10 7s1
112Cn[Rn] 5f 14 6d10 7s2
113Nh[Rn] 5f 14 6d10 7s2 7p1
114Fl[Rn] 5f 14 6d10 7s2 7p2
115Mc[Rn] 5f 14 6d10 7s2 7p3
116Lv[Rn] 5f 14 6d10 7s2 7p4
117Ts[Rn] 5f 14 6d10 7s2 7p5
118Og[Rn] 5f 14 6d10 7s2 7p6

Electron Configuration Video


Frequently asked questions about electronic configuration

  • What is the electron configuration?

The electron configuration is a description of the electronic structure of an atom. The orbitals are filled with electrons in all shells following three rules: Aufbau’s principle, Pauli’s exclusion principle and Hund’s rule.

  • What is the electron configuration of the chromium atom (Cr Z = 24)?

The expected electron configuration for chromium is 1s2 2s2 2p6 3s2 3p6 3d4 4s2. However, half-filled and fully filled subshell present extra stability, and, thus, the correct electron configuration of crhomium atom [Z = 24] is [Ar] 3d5 4s1.