Electron Configuration

Electron Configuration of Elements in Periodic Table

Electron configuration or electronic configuration or electronic structure of atoms or ions of s, p, d, and f block periodic table elements in chemistry is the arrangement or distribution of electrons in different orbitals or energy levels. In learning chemistry or chemical science, the electron holds the key to the chemical world and electronic configuration is useful to find the position of elements in the periodic table. The electronic configuration formula is also used to derive the chemical properties such as oxidizing and reducing, oxidation number, ionization energy, electron affinity, shielding effect, the polarity, acids bases properties, etc.

A reaction to reach chemical equilibrium is the change of electron configuration of reactant and product atoms. Hence the organic and inorganic chemical reactions are better understood by the electronic configuration of atoms of reacting elements.

How to Find Electronic Configuration of Elements?

To find the electron configuration formula first we write the order of electronic energy levels or s, p, d, and f orbitals. For example, the 3s orbital has lower energy than 3p orbitals which again has lower energy than the 3d level.

The modern periodic table classification like s, p, d, and f block elements is based on properties and general electron or electronic configuration of elements.

Electron Energy Levels Diagram

Energy levels are fixed distances where electrons are rotating around the nucleus with definite energy. The energy associated with a certain energy level increases with the increase of its distance from the nucleus.

The hydrogen atom contains only one electron in 1s hydrogen energy levels with electronic configuration 1s¹.

But difficult for readers to remember the electron energy levels diagram for many electronic configurations. Therefore, the trivial way but most convenient way to remember these electronic energy levels is given above the diagram.

• The different electron orbitals originating from the same electronic energy levels are written in horizontal lines.
• Now inclined parallel lines are drawn through the electronic orbitals according to the above picture.
• Filling up the different orbitals by the number of electrons will follow these lines’ configuration.
• According to the above diagram, energy levels ordering where electrons are distributed,
  1s < 2s < 2p < 3s < 3p < 4s < 3d < 4p < 5s < 4d < 5p < 6s < 4f < 5d < 6p < 7s < 5f…

Electrons in Energy Levels

The electronic configuration or arrangement of atoms in different energy levels follows certain rules. The maximum number of electrons in the main energy levels = 2n², where n = principal quantum number.

The maximum number of the electrons in sub-shells like s, p, d, and f orbitals = 2(2l + 1). Where l = 0, 1, 2, 3 for s, p, d, f orbitals. Therefore, s, p, d, and f orbitals contain a maximum of 2, 6, 10, and 14 electrons respectively.

Aufbau Principle

German scientist Aufbau expresses the building-up principle for the electron configuration process in different electronic orbitals of atoms.

According to the Aufbau principle, the electrons are filled up in order of energy. Therefore, the orbitals with the lowest energy filled up first while the highest energy orbital filled up in the end.

Hund’s Rule in Chemistry

According to Hund’s rule in chemistry, electrons are filling in the orbital with maximum spin multiplicity. Hence spin pairing occurs only when vacant orbitals of similar energy are not available for occupation.

The electron will tend to form maximum spin. Electrons with similar spin are configured first.

Electron Configuration and Periodic Table

The electronic configuration formula is very useful to derive some basic properties like the electromagnetic spectrum, chemical bonding, electric polarization, dipole moment, hydrogen bonding, etc.

Modern periodic tables are classified based on chemical behavior and the electronic configuration of elements. Therefore, the electron configuration formula of elements must be connected with the periodic table arrangement.

According to electronic configuration, we classify the periodic table elements into four blocks s, p, d, and f block elements.

Electronic Configuration of s Block Elements

For s block elements, the electron enters the ns orbitals and is progressively filled with atomic number.

Group 1 and group 2 belong to s block elements in the periodic table with general electron configuration ns^1→2. Here n = the number of electronic shells or the number of periods in which the element stays.

Electronic Configuration of Alkali Metals

Group 1 or IA in the periodic table contains seven elements such as hydrogen, lithium, sodium, potassium, rubidium, cesium, and francium.

The general electronic configuration of valence electron = ns¹, where n = 1 to 7. Due to the presence of one electron in the outer electronic structure, they possess very low ionization energy but very high electron affinity.

Atomic number	Symbol	Name	Electronic configuration
1	H	Hydrogen	1s1
3	Li	Lithium	1s2 2s1
11	Na	Sodium	[Ne] 3s1
19	K	Potassium	[Ar] 4s1
37	Rb	Rubidium	[Kr] 5s1
55	Cs	Cesium	[Xe] 6s1
87	Fr	Francium	[Rn] 7s1

Electronic Configuration of Alkaline Earth Metals

The elements of Group 2 or IIA in the periodic table contain beryllium, magnesium, calcium, strontium, barium, and radium. They are also called alkaline earth metals.

The valence shell electronic configuration of group 2 elements or alkaline earth metals = ns². Here n = 1 to 6.

Atomic Number	Symbol	Name	Electronic configuration
4	Be	Beryllium	1s2 2s2
12	Mg	Magnesium	[Ne] 3s2
20	Ca	Calcium	[Ar] 4s2
38	Sr	Strontium	[Kr] 5s2
56	Ba	Barium	[Xe] 6s2
88	Ra	Radium	[Rn] 7s2

Electron Configuration of p Block Elements

The elements in which the p orbital is progressively filled by electrons are called p blocks in the periodic table. Helium whose electronic configuration is 1s² but helium is a member of p block elements.

p block contains six groups from group 13 to group 18. The general electronic configuration formula to find the outer electron configuration of the p block element = ns² np^1→6.

Electronic Configuration of Group 13 Elements

Group 13 or IIIA contains five elements, boron, aluminum, gallium, indium, and thallium. The valence shell electron configuration of group 13 elements = ns² np¹.

Atomic number	Symbol	Name	Electronic configuration
5	B	Boron	1s2 2s2 2p1
13	Al	Aluminum	[Ne] 3s2 3p1
31	Ga	Galium	[Ar] 3d10 4s2 4p1
49	In	Indium	[Kr] 4d10 5s2 5p1
81	Tl	Thallium	[Xe] 4f14 5d10 6s2 6p1
113	Nh	Nihonium	[Rn] 5f14 6d10 7s2 7p1

Electronic Configuration of Group 14 Elements

Carbon, silicon, germanium, tin, and lead in the periodic table belong to group 14 or IVA. The general electron configuration of group 14 elements = ns² np². Where n = 2 to 6.

Atomic number	Symbol	Name	Electronic configuration
6	C	Carbon	1s2 2s2 2p2
14	Si	Silicon	[Ne] 3s2 3p2
32	Ge	Germanium	[Ar] 3d10 4s2 4p2
50	Sn	Tin	[Kr] 4d10 5s2 5p2
82	Pb	Lead	[Xe] 4f14 5d10 6s2 6p2
114	Fl	Flerovium	[Rn] 5f14 6d10 7s2 7p2

Electronic Configuration of Group 15 Elements

The five elements of Group 15 or VA contain nitrogen, phosphorus, arsenic, antimony, and bismuth. The general electron configuration of group 15 elements is written as ns² np³. Here, n = 2 to 6.

Atomic number	Symbol	Name	Electronic configuration
7	N	Nitrogen	1s2 2s2 2p3
15	P	Phosphorus	[Ne] 3s2 3p3
33	As	Arsenic	[Ar] 3d10 4s2 4p3
51	Sb	Antimony	[Kr] 4d10 5s2 5p3
83	Bi	Bismuth	[Xe] 4f14 5d10 6s2 6p3
115	Mc	Moscovium	[Rn] 5f14 6d10 7s2 7p3

Electronic Configuration of Group 16 Elements

Oxygen, sulfur, selenium, tellurium, and polonium in the periodic table belong to group 16 or VIA. The general electron configuration of group 16 elements is ns² np⁴. Here, n = 2 to 6.

Atomic number	Symbol	Name	Electronic configuration
8	O	Oxygen	1s2 2s2 2p4
16	S	Sulfur	[Ne] 3s2 3p4
34	Se	Selenium	[Ar] 3d10 4s2 4p4
52	Te	Tellurium	[Kr] 4d10 5s2 5p4
84	Po	Polonium	[Xe] 4f14 5d10 6s2 6p4
116	Lv	Livermorium	[Rn] 5f14 6d10 7s2 7p4

Electronic Configuration of Halogens

Fluorine, chlorine, bromine, iodine, and astatine in the periodic table belong to group 17 or the halogens family. The general electron configuration of group 17 elements is ns² np⁵. Here, n = 2 to 6.

Atomic number	Symbol	Name	Electronic configuration
9	F	Fluorine	1s2 2s2 2p5
17	Cl	Chlorine	[Ne] 3s2 3p5
35	Br	Bromine	[Ar] 3d10 4s2 4p5
53	I	Iodine	[Kr] 4d10 5s2 5p5
85	As	Astatine	[Xe] 4f14 5d10 6s2 6p5
117	Ts	Tennessine	[Rn] 5f14 6d10 7s2 7p5

Electronic Configuration of Noble Gases

Neon, argon, krypton, xenon, and radon in the periodic table belong to group 18 or noble gases. The general electron configuration of noble gases or group 18 elements is ns² np⁶. Here, n = 1 to 6.

Atomic Number	Symbol	Name	Electronic configuration
2	He	Helium	1s2
10	Ne	Neon	[He] 2s2 2p6
18	Ar	Argon	[Ne] 3s2 3p6
36	Kr	Krypton	[Ar] 3d10 4s2 4p6
54	Xe	Xenon	[Kr] 4d10 5s2 5p6
86	Rn	Radon	[Xe] 4f14 5d10 6s2 6p6
118	Os	Oganesson	[Rn] 5f14 6d10 7s2 7p6

Electronic Configuration of d Block Elements

The elements in which the electron enters (n−1)d orbital are called d block elements. These are placed in the middle of the periodic table, between s and p block elements due to their chemical behavior like boiling point, melting by specific heat, density, ionization energy, bonding, etc.

The general electronic configuration of valence electrons of 3d, 4d, 5d, and 6d elements = ns^0,1,2 (n−1)d^1→10.

These elements are called transition metals or elements. The names, symbols, and valence shell electronic configuration of all the d block elements or transition metals are:

3d Block Elements Electronic Configuration

The first crystalline solid metal in the 3d series or first transition series starts with scandium and ends with zinc. Hence, when the twenty-first electron goes to the next available higher energy 3d orbital, the five 3d subshells fill with ten electrons.

The general electronic configuration of valence electrons of 3d series or first transition series like scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, and zinc = [Ar] 4S^1→2 3d^1→10.

Atomic number	Symbol	Name	Electronic configuration
21	Sc	Scandium	[Ar] 4s2 3d1
22	Ti	Titanium	[Ar] 4s2 3d2
23	V	Vanadium	[Ar] 4s2 3d3
24	Cr	Chromium	[Ar] 4s1 3d5
25	Mn	Manganese	[Ar] 4s2 3d5
26	Fe	Iron	[Ar] 4s2 3d6
27	Co	Cobalt	[Ar] 4s2 3d7
28	Ni	Nickel	[Ar] 4s2 3d8
29	Cu	Copper	[Ar] 4s1 3d10
30	Zn	Zinc	[Ar] 4s1 3d10

4d Block Elements

Atomic number	Symbol	Name	Electronic configuration
39	Y	Yttrium	[Kr] 4d1 5s2
40	Zr	Zirconium	[Kr] 4d2 5s2
41	Nb	Niobium	[Kr] 4d3 5s2
42	Mo	Molybdenum	[Kr] 4d5 5s1
43	Tc	Technetium	[Kr] 4d5 5s2
44	Ru	Ruthenium	[Kr] 4d7 5s1
45	Rh	Rhodium	[Kr] 4d8 5s1
46	Pd	Palladium	[Kr] 4d10 5s0
47	Ag	Silver	[Kr] 4d10 5s1
48	Cd	Cadmium	[Kr] 4d10 5s2

5d Block Elements

Atomic number	Symbol	Name	Electronic configuration
57	La	Lanthanum	[Xe] 5d1 6s2
72	Hf	Hafnium	[Xe] 4f14 5d2 6s2
73	Ta	Tantalum	[Xe] 4f14 5d3 6s2
74	W	Tungsten	[Xe] 4f14 5d4 6s2
75	Re	Rhenium	[Xe] 4f14 5d5 6s2
76	Os	Osmium	[Xe] 4f14 5d6 6s2
77	Ir	Iridium	[Xe] 4f14 5d7 6s2
78	Pt	Platinum	[Xe] 4f14 5d9 6s1
79	Au	Gold	[Xe] 4f14 5d10 6s1
80	Hg	Mercury	[Xe] 4f14 5d10 6s2

6d Block Elements

Atomic number	Symbol	Name	Electronic configuration
89	Ac	Actinium	[Rn] 6d1 7s2
104	Rf	Rutherfordium	[Rn] 5f14 6d2 7s2
105	Db	Dubnium	[Rn] 5f14 6d3 7s2
106	Sg	Seaborgium	[Rn] 5f14 6d4 7s2
107	Bh	Bohrium	[Rn] 5f14 6d5 7s2
108	Hs	Hassium	[Rn] 5f14 6d6 7s2
109	Mt	Meitnerium	[Rn] 5f14 6d7 7s2
110	Ds	Darmstadtium	[Rn] 5f14 6d9 7s1
111	Rg	Roentgenium	[Rn] 5f14 6d10 7s1
112	Cn	Copernicium	[Rn] 5f14 6d10 7s2

Electron Configuration Exceptions

Chromium, and copper, the 3d elements of our environment reveal their general form of electron configuration trends in the periodic table. The general electronic configuration of chromium and copper is [Ar]4s² 3d⁴ and [Ar]4s² 3d⁹.

In the periodic table elements, the half-filled and filled orbital’s electron configuration formula is relatively more stable than the partially filled orbitals. Therefore, the 3d orbital of chromium and copper rearranges to form new electronic configurations to gain extra chemical stability by exchange energy. These electronic configurations are represented as [Ar]4s¹ 3d⁵ and [Ar] 4s¹ 3d¹⁰.

Electron Configuration of f Block Elements

4f Block Elements

Atomic number	Symbol	Name	Electronic configuration
58	Ce	Cerium	[Xe] 4f15d16s2
59	Pr	Praseodymium	[Xe] 4f36s2
60	Nd	Neodymium	[Xe] 4f46s2
61	Pm	Promethium	[Xe] 4f56s2
62	Sm	Samarium	[Xe]4f66s2
63	Eu	Europium	[Xe] 4f76s2
64	Gd	Gadolinium	[Xe] 4f75d16s2
65	Tb	Terbium	[Xe] 4f96s2
66	Dy	Dysprosium	[Xe] 4f106s2
67	Ho	Holmium	[Xe] 4f116s2
68	Er	Erbium	[Xe] 4f126s2
69	Tm	Thulium	[Xe]4f136s2
70	Yb	Ytterbium	[Xe] 4f146s2
71	Lu	Lutetium	[Xe] 4f145d16s2

5f Block Elements

Atomic number	Symbol	Name	Electronic configuration
90	Th	Thorium	[Rn] 6d27s2
91	Pa	Protactinium	[Rn] 5f26d17s2
92	U	Uranium	[Rn] 5f36d17s2
93	Np	Neptunium	[Rn] 5f46d17s2
94	Pu	Plutonium	[Rn] 5f67s2
95	Am	Americium	[Rn] 5f77s2
96	Cm	Curium	[Rn] 5f76d17s2
97	Bk	Berkelium	[Rn] 5f97s2
98	Cf	Californium	[Rn] 5f107s2
99	Es	Einsteinium	[Rn] 5f117s2
100	Fm	Fermium	[Rn] 5f127s2
101	Md	Mendelevium	[Rn] 5f137s2
102	No	Nobelium	[Rn] 5f147s2
103	Lw	Lawrencium	[Rn] 5f147s27p1