Electron configuration of elements

The electron configuration of periodic elements

Electron configuration holds the key to the chemical world. Our present-day understanding of the chemical properties of inorganic and organic compounds based on the electronic configuration of the constituent elements.

Thus the chemical bonding in a reaction is the arrangement of electrons of reactant atoms. Periodic classification also based on the electron configuration of the elements.

In multi-electron atoms, experimental studies of atomic spectra show that orbitals with the same value of principal quantum numbers have different values of azimuthal quantum numbers. Thus these quantum levels are different energy values.

3S orbital lower energy than 3P orbitals which again lower energy than 3d orbitals. But the orbitals belonging to a particular type ( P or d or f ) will be of the equal energy of an atom or an ion.

Rules for writing electronic configuration

The electron configuration of elements or its ions takes place according to the following rules

  1. The maximum number of electrons in the main quantum shell = 2n2. Where n = principal quantum number.
  2. Again we see that the principal quantum shell divided into sub shell s, p, d, f and the maximum capacity of electrons in a subshell = 2(2l +1).
    Where l = 0, 1, 2, 3 for s, p, d, f orbitals respectively.
  3. Aufbau building up principle provides the electron filling up process. Hence according to this principle, the orbitals are filled up in the order of increasing energy of an electron. Thus orbitals with the lowest energy filled up first while the highest energy orbital filled up in the end.
  4. Electrons will tend to maintain maximum spin. Thus electrons with similar spin occupied first will prefer to remain unpaired.
  5. According to Hund’s rule, electrons are filling in the orbital with maximum spin multiplicity.
  6. Spin pairing occurs only when vacant orbitals of similar energy are not available for occupation.

Electron configuration and energy levels

It is difficult for the readers to remember the orbital energy diagram for many-electrons atoms. Thus a trivial way to remember these energy levels provides below this diagram

Electron shells and electronic configuration
Electron shells
  1. The different orbitals originating from the same principal quantum number n are written in the horizontal lines.
  2. Now inclined parallel lines are drawn through the orbitals according to the above picture. Filling up the different orbitals by electrons will follow these lines.

According to this diagram, the energy levels are
1S < 2S < 2P < 3S < 3P < 4S < 3d < 4P < 5S < 4d < 5P < 6S < 4f < 5d < 6P < 7S < 5f…

Pauli exclusion principle

Pauli exclusion principle uses for the pictorial representation of electron configuration.

No two electrons of the atom can have the same four quantum numbers.

An alternative statement of Pauli’s exclusion principle, no more than two electrons can be placed in one and the same orbital.

When an orbital contains two electrons, the electrons are paired. These two electrons per orbital given the maximum accommodation of electrons.

Periodic table and electronic configuration

Extranuclear electrons are responsible for the chemical behavior of elements and periodic classification of the elements also based on the chemical behavior.

Thus the electronic configuration of elements must be connected with the periodic table. Especially, the arrangement of the electrons in the outermost orbitals detects the position of the elements in the periodic table.

S block electron configuration

Group 1 and 2 belong to S-block elements in the periodic table with one or two-electron or electrons in outermost s orbital. Thus the general electron configuration

nS1→2

Electronic structure of group 1 elements

Atomic
Number
Elements Electron Configuration
1 Hydrogen (H) 1S1
3 Lithium (Li) 1S2 2S1
11 Sodium (Na) [Ne] 3S1
19 Potassium (K) [Ar] 4S1
37 Rubidium (Rb) [Kr] 5S1
55 Cesium (Cs) [Xe] 3S1
87 Francium (Fr) [Rn] 3S1

Electronic structure of group 2 elements

Atomic
Number
Elements Electron Configuration
2 Helium (He) 1S2
4 Beryllium (Be) 1S2 2S2
12 Magnesium(Mg) [Ne] 3S2
20 Calcium (K) [Ar] 4S2
38 Strontium (Sr) [Kr] 5S2
56 Barium (Ba) [Xe] 6S2
88 Radium (Ra) [Rn] 7S2

Electronic configuration of the P block

P block constructed by six groups from the group-13 to group-18 and from period 2 to period 6 with valence shell configuration nP1 to nP6 in the periodic table. Thus the general outer electronic configuration of the p-block element is

nS2 nP1→6

Electronic configuration of group 13 elements

Atomic
Number
Elements Electron Configuration
5 Boron (B) 1S22S22P1
13 Aluminum (Al) [Ne] 3S23P1
31 Galium (Ga) [Ar] 4S24P1
49 Indium (In) [Kr] 5S25P1
81 Thallium (Tl) [Xe] 6S26P1

Electronic configuration of group 14 elements

Atomic
Number
Elements Electron Configuration
6 Carbon (C) 1S22S22P2
14 Silicon (Si) [Ne] 3S23P2
32 Germanium (Ge) [Ar] 4S24P2
50 Tin (Sn) [Kr] 5S25P2
82 Lead (Pb) [Xe] 6S26P2

Electronic configuration of group 15 elements

Atomic
Number
Elements Electron Configuration
7 Nitrogen (N) 1S22S22P3
15 Phosphorus (P) [Ne] 3S23P3
33 Arsenic (Ge) [Ar] 4S24P3
51 Antimony (Sn) [Kr] 5S25P3
83 Bismuth (Pb) [Xe] 6S26P3

Electronic configuration of group 16 elements

Atomic
Number
Elements Electron Configuration
8 Oxygen (O) 1S22S22P4
16 Sulfur (S) [Ne] 3S23P4
34 Selenium (Se) [Ar] 4S24P4
52 Tellurium (Te) [Kr] 5S25P4
84 Polonium (Po) [Xe] 6S26P4

Electronic configuration of group 17 elements

Atomic
Number
Elements Electron Configuration
9 Fluorine (F) 1S22S22P5
17 Chlorine (Cl) [Ne] 3S23P5
35 Bromine (Br) [Ar] 4S24P5
53 Iodine (I) [Kr] 5S25P5
85 Austin (At) [Xe] 6S26P5

Electronic configuration of noble gases

Atomic
Number
Elements Electron Configuration
10 Neon (Ne) 1S22S22P6
18 Argon (Ar) [Ne] 3S23P6
36 Krypton (Kr) [Ar] 4S24P6
54 Xenon (Xe) [Kr] 5S25P6
86 Radon (Rn) [Xe] 6S26P6

d-block electron configuration

The first metal in the first transition series starts with scandium and ending with zinc.

Thus the twenty-first electron goes to the next available higher energy 3d orbital and five 3d subshells with the capacity of ten electrons. So the general electron configuration of 3d block elements are

[Ar] 4S1→2 3d1→10

Electronic configuration of 3d series

Elements Electron Configuration
Scandium (Sc) [Ar] 4S2 3d1
Titanium (Ti) [Ar] 4S2 3d2
Vanadium (V) [Ar] 4S2 3d3
Chromium (Cr) [Ar] 4S1 3d5
Manganese (Mn) [Ar] 4S2 3d5
Iron (Fe) [Ar] 4S2 3d6
Cobalt (Co) [Ar] 4S2 3d7
Nickel (Ni) [Kr] 4S2 3d8
Copper (Cu) [Ar] 4S1 3d10
Zinc (Zn) [Ar] 4S2 3d10

Experimental studies on Cr and Cu revel their general electron configuration trends. The general electron configuration of Cr and Cu are

Cr [Ar] 4S2 3d4
Cu [Ar] 4S2 3d9

But half-filled or filled orbital is relatively more stable than the partially filled orbital. Thus Cr and Cu reordering its electrons. to gain extra stability associated with a half-filled or filled d subshell.