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Electron Configuration

Humans by nature tend to be systematic and that is achieved by proper arrangement. Humans have tried to arrange the elements too. Efforts were made by various chemists, and Mendeleev was one of them. He arranged the elements by atomic weight.

Electronic configuration is the arrangement of electrons in an atom in different shells and sub-shells. After the discovery of the shells and sub-shells, various physical and chemical properties of the elements were linked to the electronic configuration. As a result, attempts were made to arrange elements by their electronic configuration, so that their properties would obviously fall in a trend. Subsequently, the modern arrangement is evolved wherein elements are organized by atomic number. This is known as the modern periodic table.

The modern periodic table has elements arranged according to their electronic configurations. From left to right, i.e., in a period, the arrangement is such that each subsequent electron is added to the same shell. There are certain steps for writing the electronic configuration.

Step-1 

Find out the atomic number of the element from periodic table. Since, in an atom, the number of protons which is the atomic number is equal to the number of electrons, the atomic number will give you the information about the number of electrons in that atom . Let's take the example of calcium. The atomic number of calcium is 20.

Step-2

Follow the electron configuration chart. 

Electron Configuration Chart

Now, fill electrons by following the arrows of the electron configuration chart. Remember that the s-orbital can accommodate a maximum of two electrons while the p-orbital sets can hold six electrons in three orbitals. In the same way d-orbital set contains ten and f-orbital sets contain fourteen electrons in five and seven orbitals respectively.

Step-3

After filling given electrons in the energy levels, write the electronic configuration in the given manner.

[X] [Y] [Z]

Where, X represents the energy level, Y is for the sub-shell which is named as s, p, d and f. The number of sub-shells increases with the energy level. The number Z is the number of electrons present in a sub-shell.

We can represent electron configuration chart by using principle quantum number notifications also.

Quantum Number

For filling given electrons, we have to start form the K shell and move to higher levels.

 

Electronic Configuration in the Period

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Example

Configuration of Li atomic number. 3, is 1s2 , 2s1

Configuration of Be atomic no. 4, is 1s2 , 2s2

Configuration of B atomic no. 5, is 1s2 , 2s2, 2p1

Configuration of C atomic no. 6, is 1s2 , 2s2 , 2p2

and so on till Neon,the last element.

This addition of each subsequent electron results in a completely new configuration and as a result the chemical properties of the subsequent element changes gradually. At the end of each row, a drastic shift occurs in the chemical properties.

Use the below widget to find the electron configuration.

Electronic Configuration in the Group

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From top to bottom in a column, i.e., in a group, each subsequent electron is added to the new shell, but in the same sub-shell, e.g., in the 1st group,

Configuration of H atomic number.1,is 1s1

Configuration of Li atomic no. 3, is 1s2 ,2s1

Configuration of Na atomic no. 11, is 1s2 ,s2,2p6 ,3s1

Configuration of K atomic no. 19, is 1s2 ,2s2 ,2p6,3s2 ,3p6,4s1

and so on till Neon, the last element.

The number of valence shell electrons in an atom would determine the way it will interact with other atoms and therefore determines its chemical properties.

Thus the outermost configuration, which is responsible for various properties such as valency, oxidation states, etc., remains same. Hence in a group, the physical and chemical properties are same. To illustrate, the halogens are strong electronegative elements.


Valence Electron Configuration

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The electrons present in the outer most shell of an atom which takes part in chemical reactions, are known as valence electrons.
These electrons can combine with valence electrons of other atoms to form chemical bonds. Hence valence electrons affect the chemical properties and bonding nature of an atom.

The electronic configuration of the outer most shell of an element is known as valence electron configuration.

It’s easy to write the valence electron configuration for the main group of elements (group 1,2 & 13-18), because the electron present in the electronic shell of the highest principal quantum number are valence electrons and their electronic representation will be easy. For example, the electronic configuration of Cesium (Cs) is 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 5s2 5p6 6s1 so that there is one valence electron in 6s and the valence electron configuration will be 6s1.

But in case of d and f block elements, the valence electron configuration involves the penultimate shell and the ultimate shell also. Hence, the general valence electron configuration of the various blocks is

Element
Valence Electron Configuration
s-block element ns1
p-block element ns2 , np 1-6
d-block element (n - 1)d 1-10,ns 1-2
f-block element (n - 2)f 1-14(n - 1)d 0-1nsa

Electron Configuration Table

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We can show the electron configuration of an element in a tabular form also. Such type of tabular form is termed as electron configuration table. This table describes the number of electrons in each energy level of an atom as well as their arrangement. Electron configuration table is the best way to represent an atom as it shows all the information regarding the energy levels of an atom in a small space.

For example, the electron configuration table for Thallium (Tl) with atom number 81 is given below

1s2
2s2 2p6
3s2 3p6 3d10
4s2 4p6 4d10 4f14
5s2 5p6 5d10
6s2 6p1

Electron Configuration List

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The following table shows the electron configuration chart of the elements of the periodic table.

Atomic Number
Name of element Symbol
Group Electron
Configuration
Symbol, group/series/block and Comments
       1
Hydrogen H
1 1s1
       2 Helium
He
18 1s2 Group 0/18 Noble Gas,
       3 Lithium
Li
1 [He] 2s1 s-block, Group 1 Alkali Metal,
       4 Beryllium
Be 2 [He] 2s2 s-block, Group 2 Alkaline Earth Metal,
       5 Borom B
13 [He] 2s2 2p1 p-block, Group 3/13
       6 Carbon C
14 [He] 2s2 2p2 p-block, Gp4/14,
       7 Nitrogen
N
15 [He] 2s2 2p3 p-block, Gp5/15,
       8 Oxygen O
16 [He] 2s2 2p4 p-block, Gp6/16,
       9 Fluorine F
17 [He] 2s2 2p5 p-block, G p7/17 Halogen,
     10 Neon Ne
18 [He] 2s2 2p6 p-block, Gp 0/18 Noble Gas,
     11 Sodium Na
1 [Ne] 3s1 Gp1 Alkali Metal,
     12 Magnesium
Mg
2 [Ne] 3s2 s-block, Gp2 Alkaline Earth Metal,
     13 Aluminium
Al
13 [Ne] 3s2 3p1 p-block, Gp3/13,
     14 Silicon
Si
14 [Ne] 3s2 3p2 p-block, Gp4/14,
     15 Phosphorus
P
15 [Ne] 3s2 3p3 p-block, Gp5/15,
     16 Sulphur
S
16 [Ne] 3s2 3p4 p-block, Gp6/16,
     17 Chlorine
Cl
17 [Ne] 3s2 3p5 p-block, Gp7/17 Halogen,
     18 Argon
Ar
18 [Ne] 3s2 3p6 p-block, Gp 0/18 Noble Gas,
     19 Potassium
K
1 [Ar] 4s1 s-block, Gp1 Alkali Metal,
     20 Calcium
Ca
2 [Ar] 4s2 s-block, Gp2 Alkaline Earth Metal,
     21 Scandium
Sc
3 [Ar] 3d1 4s2 3d block, not true Transition Metal
     22 Titanium
Ti
4 [Ar] 3d2 4s2 3d block, a true Transition Metal
     23 Vanadium
V 5 [Ar] 3d3 4s2 3d block, a true Transition Metal
     24 Chromium Cr
6 [Ar] 3d5 4s1 3d block, a true Transition Metal
     25 Manganese Mn
7 [Ar] 3d5 4s2 3d block, a true Transition Metal
     26 Iron
Fe
8 [Ar] 3d6 4s2 3d block, a true Transition Metal
     27 Cobalt
Co 9 [Ar] 3d7 4s2 3d block, a true Transition Metal
    28 Nickel
Ni 10 [Ar] 3d8 4s2 3d block, a true Transition Metal
    29 Copper
Cu 11 [Ar] 3d10 4s1 3d block, a true Transition Metal
    30 Zinc
Zn 12 [Ar] 3d10 4s2 3d block, not true Transition Metal
    31 Gallium
Ga 13 [Ar] 3d10 4s2 4p1 p-block, Gp3/13,
    32 Germanium
Ge 14 [Ar] 3d10 4s2 4p2 p-block, Gp4/14,
    33 Arsenic
As 15 [Ar] 3d10 4s2 4p3 p-block, Gp5/15,
    34 Selenium
Se 16 [Ar] 3d10 4s2 4p4 p-block, Gp6/16,
    35 Bromine
Br 17 [Ar] 3d10 4s2 4p5 p-block, Gp7/17 Halogen,
    36 Krypton Kr 18 [Ar] 3d10 4s2 4p6 p-block, Gp 0/18 Noble Gas,
    37 Rubidium Rb 1 [Kr] 5s1 s-block, Gp1 Alkali Metal,
   38 Strontium Sr 2 [Kr] 5s2 s-block, Gp2 Alkaline Earth Metal,
   39 Yttrium Y 3 [Kr] 4d1 5s2 4d block, not true Transition Metal
   40 Zirconium
Zr 4 [Kr] 4d2 5s2 4d block, a true Transition Metal
   41 Niobium Nb 5 [Kr] 4d4 5s1 4d block, a true Transition Metal
   42 Molybdenum Mo 6 [Kr] 4d5 5s1 4d block, a true Transition Metal
   43 Technetium Tc 7 [Kr] 4d5 5s2 4d block, a true Transition Metal
   44 Ruthenium Ru 8 [Kr] 4d7 5s1 4d block, a true Transition Metal
   45 Rhodium Rh 9 [Kr] 4d8 5s1 4d block, a true Transition Metal
   46 Palladium Pd 10 [Kr] 4d10 4d block, a true Transition Metal
   47 Silver Ag 11 [Kr] 4d10 5s1 4d block, a true Transition Metal
   48 Cadmium Cd
12 [Kr] 4d10 5s2 4d block, a true Transition Metal
   49 Indium In 13 [Kr] 4d10 5s2 5p1 p-block, Gp3/13,
   50 Tin Sn 14 [Kr] 4d10 5s2 5p2 p-block, Gp4/14,
   51 Antimony Sb 15 [Kr] 4d10 5s2 5p3 p-block, Gp5/14,
   52 Tellurium Te 16 [Kr] 4d10 5s2 5p4 p-block, Gp6/16,
   53 Iodine I 17 [Kr] 4d10 5s2 5p5 p-block, Gp7/17 Halogen,
   54 Xenon Xe 18 [Kr] 4d10 5s2 5p6 p-block, Gp 0/18 Noble Gas,
   55 Cesium Cs 1 [Xe] 6s1 s-block, Gp1 Alkali Metal,
   56 Barium Ba 2 [Xe] 6s2 s-block, Gp2 Alkaline Earth Metal,
   57 Lanthanum La 3 [Xe] 5d1 6s2 Start of 5d-bock and Lanthanide Series
   58 Cerium Ce 101 [Xe] 4f1 5d1 6s2 1st of f-block in the Lanthanides Metals
   59 Praseodymium Pr
101 [Xe] 4f3 6s2 f-block in the Lanthanides Metals
   60 Neodymium Nd
101 [Xe] 4f4 6s2 f-block in the Lanthanides Metals
   61 Promethium Pm 101 [Xe] 4f5 6s2 f-block in the Lanthanides Metals
   62 Samarium Sm 101 [Xe] 4f6 6s2 f-block in the Lanthanides Metals
   63 Europium Eu 101 [Xe] 4f7 6s2 f-block in the Lanthanides Metals
   64 Gadolinium Gd 101 [Xe] 4f7 5d1 6s2 f-block in the Lanthanides Metals
   65 Terbium Tb 101 [Xe] 4f9 6s2 f-block in the Lanthanides Metals
   66 Dysprosium Dy 101 [Xe] 4f10 6s2 f-block in the Lanthanides Metals
   67 Holmium Ho 101 [Xe] 4f11 6s2 f-block in the Lanthanides Metals
   68 Erbium Er 101 [Xe] 4f12 6s2 f-block in the Lanthanides Metals
   69 Thulium Tm
101 [Xe] 4f13 6s2 f-block in the Lanthanides Metals
   70 Ytterbium Yb
101 [Xe] 4f14 6s2 f-block in the Lanthanides Metals
   71 Lutetium Lu
101 [Xe] 4f14 5d1 6s2 f-block in the Lanthanides Metals
   72 Hafnium Hf
4 [Xe] 4f14 5d2 6s2 d-block element
   73 Tantalum Ta 5 [Xe] 4f14 5d3 6s2 d-block element
   74 Tungsten W 6 [Xe] 4f14 5d4 6s2 d-block element
   75 Rhenium Re 7 [Xe] 4f14 5d5 6s2 d-block element
    76 Osmium Os 8 [Xe] 4f14 5d6 6s2 d-block element
    77 Iridium Ir 9 [Xe] 4f14 5d7 6s2 d-block element
   78 Platinum Pt 10 [Xe] 4f14 5d9 6s1 d-block element
   79 Gold Au 11 [Xe] 4f14 5d10 6s1 d-block element
   80 Mercury Hg 12 [Xe] 4f14 5d10 6s2 d-block element
   81 Thallium TI 13 [Xe]4f14 5d10 6s2 6p1 p-block element
   82 Lead Pb 14 [Xe]4f14 5d10 6s2 6p2 p-block element
   83 Bismuth Bi 15 [Xe]4f14 5d10 6s2 6p3 p-block element
   84 Polonium Po 16 [Xe]4f14 5d10 6s2 6p4 p-block element
   85 Astatine At 17 [Xe]4f14 5d10 6s2 6p5 p-block element
   86 Radon Rn 18 [Xe]4f14 5d10 6s2 6p6 p-block element
   87 Francium Fr 1 [Rn] 7s1 s-block radioactive element from 1st group
   88 Radium Ra 2 [Rn] 7s2 s-block radioactive element from 2nd group
   89 Actinium Ac 3 [Rn] 6d1 7s2 d-block element , 1st element of actinide
   90 Thorium Th 102 [Rn] 6d2 7s2 f-block element , actinide
   91 Protactinium Pa 102 [Rn] 5f2 6d1 7s2 f-block element , actinide
   92 Uranium U 102 [Rn] 5f3 6d1 7s2 f-block element , actinide
   93 Neptunium Np 102 [Rn] 5f4 6d1 7s2 f-block element , actinide
   94 Plutonium Pu 102 [Rn] 5f6 7s2 f-block element , actinide
   95 Americium Am 102 [Rn] 5f7 7s2 f-block element , actinide
   96 Curium Cm 102 [Rn] 5f7 6d1 7s2 f-block element , actinides 
   97 Berkelium Bk 102 [Rn] 5f97s2 f-block element , actinides
   98 Californium Cf 102 [Rn] 5f107s2 f-block element , actinides
   99 Einsteinium Es 102 [Rn] 5f117s2 f-block element , actinides
  100 Fermium Fm 102 [Rn] 5f127s2 f-block element , actinides
  101 Mendelevium Md 102 [Rn] 5f137s2 f-block element , actinides
  102 Nobelium No 102 [Rn] 5f147s2 f-block element , actinides
  103 Lawrencium Lr 102 [Rn] 5f146d17s2 f-block element , actinides
  104 Rutherfordium Rf 4 [Rn] 5f146d27s2 Artificial radioactive element and the first transactinide element.
  105 Dubnium Db 5 [Rn] 5f146d37s2 Artificial radioactive element
  106 Seaborgium Sg 6 [Rn] 5f146d47s2 Artificial radioactive element that does not occur in nature
  107 Bohrium Bh 7 [Rn] 5f146d57s2 Radioactive element
  108 Hassium Hs 8 [Rn] 5f146d67s2 Radioactive element
  109 Meitnerium Mt 9 [Rn]5f146d77s2 Radioactive element

More topics in Electronic Configuration
Reactivity Series Quantum Numbers
Hyperconjugation Aufbau Principle
Valence Electrons Periodic Table Max Planck Quantum Theory
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