Aufbau (building up ) Principal of electron configuration

How the electrons are arranged in the shells?

Suppose, an atom has no electrons and we are going to fill the electrons in the orbitals of different sub-shells in an atom. This would follow a regular pattern of filling up the orbitals. This is known as  Aufbau  (building up)  principal.

Electrons start to fill from low energy sub-shell and goes on to fill further higher energy sub-shell if there is no. space in low energy sub-shell. Well let’s see……..

Electrons fills in the following pattern:

1s 2s 2p 3s 3p 4s 3d 4p and so on……..

Diagram:

Electrons follow the arrow path in order to fill the orbitals of the sub-shell.

Points to know:

1)  Each orbitals can hold a maximum no. of  2 electrons.

2)  Electrons in an orbital are in opposite to each other.

3) We need to learn about writing the electronic configuration in a more advanced way than  we used to write before :

₆C  : 1s² 2s²2p⁶      ( The no. of electrons in each sub-shell 
                                  are now written as  superscript)

The electronic configuration of first thirty – six are given below:

H ( z = 1)    = 1s¹

He  ( z = 2) = 1s²

Li ( z = 3) = 1s² 2s¹

Be ( z = 4) = 1s²  2s²

B  ( z = 5) = 1s² 2s² 2p¹

C ( z =  6) = 1s² 2s² 2p²

N  ( z = 7) = 1s² 2s² 2p³

O ( z =  8) = 1s² 2s² 2p⁴

F ( z =  9) = 1s² 2s² 2p⁵

Ne  ( z = 10) = 1s² 2s² 2p⁶

Na ( z =  11) = 1s² 2s² 2p⁶ 3s¹                                     Or            [Ne] 3s¹

Mg ( z =  12) = 1s² 2s² 2p⁶ 3s²                                    Or             [Ne] 3s²

Al ( z =  13) = 1s² 2s²  2p⁶  3s² 3p¹                           Or             [Ne] 3s² 3p1

Si ( z =  14) = 1s²  2s² 2p⁶ 3s² 3p²                             Or             [Ne] 3s² 3p3

P ( z =  15) = 1s² 2s² 2p⁶ 3s² 3p³                                Or             [Ne] 3s² 3p3

S ( z =  16) = 1s² 2s² 2p⁶ 3s² 3p⁴                                Or             [Ne] 3s² 3p4

Cl ( z =  17) = 1s² 2s² 2p⁶ 3s² 3p⁵                              Or          [Ne] 3s² 3p5

Ar ( z =  18) = 1s² 2s² 2p⁶ 3s² 3p⁶                             

K ( z =  19) = 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹               Or         [Ar] 4s¹

Ca ( z =  20) = 1s²2s²2p⁶ 3s² 3p⁶ 4s²               Or         [Ar] 4s²

Sc  ( z =  21) = 1s²2s²2p⁶ 3s² 3p⁶ 4s² 3d¹            Or         [Ar] 4s² 3d¹

Ti ( z =  22) = 1s²2s²2p⁶ 3s² 3p⁶ 4s² 3d²               Or        [Ar] 4s² 3d²

V ( z =  23) = 1s²2s²2p⁶ 3s² 3p⁶ 4s² 3d³                Or        [Ar] 4s² 3d³

**Cr ( z =  24) = 1s²2s²2p⁶ 3s² 3p⁶ 4s² 3d⁴        Or        [Ar] 4s² 3d⁴  

Cr ( z =  24) = 1s²2s²2p⁶ 3s² 3p⁶ 4s¹ 3d⁵               Or        [Ar] 4s¹ 3d⁵             

**The reason will be explained in the next blog.

Mn ( z =  25) = 1s²2s²2p⁶ 3s² 3p⁶ 4s² 3d⁵             Or        [Ar] 4s² 3d⁵              

Fe ( z =  26) = 1s²2s²2p⁶ 3s² 3p⁶ 4s² 3d⁶               Or     [Ar] 4s² 3d⁶

Co ( z =  27) = 1s²2s²2p⁶ 3s² 3p⁶ 4s² 3d⁷               Or     [Ar] 4s² 3d⁷

Ni ( z =  28) = 1s²2s²2p⁶ 3s² 3p⁶ 4s² 3d⁸                Or        [Ar] 4s² 3d⁸  

**Cu ( z =  29)  = 1s²2s²2p⁶ 3s² 3p⁶ 4s²3d⁹         Or        [Ar] 4s² 3d⁹

Cu ( z =  29)  = 1s²2s²2p⁶ 3s² 3p⁶ 4s¹3d¹⁰            Or        [Ar] 4s¹ 3d¹⁰

**The reason will be explained in the next blog.

Zn ( z =  30)  = 1s²2s²2p⁶ 3s² 3p⁶ 4s²3d¹⁰                  Or        [Ar] 4s² 3d¹⁰

Ga ( z =  31)  = 1s²2s²2p⁶ 3s² 3p⁶ 4s²3d¹⁰ 4p¹          Or        [Ar] 4s² 3d¹⁰ 4p¹                  

Ge ( z =  32)  = 1s²2s²2p⁶ 3s² 3p⁶ 4s²3d¹⁰ 4p²       Or  [Ar] 4s² 3d¹⁰ 4p²                  

As ( z =  33)  = 1s²2s²2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p³          Or [Ar] 4s² 3d¹⁰  4p³                 

Se ( z =  34)   = 1s²2s²2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p ⁴        Or  [Ar] 4s² 3d¹⁰ 4p⁴                 

Br ( z =  35)   = 1s²2s²2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p ⁵        Or  [Ar] 4s² 3d¹⁰ 4p⁵                 

Kr ( z =  36)   = 1s²2s²2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶         Or  [Ar] 4s²  3d¹⁰ 4p⁶