Wednesday, 18 November 2015

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 2s22p    ( 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) = 1s2s2
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 2s2p3s2 3p1                           Or             [Ne] 3s2 3p1
Si ( z =  14) = 1s2s2 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] 4s3d10 4p5                 
Kr ( z =  36)   = 1s22s22p6 3s2 3p6 4s2 3d10 4p6         Or  [Ar] 4s3d10 4p6                



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