The interpreting electronic structure in box notation:

Electron configurations using box notation:

We can represent orbitals as box notations and arrows to represent electrons pair.

Points to know :

•       The electrons pair in any orbitals spin with equal amount of  energy.
•          Electrons are in opposite sides to minimize repulsion to be in high stable conditions.
•          Each orbitals of sub-shell get filled with 1 electron at a time.

represents an orbital

                                                                                                  

                       

 } represents an electron

The electrons configuration of some elements are given below in box notation : 

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

Se ( z =  34)   =     [Ar] 4s² 3d¹⁰  4p⁴  

                

Br ( z =  35)   =   [Ar] 4s² 3d¹⁰  4p⁵  

                

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

               

Stability of sub-shells:-

                                    s >  p > d > f

                                                                                                                   The stability of  sub-shells increases

.i.e. “ s ” sub - shells are the most stable and “ f ” sub – shell are the least stable.

Half – filled “ s ” sub-shell

 

Full – filled “ s ” sub - shell 

Half – filled “ p ” sub-shell

Partially – filled “ p ” sub-shell

Partially – filled “ p ” sub-shell

 

Full – filled “ p ” sub - shell   

Full – filled sub - shell > Half – filled sub-shell  > Partially – filled sub-shell

                                                                                                                            

                                       Stability increases

The reasons behind the electron configurations of Copper and Chromium:

The electronic structure of Copper was supposed to be like this:

**Cu ( z =  29)  = 1s² 2s² 2p⁶ 3s² 3p⁶ 4s²3d⁹         Or        [Ar] 4s² 3d⁹

But Copper’s electronic structure doesn’t exist like that. If we look carefully at the last 3d sub-shell, we can see that it is partially-filled which makes the structure less stable. Since, there is small energy difference between 4s and 3d sub-shell, electrons can move easily from 1 sub – shell to another sub – shell. So, one electron from 4s sub – shell gets promoted to 3d sub – shell.                                                                         

Now, 4s sub – shell is half - filled and 3d sub – shell is full - filled which makes the structure more stable than before.

So, the structure would be :

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

Diagram:

The same thing happens in the case of Chromium:

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

The chromium has 3d sub – shell which is partially – filled. So, one electron from 4s sub – shell gets promoted to 3d sub – shell. Now, this makes both 4s sub-shell and 3d sub-shell half-filled. This is the most stable electronic configuration of chromium.

So, the structure would be :

Cr ( z =  24) = 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹ 3d⁵        Or        [Ar] 4s¹ 3d⁵ 

Diagram: