Ionisation Energy.

Chemistry lessons again,Phew!

Learnt something new:

1)Electronic Configuration(Sub-shell Notation)

2)"Noble Gas" Configuration

For this Configuration thing ,
we have to Remember the 3 RULES of filling up orbitals:

a)Aufbau (building up) principle
-Electrons are placed in the orbital of the lowest energy , then the orbital of the next lowest energy and so on (to give maximum stability to the system).
-The order in which the orbitals are filles:

^
l
l __ __ __ __ __
l 3d
l __
l 4s
l __ __ __
l 3p
l __
l 3s
l __ __ __
l (px)(py)(pz)
l 2p
l __
l 2s
l
l __
1s


The Above Diagrams indicates thats the electron(s) will be filled in the following order:
1s->2s->2p->3s->3p->4s->3d->4p->5s->4d->......


b)Pauli Exclusion Principle

-Each orbital can only hold a maximum of 2 Electrons.

-Both Electrons must be of Opposite spins to each other.
=>WHY? The magnetic attraction which results from their opposite spins can counterbalance the Electrical Repulsion which results from their identical charges.


c)Hund's Rule

-The rules states that in a given energy level,the no. of unpaired electrons should be maximum.

-Pairing of electrons takes place only after all orbitals of the same energy level have been filled with one electron.
=>WHY? By occupying different orbitals, the electrons remain as far away as possible ,thus minimising electron-electron repulsion.


One more IMPORTANT factor to note:
-Electrons occupy the 4s orbital first before filling the 3rd orbitals.
=>WHY?->The 4s is of lower energy than the 3rd orbitals.