Question

How do quantum number rules dictate periodicity?  

Answer 1

Quantum no:s: - It is a set of 4 no:s with the help of which we can get complete information about all the electrons in an atom. They are : -

1. Principal q. n (n) - main shell in which the electron resides. Max no: of electrons present in the shell (2n2).

2. Azimuthal q.n (l) - no: of subshells present in any main shell. s- subshell , p , d , f

3. Magnetic q.n (m) - no: of orbitals present in any subshell.

4. Spin q.n (s) - direction of electron spin i,e clockwise or anticlockwise .

Modern periodic table states that if the elements are arranged in the increasing order of their atomic no:s , the properties of the elements are repeated after regular intervals. Long form of periodic table consists of horizontal rows called periods & vertical columns called groups. There are 7 periods start with a different q.no: .

Period (n) orbitals filled up electrons to be accommodated no: of electrons

1st n= 1 1s 2 2   

2nd n= 2 2s, 2p 2+ 6 8   

3rd n= 3 3s, 3p 2+ 6 8   

4th n= 4 4s, 3d , 4p 2+ 10+ 6 18

5th n= 5 5s, 4d , 5p 2+ 10+ 6 18

6th n= 6 6s, 4f, 5d, 6p 2+ 14+ 10+6 32

7th n= 7 7s, 5f, 6d, 7p 2+ 14+ 10+ 6 32  

first 3 periods contain ing 2, 8, 8 elements & next 3 periods containing 18, 18 , 32 elements.  

According to Aufbau principle, the electrons are added one by one to the various orbitals in order of their increasing energy starting with the orbital of lowest energy. Order of the orbitals are filled -  

1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f,5d, 6p, 7s, 5f, 6d, 7p .

There are 3 p orbitals in each p- subshell i.e px, py , pz.  

there are 5 d orbitals in each d- subshell i.e dxy, dyz, dxz, dx2- y2 , dz2.