Write down about the Hund .s rule .

Explanation

This rule deal with the filling of electrons into the orbital belonging to the same subshell .
Rule : Pairing of electron in the orbitals not take palce until each orbital belonging to that occupied. In subshelll first one electron arrange and than after pairing will take palce.
There are three p five d and seven f orbitals therefore the pairing of electrons will start in the p , da and f orbitals with the entry of `4^(th), 6^(th)` and `8^(th)` electron respectively.
Example : N (z =7) in `1s^(2) 2s^(2) 2p_(x)^(1) 2p_(x)^(1) 2p_(z)^(1)`
and ` O (z = 8) ` in `1s^(2) 2s^(2) 2p_(x)^(2) 2p_(y)^(1) 2p_(z)^(1)`
type electron configuration occurs.