Question

4s subshell is filled pritor to 3d but on ionization, 4s electrons are removed first. Justify​

Answer 1

It is because, According to the Aafbau principle, the shells with less energy comes first (here, 4s shell has less energy than 3d).

That's why 4s shell comes first, and 3d after it.

But if we talk about the removal of electrons( Ionisation), then, as I mentioned before, 4s shell has less energy than 3d shell, and also having only 2 electrons. And for easy removal, we need less energy to remove any electron, that's why 4s shell having less energy, need less energy to remove electron if compared to the 3d shell. That's why electron of 4s shell are removed first.

Answer 2

Answer:

In elements of 1st transition series

1. 4s-subshell is filled before 3d-subshell, but

2. on ionization, electrons are first removed from 4s-orbital, then from

3d-orbital

Explanation:

1. 4s-subshell is filled before 3d-subshell, because 4s orbital has less energy than 3d orbital and elements of 1st transition series follow Aufbau principle (electrons fill the lower energy atomic orbitals before the higher energy ones)orbital

2. on ionization, electrons are first removed from 4s-subshell and then from 3d-subshell, because the energy of 3d orbital is lower than that of 4s orbital. This is because when electrons are filled in 3d orbital, ENC (effective nuclear charge) increases, resulting in the decrease of energy of 3d orbital.