4s and 3d orbitals

[Ruohan Sun 3I]

Since 4s orbitals are filled by electrons before 3d orbitals, why are electrons lost from 4s orbitals first?

[jennywu]

According to the Aufbau principle, the 4s sublevel is filled before the 3d sublevel because the 4s is lower in energy. However, when the 3d orbital starts to become filled, the energies of 4s and 3d fluctuate and 4s ends up higher than 3d energy level. so electrons are lost from 4s first.

[Annalise Eder 2L]

The electrons in the 3d orbitals essentially shield electrons in the 4s orbital from the nucleus, so electrons in the 4s orbital are lost first during ionization.

[Jessica Schirmer 1J]

Due to the 4s orbital being filled first, is it important to write the electron configurations like 4s^2 3d^4 for example? Or can it be written as 3d^4 4s^2

[Lindsay H 2B]

it does matter; when writing electron configurations for electrons in the d block, 3d should be written before 4s

[AtreyiMitra2L]

when there are electrons in the 3d orbital, they automatically are of lower energy than 4s. For this reason, even if there are electrons in the 3d orbital, the electrons will be lost from the 4s orbital.