Electron configuration

[Sisam Bhattarai 2C]

When calculating the electron configuration with an element with a charge that enters the d shell why do we subtract from the s first?

[Gabrielle Arreglo 3F]

Having e- in d subshell means that the e- in the s subshell are higher. If you wrote out the e- configuration for atoms with d subshells, it will end with []nd^xns^2, so you take away the electrons that already have the highest energy.

[Averie Moore 2F]

Electrons in the d orbital are lower energy than those in the s orbital. We subtract from the s orbital first because it is closest in energy to the d orbital and electrons would rather be at a lower energy state.

[Jasmin 2C]

We subtract from s rather than d because s has a higher energy and it would be unstable to subtract from the d orbital.
Having 3d^104s^1 is more stable than 3d^94s^2. It all comes down to stability.