aufbau principle

[Sharon Rodriguez 3H]

Why does 3d^10 have less energy than 4s^2? Could somebody explain the "switch" in energies that occurs in this area of electron configurations?

[Deana Moghaddas 3E]

The electrons are in a lower energy level (3) as opposed to the higher energy level of 4.

[Leila_4G]

So when we draw the orbital configuration, does 4s go in a row below 3d if we are drawing it vertically with the higher energy levels going up?

[Jasmine Vallarta 2L]

I think of it as

3d vs 4s
n=3 vs n=4
n=3 is in a lower energy level

[ZainAlrawi_1J]

Base it purely off the number order,
3d is n = 3
4s is n = 4
4 > 3
3 is at a lower energy level

[Nyari Muchaka_Discussion 4A]

When you go across the periodic table you come across 3d after 4s, however, in terms of energy levels, you go in numerical order so since 3 is before 4, 3d is lower than 4s. Also pretty sure Lavelle wants us to write the configuration in terms of ascending energy levels.

[Arvind 4G]

The 3d is in the energy level of n=3 which has less energy than the 4s which is in the energy level of n=4.

[Ariel Davydov 1C]

As for writing out electron configurations, Lavelle said that he prefers us to write 3d before 4s, and the same goes for the f-block and other d-orbitals.

[Omar Selim 1D]

There's less energy in the 3rd energy level than the 4th, because of the reality that it takes more energy to maintain stability in the 4th energy level