aufbau principle

[Aashka Popat 1A]

What is the Aufbau principle and why does the 4s subshell have lower energy than the 3d subshell?

[Micah3J]

Will we need to know the f block for the midterm?

[christabellej 1F]

The Aufbau principle is the building up principle that combines both Pauli Exclusion principle and Hunds rule. Pauli Exclusion principle states that there can be a max of two electrons per orbital and that the two electrons must be spin paired. Hunds rule states that the electrons should be placed one per orbital first in a parallel manner. The 4s subshell only has lower energy if the 3d subshell is not filled yet. Once the 3d subshell has electrons within it, then it has lower energy than the 4s.

[Ashley Tran 2I]

Will we need to know the f block for the midterm?

No, we need to know s, p, and d.

[Robin Cadd 1D]

Anything past the 3d block we don't need to know.