Lower in Energy? [ENDORSED]

[RuchaDeshpande1L]

When asked which orbital is lowest in energy, should we look at the principal quantum number (n) or angular momentum quantum number (l, determines whether s,p,d,etc subshell)? As in, would 3d be lower in energy, or would 4s be lower?

[Vincent Kim 2I]

Typically we look at the principal quantum number to determine which orbital is lower in energy, but in the case of 3d and 4s, 4s is lower.

[Annalise Eder 2L]

The quantum number n gives the energy level while the angular momentum quantum number tells you the subshell of the electron. So use n as l does not give you information about the energy level. For potassium and Calcium 4s has lower energy than 3d which may seem counterintuitive, but for Scandium through Zinc 3d is slightly lower in energy than 4s.

[Bansi Amin 1D]

3d is higher in energy than 4s when the d orbital is empty. When 3d has an electron in it, 3d becomes lower in energy than 4s.

[Rithik Kumar 3E]

If we consider an elementary model of atoms and their quantum structure I believe we should use the principal quantum value or the "n value" to determine the relative levels of energy. However, it should be taken into consideration that, for example, the 3d orbital is higher in energy than the 4s orbital until it gains an electron.

[Kailie_Giebink_1E]

in chemistry is everything is relative to the problem? or is there a hard rule to follow here?

[Chem_Mod]

Bansi's answer is what you would consider a "hard rule" and is correct. :)