Question

Explain why the 4s sublevel fills before the 3d begins to fill as electrons are added.

Answer 1

Hey there!

Explain why the 4s sublevel fills before the 3d begins to fill as electrons are added.

Electrons occupy orbitals in a definite sequence, filling orbitals with lower energies first. Generally, orbitals in a lower energy level have lower energies than those in a higher energy level. But, in the third level the energy ranges of the principal energy levels begin to overlap. As a result, the 4s sublevel is lower in energy than the 3d sublevel, so it fills first.

Hope this helps

Tobey

Answer 2

Answer: The energy of the 4-s subshell is lower than the energy of 3-d subshell.

Explanation:

During the filling of electrons in subshells, the lower energy levels are filled before the higher energy levels. Also known as Aufbau principle.

Energy of the sublevel = (n + l)

where : n = Principal quantum number

             l = Azimuthal quantum number(s=0,p=1,d=2,f=3)

Energy of 4-s subshell= (4+0) = 4

Energy of 3-d subshell=(3+2) = 5

Energy of 4-s subshell is lower than the energy of 3-d subshell, that is why 4s orbital is filled before the 3-d subshell.