1. Lower n+l  filled first If same n+l  lower n filled first
QUESTION:
In a typical atom, which of these orbitals is filled last? A. 3p, B. 3d, C. 4s, D. 4p
According to the Aufbau principle, the typical order or filling of orbitals can be determined by comparing n+l.
Lower n+l  filled first
If same n+l  lower n filled first
Values of l: l=0 for s; l=1 for p; l=2 for d; l=3 for f
Values of n+l: 3p (3+1=4), 3d (3+2=5),
4s (4+0=4), 4p (4+1=5)
SCRIPT:
In a typical atom, which of these orbitals is filled last?
3p..
3d…
4s…
Or 4p
PAUSE
CLICK
According to the Aufbau principle, the typical order of filling of orbitals depends on the sum of the principal and orbital quantum numbers n and ell.
Orbitals with lower n plus ell value are filled first.
If two orbitals have the same n plus l value, the orbital with the the lower n value is filled first.
CLICK We need to remember that orbital quantum numbers are…
0 for an s orbital
1 for a p orbital
2 for a d orbital
And 3 for an f orbital.
The principal quantum number is the number in the name of the orbital…
N equals 3 for 3p and 3d
N equals for for 4s and 4p
Therefore, the values of n plus ell are: 3+1, or 4 for the 3p orbital
3+2, or 5 for the 3d orbital
4+0, or 4 for the 4s orbital
And
4+1, or 5 for the 4p orbital
Therefore, 3p and 4s
will be filled before 3d and 4p
To break the tie between 3p and 4s, we compare the n values. N=3 for the 3p and n=4 for the 4s
So the 3p is filled before 4s.
Similarly, 3d is filled before 4p.
So the order of filling is 3p first, then 4s, then 3d, then 4p.
The orbital that is filled last is 4p.
We can use the periodic table as a memory aid for remembering the typical order of fililng of orbitals.
The order is
CLICK 1s
CLICK 2s
CLICK 2p
CLICK 3s
CLICK 3p
CLICK 4s
CLICK 3d
CLICK 4p
CLICK 5s
CLICK 4d
CLICK 6s
CLICK CLICK 4f
CLICK 5d
CLICK 6p
CLICK 7s
CLICK CLICK 5f
CLICK 6d
CLICK 7p
PAUSE 2 seconds
END RECORDING

2. 1s 2p 2s 3s 3p 4s 3d 4p 5s 4d 5p 6s * 4d 6p 7s * 5d 7p 4f 5f

3. Video ID: © 2008, Project VALUE (Video Assessment Library for Undergraduate Education), Department of Physical Sciences Nicholls State University Author: Glenn V. Lo Narrator: Funded by Louisiana Board of Regents Contract No. LA-DL-SELECT-13-07/08