Order of Subshell Filling (Aufbau Principle)
When writing electron configurations or orbital diagrams for a given element or ion, you must fill the orbitals with electrons in the correct order.
The correct order is as follows:
1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f 6d 7p 6f 7d 7f
There are several ways that you can use to remember the order of filling.
• In one trick, you list horizontally each subshell in a given principal energy level, keeping each principal energy level separate. Then, you zigzag up or down through the rows at an angle:
• If you are musical, you can learn the “Aufbau Song” to remember the order of filling.
do re me fa so la ti 1 2 3 4 5 6 7
Treble Clef
Bass Clef
OR
*The EASIEST WAY though, might be to visualize your Periodic Table as being in “blocks” in which a specific type of orbital (s, p, d, or f) is being filled. *Note the exceptions for chromium, molybdenum, copper, and silver.
Also be aware that the Lanthanide series (*) is separated out from the Periodic Table, so the order of filling for Period 6 is 6s, 4f, 5d, 6 p
Likewise, the Actinide series (†) is separated out, so the order of filling for Period 7 is 7s, 5f, 6d
Use the method that makes the most sense and is easiest to use.
Happy electron configuration writing!