Electron Configuration
★ Learning Target - Be able to write the electron configuration for any element.
There can only be two electrons in each orbital!
Electrons are filled in from lowest energy, to highest. This image shows the electrons in the first 3 energy levels.
But, according to Aufbua's Principle, electrons don't always behave like this. The will actually fill in in this order.
Notice, after 3p, you would expect it to move to 3d. But since 4s is actually lower energy than 3d, 4s is filled first.
This is the diagonal rule for electron filling. It shows the order that electrons will fill in orbitals, from lowest energy, to highest energy. This would a great diagram to put on your periodic table!
The periodic table is also organized based on energy levels.
Label your periodic table so that it's organized in blocks as well.
All the 1st and 2nd groups (as well as He) are part of the s-block.
The transition metals (groups 3-10) are part of the d-block.
Groups 13-18 (minus He) are part of the p-block.
The lanthanides and actinides are part of the f-block.
Now that you know which elements are members of which block, you can actually use your periodic table to calculate electron configuration.
Here is the electron configuration for Silicon.
Pay attention to the last electron for each element's configuration.
It tells you what element it is.
NEON:
last electron is 2p⁶.
this tells you its in the 2nd period (energy level).
this tells you its in the p block.
this tells you its the sixth element in the p-block.
Watch the video below to master writing electron configurations for any elements.