## Building-Up Principle [ENDORSED]

Emi Nakahara 3F
Posts: 21
Joined: Wed Sep 21, 2016 2:57 pm

### Building-Up Principle

I'm a bit confused on how the building-up principle leads to an excited state of an electron, as well as how its excited state configuration compares with its ground state configuration. For example, just from looking at an atom's electron configuration, how can you determine that it is in an excited or ground state?

Yiling Liu 1N
Posts: 25
Joined: Sat Jul 09, 2016 3:00 am

### Re: Building-Up Principle  [ENDORSED]

Hi,

I actually had a similar question but here is a helpful video https://www.youtube.com/watch?v=wS5u2jk6W8Y. By looking at the electron configuration of an atom, you can tell if it is in an excited state if it "jumps" orbitals or begins filling in the next orbital before completely occupying (which means 2 electrons per orbital according to the building-up principle) the previous one.

The explanation I gave above is probably confusing, but the video I watched gives examples that hopefully clarify.

e.g. 1s2 2s2 2p5
This would represent the ground state, since the orbitals filled in order, and the 2p orbital can hold a maximum of 3 orbitals * 2 electrons per orbital = 6 electrons, and there are only 5 for this particular atom. And in fact, this would represent Fluorine, looking at the periodic table.

An example that I just made up:
e.g. 1s2 2s2 2p5 3s1
This would represent the excited state, since the 3s orbital has 1 electron even though the 2p orbital has not completely filled up yet (it can hold a maximum of 6 electrons).

Hope this helps, and hope I'm not getting this wrong...

Emi Nakahara 3F
Posts: 21
Joined: Wed Sep 21, 2016 2:57 pm

### Re: Building-Up Principle

Thank you so much! The video and your examples were very helpful :)

Sophia Eliopulos 2I
Posts: 21
Joined: Wed Sep 21, 2016 2:56 pm

### Re: Building-Up Principle

It helps with practice, but basically you can tell which state it is in by the levels which are filled in an electron configuration.
When in an excited state, the electrons "jump" to a higher level, which is not normally found in the ground state configuration of the atom. This jump causes some energy to be released, hence the term "excited". For Example:

Boron-
Ground State Electron Configuration: 1s22s22p1
Excited State Electron Configuration: 1s22s22p2 or 1s22s22p4

Chlorine-
Ground State Electron Configuration: 1s2 2s2 2p7
Excited State Electron Configuration: 1s2 2s2 2p6 3s1