The excited state electron construction of an atom shows the promotion of a valence electron to a greater energy state.

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An electron construction representing one atom in the excited state will present a valence electron supported to a greater energy level.

ExampleThe ground state electron construction of salt is #"1s"^2"2s"^2"2p"^6"3s"^1#.

In that is excited state, the valence electron in the #"3s"# sublevel is promoted to the #"3p"# sublevel, offering the electron configuration as#"1s"^2"2s"^2"2p"^6"3p"^1#.

This is a very unstable condition and the excited electron will certainly drop ago down come the #"3s"# sublevel, release the very same amount of power that was absorbed, and also producing a characteristic color of light, in this situation yellow.


Answer connect
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Truong-Son N.
jan 14, 2016

The very first excited state is the exact same configuration together the floor state, other than for the position of one electron.

As an example, sodium goes through a #3s -> 3p# transition.

The ground state electron construction for sodium is:

#color(blue)(1s^2 2s^2 2p^6 3s^1)#

And the first excited state electron construction for sodium is:

#color(blue)(1s^2 2s^2 2p^6 3p^1)#

This synchronizes to one excitation come a first excited state that is less stable; that then leads to a relaxation earlier down to the floor state. The relaxation emits yellow light (#"589 nm"#).

I finish up walking through selection rules (which help you predict whether an electronic change is enabled or forbidden), term symbols, and predicting transitions. That overall tells you just how I know that a #3s -> 3p# shift is a real change for sodium.

(If friend want, you have the right to skip the term signs contextual section; it"s optional.)

You may or may not have actually learned selection rules yet, yet they aren"t too challenging to take note of. Lock would assist you determine just how to write electron configurations for excited states.

SELECTION RULES

The selection rules govern exactly how an electron is observed to change (excite upwards or relax downwards) from one orbit to another.

Formally, they are written as:

#color(blue)(DeltaS = 0)##color(blue)(DeltaL = 0, pm1)#

#color(blue)(L + S = J)#

#:. Color(blue)(DeltaJ = 0, pm1)#

where #DeltaS# is the adjust in intrinsic angular momentum of the electron (spin multiplicity is #2S + 1#), #DeltaL# is the adjust in orbital angular momentum, and also #DeltaJ# is the readjust in the total angular momentum.

It is advantageous to understand the an option rules if you desire to predict just how an excited state configuration have the right to be created just based upon the atom"s (correct) ground state configuration.

EXAMPLES OF digital EXCITATION TRANSITIONS

Allowed:

An instance of an allowed digital transition upwards of one unpaired electron come an empty orbital:

#color(green)(2s -> 2p)# (#color(green)(DeltaS = 0#, #color(green)(DeltaL = +1)#, #color(green)(DeltaJ = 0, pm1)#)

#DeltaL = +1# due to the fact that for #s#, #l = 0#, and also for #p#, #l = 1#. Thus, #DeltaL = +1#.

#DeltaS = 0# because the electron didn"t obtain paired through any brand-new electron. It began out unpaired, and it remained unpaired (#m_s^"new" = m_s^"old"#), for this reason #DeltaS = m_s^"new" - m_s^"old" = 0#.

Forbidden:

An example of a forbidden electronic transition upwards the one unpaired electron come an north orbital:

#color(green)(3s -> 3d)# (#color(green)(DeltaS = 0)#, #color(green)(DeltaL = color(red)(+2))#, #color(green)(DeltaJ = 0, pm1, color(red)(pm2))#)

#DeltaL = +2# due to the fact that for #s#, #l = 0#, and also for #d#, #l = 2#. Thus, #DeltaL = +2#, which is larger than is allowed, so the is forbidden.

#DeltaS# is still #0# due to the fact that it"s the same electron transitioning as before, simply towards a various orbital.

TERM icons / CONTEXT

"I"ve never ever seen #L#, #S#, or #J# before. Huh? What are they supplied for?"

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DISCLAIMER: The above link explains term signs for context. It help to know this, but you don"t need to know this like the ago of your hand unless you are taking physics Chemistry.

APPLICATION of THE choice RULES

Alright, so let"s use the choice rules themselves. Ns gave examples already, for this reason let"s job-related off that the allowed transition example and readjust it a tiny bit. The worths for #L#, #S#, and #J# are pretty similar.

Let us research this energy level diagram for sodium:

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You deserve to see lines on the diagram going from the #3s# orbital to 2 #3p# orbital destinations. That suggests either an excitation indigenous the #3s# come the #3p# or a relaxation indigenous the #3p# come the #3s#.

These 2 lines are marked #589.6# and #589.0#, respectively, in #"nm"#, for this reason what you watch happening is that sodium provides its #"589 nm"# excitation change (upwards), and also then relaxes (downwards) to emit yellow light.

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Therefore, a typical excitation/relaxation transition sodium makes is:

Excitation Transition: #3s -> 3p# (#DeltaS = 0#, #DeltaL = +1#, #DeltaJ = 0, +1#)

Relaxation Transition: #3p -> 3s# (#DeltaS = 0#, #DeltaL = -1#, #DeltaJ = 0, -1#)

(Term price notation:

#""^2 S_"1/2" -> ""^2 P_"1/2", ""^2 P_"3/2"#, excitation

#""^2 P_"1/2", ""^2 P_"3/2" -> ""^2 S_"1/2"#, relaxation)

So the ground state electron construction for sodium is:

#color(blue)(1s^2 2s^2 2p^6 3s^1)#

And the first excited state electron construction for sodium is:

#color(blue)(1s^2 2s^2 2p^6 3p^1)#

Lastly, one easy means to mental what transitions are permitted is to keep in mind that electronic transitions on energy level diagrams space diagonal, and also involves nearby columns.