The excited state electron construction of one atom shows the promo of a valence electron come a greater energy state.

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An electron configuration representing one atom in the excited state will display a valence electron promoted to a greater energy level.

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

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

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


Answer attach
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Truong-Son N.
jan 14, 2016

The first excited state is the very same configuration as the floor state, other than for the place of one electron.

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

The ground state electron configuration for salt is:

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

And the first excited state electron construction for salt is:

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

This corresponds to an excitation come a an initial excited state that is less stable; the then leader to a relaxation back down to the floor state. The relaxation emits yellow irradiate (#"589 nm"#).

I end up walk through selection rules (which assist you predict even if it is an electronic shift is allowed or forbidden), hatchet symbols, and predicting transitions. That in its entirety tells you how I recognize that a #3s -> 3p# change is a real transition for sodium.

(If you want, you can skip the term symbols contextual section; it"s optional.)

You might or may not have actually learned selection rules yet, but they aren"t too challenging to take note of. Castle would aid you determine just how to write electron configurations because that excited states.

SELECTION RULES

The an option rules govern just how an electron is observed to change (excite upwards or relax downwards) indigenous 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 the the electron (spin multiplicity is #2S + 1#), #DeltaL# is the adjust in orbital angular momentum, and #DeltaJ# is the adjust in the total angular momentum.

It is useful to understand the choice rules if you desire to predict just how an excited state configuration have the right to be written just based on the atom"s (correct) ground state configuration.

EXAMPLES OF electronic EXCITATION TRANSITIONS

Allowed:

An instance of one allowed digital transition upwards the one unpaired electron to 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# due to the fact that the electron didn"t gain paired through any brand-new electron. It started out unpaired, and it stayed unpaired (#m_s^"new" = m_s^"old"#), so #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# because 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 quiet #0# because it"s the exact same electron transitioning together before, just towards a different orbital.

TERM symbols / CONTEXT

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

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DISCLAIMER: The above link defines term symbols for context. It help to know this, but you don"t have to know this favor the ago of her hand uneven you room taking physical Chemistry.

APPLICATION of THE choice RULES

Alright, therefore let"s use the selection rules themselves. Ns gave instances already, so let"s job-related off the the allowed transition example and change it a tiny bit. The worths for #L#, #S#, and also #J# room pretty similar.

Let us study this energy level diagram because that sodium:

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You deserve to see lines on the chart going native the #3s# orbit to two #3p# orbital destinations. That indicates either one excitation native the #3s# come the #3p# or a relaxation native the #3p# to the #3s#.

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

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Therefore, a usual excitation/relaxation change 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 prize 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 configuration for salt is:

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

And the first excited state electron configuration for sodium is:

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

Lastly, an easy method to psychic what transitions are permitted is to keep in mind that electronic transitions on energy level diagrams are diagonal, and also involves adjacent columns.