The excited state electron construction of an atom shows the promotion of a valence electron come a higher energy state.

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

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

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

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


Answer connect
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Truong-Son N.
jan 14, 2016

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

As one example, salt 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 configuration for sodium is:

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

This coincides to an excitation to a an initial excited state that is less stable; the then leader to a relaxation earlier down come the ground state. The be sure emits yellow light (#"589 nm"#).

I end up going through selection rules (which assist you predict even if it is an electronic transition is enabled or forbidden), ax symbols, and also predicting transitions. That overall tells you just how I know that a #3s -> 3p# shift is a real shift for sodium.

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

You might or might not have learned selection rules yet, however they aren"t too difficult to take note of. Castle would help you determine how to compose electron configurations because that excited states.

SELECTION RULES

The an option rules govern just how an electron is observed to transition (excite upwards or relax downwards) indigenous one orbit to another.

Formally, they space 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 also #DeltaJ# is the change in the total angular momentum.

It is valuable to understand the selection rules if you want to predict just how an excited state configuration deserve to be composed just based upon the atom"s (correct) ground state configuration.

EXAMPLES OF digital EXCITATION TRANSITIONS

Allowed:

An example of one allowed digital transition upwards that 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# since for #s#, #l = 0#, and also for #p#, #l = 1#. Thus, #DeltaL = +1#.

#DeltaS = 0# since the electron didn"t get paired v any new electron. It began out unpaired, and it stayed unpaired (#m_s^"new" = m_s^"old"#), therefore #DeltaS = m_s^"new" - m_s^"old" = 0#.

Forbidden:

An example of a forbidden electronic transition upwards that one unpaired electron come an empty 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# since for #s#, #l = 0#, and also for #d#, #l = 2#. Thus, #DeltaL = +2#, i m sorry is larger than is allowed, so the is forbidden.

#DeltaS# is still #0# because it"s the exact same electron transitioning together before, just towards a various orbital.

TERM signs / CONTEXT

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

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DISCLAIMER: The over link explains term signs for context. It help to recognize this, but you don"t need to know this choose the back of her hand unless you room taking physics Chemistry.

APPLICATION the THE choice RULES

Alright, therefore let"s use the an option rules themselves. I gave instances already, so let"s work off of the allowed shift example and readjust it a little bit. The worths for #L#, #S#, and also #J# space pretty similar.

Let us study this energy level diagram because that sodium:

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

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

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Therefore, a typical 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 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 configuration for salt is:

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

And the first excited state electron configuration for salt is:

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

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