Lithium is known to have the highest ionization energy among Group 1 elements. Also, characteristic colours in the flame test arise due to the excitation and de-excitation of electrons. Then why Lithium gives Crimson Red colour in the Flame test, why not a colour corresponding to a higher frequency like Purple or Blue colour even though the highest amount of energy is involved in the excitation and de-excitation of electrons of lithium when compared to the energy involved in the same process for other Alkali metals?

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    $\begingroup$ Nobody pretends that the color of the flame is due to the transition from the first excited state to the ground state. It may be due to a transition between higher excited states of the Lithium atom. $\endgroup$ – Maurice Apr 4 at 13:09
  • $\begingroup$ @Maurice Does that mean in the case of metals like Caesium the electron can excite to higher orbits and in the case of Lithium the electrons get excited to comparatively less energetic orbits and hence the observation? $\endgroup$ – Chaitanya Garg Apr 4 at 13:22
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    $\begingroup$ Look up “Grotian diagram” and “energy level diagram”. Sodium is a good place to start. The lithium one is also easy to find, so happy searching! $\endgroup$ – Ed V Apr 4 at 13:24
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    $\begingroup$ Instead of «de-excitation», you may use «relaxation», too. $\endgroup$ – Buttonwood Apr 4 at 13:41
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    $\begingroup$ The point is that the emission has nothing to do with ionization. Simple as this. Ions are involved in test flames, but the colour never involves ion-atom transition. It is a transition X* —> X that does not involve a change in charge/oxidation state. $\endgroup$ – Alchimista Apr 6 at 8:29

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