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The flame test colors for alkali metal and alkaline earth metal salts are well known, but what about the metals themselves? Do they also give rise to the same colors (eg, brick red for Ca, pale green for Ba etc), or does it differ? And if so, why?

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Yes, the metals, when sent in a flame produce the same colors as their salts. In fact, the metallic ions do not produce any color when sent in a flame. It is only the neutral atom that produce the famous yellow double line of the sodium. This means that a tiny amount of the $\ce{Na+}$ and $\ce{Cl-}$ ions are first transformed into neutral $\ce{Na}$ and $\ce{Cl}$ atoms. And the color of the flame is due to the deexcitation of these rare atoms being first electronically excited in the flame. So it means that the following processes are occurring successively in the flame:$$\ce{NaCl(s) -> Na(g) + Cl(g)}$$ $$\ce{Na + heat -> Na^*}$$ $$\ce{Na^* -> Na + h\nu }$$ The famous yellow light of the $\ce{Na}$ atom is due to the return of the outer electron from the level $4s$ to $3p$ of the sodium atom, if my memory is good. Nothing to do with the $\ce{Na+}$ ion.

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  • $\begingroup$ Why does caesium, a pretty large atom, need high-energy blue light to get excited but lithium, a small atom whose nucleus tugs strongly at the outermost electrons, need low-energy red light? $\endgroup$ Mar 23 '21 at 9:50
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    $\begingroup$ The visible light emitted by these atoms is not always the return of the electron to the lowest level. It is even rarely the case. It may be the passage from a very high excited level to a not so high excited level. $\endgroup$
    – Maurice
    Mar 23 '21 at 10:12
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    $\begingroup$ @RayBradbury and what we see is the energy of the jump, not the energy of the levels themselves. $\endgroup$
    – Alchimista
    Mar 23 '21 at 14:31
  • $\begingroup$ I suggest changing the dot to an asterisk. $\endgroup$
    – Alchimista
    Mar 23 '21 at 14:32
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    $\begingroup$ @RayBradbury In addition to the comment by Maurice, there is another reason the colour you see has little to do with the energy of different orbitals: you only see lines in the visible but many emission lines are UV or IR so you usually see only a small selection of the actual range of emission lines. $\endgroup$
    – matt_black
    Mar 23 '21 at 17:20

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