Metals contain free moving electrons, in both the solid and liquid state. Does this happen when it is in vapor form?


Interesting question. There are free electrons and ions in a metal's gas phase, but even at rather high temperatures, they are relatively rare. The formation of free electrons is given by the reaction:

$$\ce {M_{(g)} → M^+_{(g)} + e^{-}_{(g)}}$$

This is an endothermic reaction for all atoms and molecules, and the energy involved receives a special name: the (first) ionization energy. Comparing a chart of ionization energies for the elements, one finds that almost all elements require over $ 500\ kJ/mol$ (or about $5\ eV/atom$) to ionize. Even at $5750\ K$, the temperature of the surface of the Sun, the average thermal energy of a particle is about only about $0.5\ eV$.

Also, a large part of the electrons that did manage to free themselves from their parent neutral atoms would actually be consumed by other neutral atoms, in a different reaction:

$$\ce {M_{(g)} + e^{-}_{(g)} → M^{-}_{(g)}}$$

This reaction is slightly exothermic for most elements and molecules, and the energy associated with it also receives a special name: the (first) electron affinity.

Calculating the equilibrium concentrations of each species at a given temperature is possible but is a bit of work. However, for most metals, you can expect to find significantly less than one free electron per ten thousand neutral atoms at $5750\ K$, and the relative amount of free electrons decreases exponentially with temperature.

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  • $\begingroup$ You are confusing de-localisation with ionisation. Its significant- its present in traditional fluorescent tubes where mercury is vaporised and shortcircuits to give arcs which produce UV- in turn producing fluorescence. $\endgroup$ – user2617804 Dec 9 '13 at 6:11
  • $\begingroup$ @user2617804 I'm considering a thermal plasma in equilibrium, with no applied voltage. Also I'm not sure what you mean about delocalisation. $\endgroup$ – Nicolau Saker Neto Dec 9 '13 at 11:05

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