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I've read many times that in metals (for example sodium metal), what constitutes the crystal lattice is an arrange of atoms, since no electron is given or lost, they are just shared between all the atoms within the structure.

In other texts though, it is written that metallic bonding is comprised of cations "surrounded" by free electrons since electrons are not held to the nucleus as in a single metal atom in the gas phase. From a formal point of view, which of the two statements is correct? Does it make a difference to consider cations or atoms when describing metallic bonding?

Which is the more appropriate terminology?

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    $\begingroup$ Well, the solid state physics is more complex than either... $\endgroup$ – Jon Custer Jun 18 '18 at 15:29
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    $\begingroup$ At an introductory level, the two really aren’t that different. An atom sharing electrons isn’t conceptually that different from cations surrounded by the free electrons. $\endgroup$ – Jon Custer Jun 18 '18 at 15:41
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    $\begingroup$ chemistry.stackexchange.com/a/8082/9961 $\endgroup$ – Mithoron Jun 18 '18 at 17:51
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    $\begingroup$ At least in solid state physics and materials science we would say that atoms sit on lattice sites. Unless, particularly for a polar compound, you want to distinguish between anions and cations. But for a metal, just say atoms... $\endgroup$ – Jon Custer Jun 18 '18 at 18:20
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    $\begingroup$ Also, though there is a "sea" of free valence electrons, they pretty much stay in position around the atoms. If you apply an electric current across a metal, for every electron added, at the negative side, one pops out by the positive. The actual drift velocity of the electrons is quite slow, though the wavefront travels at the speed of light (in the metal). $\endgroup$ – DrMoishe Pippik Jun 19 '18 at 1:41
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Both your statements mean the same thing, however it is convenient to think of metals as kernel + sea of electrons, as it greatly simplifies visualization, conceptualization and thus calculations. From a purely numeric viewpoint, i prefer the 'sea of free electrons' model or that cations are surrounded by free electrons.

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