In terms of structure
What is "natural sodium"? I don't think sodium occurs by itself in nature, only in compounds.
By natural sodium do you perhaps mean NaCl? That's an ionic bonded crystal where the cl takes an electron from the na.
Metallic sodium is all sodium atoms. Each one contributes an electron to the 'sea of electrons'. 1 because a valence electron.
NaCl and metallic Na probably have different crystal structures because of this. NaCl should be 2 interlocking simple cubics and Na should be 1 simple cubic. (I think?). I hated solid state, so crystal structure aren't my expertise.
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