A friend of mine recently learned of Metallic Hydrogen, such as what we theorize lies beneath the clouds of Jupiter, and thought that hydrogen should be catagorized as a metalloid on the periodic table. We discussed this for some time, with me stating that the periodic table only pertains to elements at room temperature and sea level pressure, and that hydrogen in that state is very non metallic, sharing few, if any, properties with metals. But I wasn't able to convince him, so I have a few questions that I feel should come straight from the experts.
1: What are your thoughts on Metallic Hydrogen, and how similar is it to other metals or metalloids?
2: What causes metallic hydrogen to behave in this way? Hydrogen surely shouldn't have any spare electrons, so what causes the conductivity?
3: Does the periodic table only apply to elements at room temperature and sea level pressure? And if not, could hydrogen be considered a metalloid due to its metallic state?
4: How common is this sort of behavior in elements? Do other elements take on metallic properties or loose them if they are metals/metalloids or do they mostly remain in the same group(ie, alkaline and halogen, or non metal and metals) thoughout their states?(Is gaseous Iron a metal?)
5: The requirements for metallic hydrogen seem to be fairly intense, so even if it could be considered a metalloid, would it ever be made one due to the difficulty in creating the metallic properties?
P.s. No need for lay terms, I'm fairly well versed.