sorry if this is in the wrong section. the forum rules say a textbook related issue goes here. i'm reading the ashcroft and mermin solid state physics book and referring to page 4. in the context of drude theory, the book states that the valence/conduction electron densities for metals are typically a thousand times greater than those of a classical gas at normal temps and pressures. but i'm confused, how would you calculate such a density for a classical gas. i'm assuming when they say "classical gas" i'm assuming that it is a gas that obeys the ideal gas law. so how would you calculate the CONDUCTION ELECTRON density for air? (the units they are using for this density is "conduction electrons per cubic centimeter") thanks guys.