How is 'Na2' even possible, I really don't understand?

Na2 by itself is not possible. The only place Na2 is a valid notation is in an ionic compound like Na2SO4, where SO4 has a valence of -2, and it therefore takes 2 Na ions, each with a valence of +1, to balance the negative valence. But this doesn't indicate a bonding between the two Na ions, just a bonding of each of them to the SO4 ion.