Many thanks guys. I know my questions must sound bizarre sometimes but its really good when I get answers and info like that.

So basically it appears like is there is some fundamental atomic structure which electrons fill 'from the bottom up' if you like, not being able to inhabit exactly the same 'slot' as an existing electron. To [over] simplify it, when n is say, 1, there are are two slots available each with a different spin (l and m are both zero). If only one of these two 'spin' slots are filled you have Hydrogen, if the other one is filled then you have Helium. For the atom to have another electron it would have to have enough energy to leap to the n=2 shell, starting the next line of the periodic table. And so on increasing as each shell has more capacity due to more 'slots' of orientation and gemoetry being available within a fundamental structure that follows an established set of rules. That side of it seems kind of natural - even if 'slots' being taken by probability wave clouds is a bit bizare.

What I'm curious about it why is it assumed that n cannot have a negative value ? Is it that there is then a specific reason why that defies sense ? Is it because at some stage that would produce complex numbers in Schrodinger's equation ? or is it just because no element has been seen where n is below the zero point ? Or something else more specific ?

Again I appreciate its probably a stupid question but this is buggin me right now.