Simple Quantum concept

[Primarygun]

Hello Here I want to ask a few questions and I hope some of you will be kind enough to tell me.

1. My book says the evidence of the sub-shell is from the graph of the pattern of the first ionization enthalpy of the elements.

How does this work? I'm quite opposed since I don't think it is a fair comparison to show that the difference in I.E. is indeed primarily due to the sub-shell.

2. We can find that ionization enthalpy of the sodium atoms by finding the difference between the energy level n=infinity and n=3, right?

3. I glazed at many books very quick in the library and they all only give the first five series of the spectral lines of hydrogen atom, there exists other series, right?

 

Thanks for kind attention