# Why do groups in the periodic table have missing periods? [duplicate]

What is the reason for skipping groups in the periodic table?

To word this another way: why isn't the electron configuration of Vanadium defined as 1s2 2s2 2p6 3s2 3p6 3d5 instead of 1s2 2s2 2p6 3s2 3p6 3d3 4s2? What causes the jump to the fourth group instead of filling out the third group first?

Along a similar line of reasoning I have a few more questions:

Is Nitrogen the most potentially spin-polarizable element (that is, having the most valence elections in the same orbital) with its 1s2 2s2 2p3 configuration?

Do the outermost s1 and s2 electrons block an outside observer from measuring the larger inner group orbitals for elements heavier than Nitrogen (for instance, would Chromium's 4s1 electron or Manganese's 4s2 electrons prevent you from detecting the spin of the 3d5 electrons in either case?)

Is there any relation in discernible properties between an s, p, d, f, g orbital electron with the same spin (in other words, say every partially-filled shell is spin polarized, would you be able to detect an all-up or all-down configuration of 3d5 4s1 in an atom of Manganese vs an atom of Manganese with either an up spin on 3d5 and down spin on 4s1 or a down spin on 3d5 and an up spin on 4s1?)