On the periodic table: Why are groups of elements organized by 'letter'

Question

Why are the groups of elements on the periodic table organized into areas represented by the letters s,p,d,f,g, and h? What does this mean?

Letters g and h confuse me a bit. Could you please provide an example of elements that belong to these groups? — andselisk, Jul 10 '17 at 04:13
As far as I know, g is only hypothetical and h doesn't exist. — Verktaj, Jul 10 '17 at 04:21
The s, p, d, and f stand for "sharp," "principal," "diffuse," and "fundamental," respectively. After f comes g,h,i....and so on... — Nilay Ghosh, Jul 10 '17 at 04:26
These areas are called blocks and the letters correspond to the last orbital to be filled by electrons for that block, and they thus exhibit trends or commonalities in chemical properties. Wikipedia gives a pretty good discussion here. — airhuff, Jul 10 '17 at 04:30
This all is just great, spectroscopic notations and stuff, but from the question it looks like OP encountered a PTE with g and h blocks, which I'd really like to look at. — andselisk, Jul 10 '17 at 04:52
Possible duplicate of Periodic table and p block elements, and also of What is SPDF configuration? — Nij, Jul 10 '17 at 04:57

score 11 · Accepted Answer · answered Jul 10 '17 at 04:37

The letters are related to the electron orbitals, which were originally observed through spectroscopy. The lines shown in the spectroscope were named sharp, principal, diffuse and fine (or fundamental).

With a strong magnetic or electrostatic field, these separate into one, three, five or seven lines, or energy levels. There can be up to two electrons (with opposite spin) with the same energy level, according to the Pauli exclusion principle, so this implies there can be double the numbers above, or 2 s electrons, 6 p electrons, 10 d electrons and 14 f electrons. Thus, the Periodic Table is based on the number of electrons in each elements orbitals.

On the periodic table: Why are groups of elements organized by 'letter'

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