L=4 subshell??

Because atoms thus far have not needed to use `g`, `h`, or `i` orbitals. Those are too high in energy and/or are too radially compact to be accessed for now.

`l = 4,5,6` are the `g`, `h`, and `i` orbitals. They are hypothetically known, but practically, the `h` and `i` orbitals won't ever be needed.

We're already at the point where we'd have to synthesize our own heavy elements that are hardly stable...

A `g` orbital would be introduced as a `5g` orbital, which has four angular nodes, and therefore is very radially compact and very high in energy compared to a `6f` orbital.

Thus, it is very easy for electrons to get pushed out of those orbitals due to high-order electron correlation to populate the nearest `f` or `d` orbital instead.

• There are `12` so-called "Aufbau exceptions" in the entire `d`-block: `"Cr, Cu, Nb, Mo, Ru, Rh, Pd, Ag, Pt, Au, Ds, Lr"`, which is within FOUR rows of elements. That's `30%` of the `d`-block.

• There are `10` so-called "Aufbau exceptions" in the entire `f`-block: `"La, Ce, Gd, Lu, Ac, Th, Pa, U, Np, Cm"` (except this is within TWO rows of elements). That's nearly `36%` of the `f`-block.

• You would likely find more "Aufbau exceptions" among such "g-block" elements than you did in the lanthanides and actinides. Perhaps about `42%` of the `g`-block?

These are the `5g` orbitals:

![https://upload.wikimedia.org/]()

whereas these are the `4f` orbitals:

![https://upload.wikimedia.org/]()

An `h` orbital would be introduced as a `6h` orbital, which again is impractical to discuss. Same with `7i` orbitals.