[Eman7 (OP)]

I read this: "For example, the first energy level has one sublevel and the second has two and so on, in general, the nth energy level has n sublevels." But I thought there are only the four sublevels, which are spdf. So how can the 7th energy level have 7 sublevels when there are only the four sublevels?

Edit: Okay, so I looked it up and there are apparently 7 energy levels. Nevermind.

[chiralSPO]

s, p, d, f, g, h, i...

[evan_au]

I am sure that there are more energy levels beyond those (in fact, an infinite number of them). And some of those levels are populated for a moment when an atom absorbs a photon; but it rapidly drops back to the more familiar levels by emitting one or more photons.

To permanently fill these shells with electrons requires a corresponding number of protons in the nucleus. And nuclei with that many protons disintegrate rapidly, scattering the electrons with them. So these higher energy levels can't be studied quite as conveniently.

[Eman7 (OP)]

Why do they disintegrate?

[chiralSPO]

I personally can't offer a very satisfying answer to "why do heavy atoms disintegrate" but I can point out that as far as we can tell all of the elements heavier than Uranium are radioactive, meaning that their nuclei are unstable. At this point this is all the elements from 93 through 118. It is known that nuclei need to have a one or two neutrons for every proton in the nucleus to stay together (with the exception of the hydrogen nucleus which is only one proton, and cannot break into smaller hadrons). The further from this ideal ratio an atom is, the faster it will fall apart. (https://en.wikipedia.org/wiki/Neutron%E2%80%93proton_ratio#/media/File:Isotopes_and_half-life.svg)

[evan_au]

Why do (heavy nuclei) disintegrate?

The nucleus consists of both protons and neutrons.

• Protons are very small, and have an electric charge. The protons are almost touching; by the inverse square law, this is a lot of force pushing them apart.
• Both Protons and Neutrons feel the strong nuclear force, which is attractive when they are close together. But the largest nuclei start to get larger than the attractive range of the strong nuclear force.
• Neutrons do not have an electric charge, so they act as a "glue" to hold the nucleus together. The larger the nucleus, the more "glue" that is needed to hold them together.
• We are familiar with the concept of electron shells; in a nucleus, the protons and neutrons also fill up shells. When there are far more neutrons than protons, the neutrons fill more shells than the protons, and this reduces stability.

It has been suggested that there may be a few isotopes in a hypothetical "island of stability" heavier than Uranium, but nobody has been able to construct such nuclei in atom smashers. Just as an atom with a ful shell of electrons is more stable, this hypothesis suggests that there may be some nuclei with a full shell of protons and/or neutrons, which would increase stability.