Hello! From what I have understood, there are two different states that an electron can have (Spin up and spin down), and if two electrons are in the same state their wavefunction collapse. So far so good. In a video I saw, they claimed that because of this, only two electrons can exist in the same shell, because after that they need to jump to the next shell, or energy level. I get the idea of it, but I've been taught in school that the shell closest to the nucleus (K-shell) only has two electrons, but that the rest of the shells have eight. I don't doubt this because that's what the periodic table of the elements is built up from, but the thing I don't understand is: How can more than two electrons be in the same shell and therefore in the same state?