Accounting for two states of spin, each n - shell can accommodate up to 2 n 2 electrons. Close Privacy Overview This website uses cookies to improve your experience while you navigate through the website. It is not that the principal quantum number can only be measured in integral numbers, it is because the crest of one wave will overlap with the trough of another, and the wave will cancel out. Electron configuration is the distribution of electrons in an atom or molecule. Reversible Reaction Learn.