Hydrogen is unique among the elements because it consists of only one electron and one proton in its nucleus. As a result, hydrogen has only one shell available for its outermost valence electron.
In the Bohr model of the hydrogen atom, which is a simplified model, electrons occupy discrete energy levels or shells around the nucleus. These energy levels are labeled as n = 1, 2, 3, and so on, with n representing the principal quantum number. The energy levels farther from the nucleus have higher energies.
For hydrogen, with only one electron, this electron occupies the lowest energy level, which is the n = 1 shell, often referred to as the K-shell. The n = 1 shell can accommodate a maximum of 2 electrons.
However, it's important to note that hydrogen can also exhibit properties similar to elements with more than one valence shell, particularly in chemical reactions and bonding. Hydrogen can gain or lose an electron, forming the hydride ion (H-) or the proton (H+), respectively. In these cases, hydrogen can exhibit characteristics similar to other elements in terms of its valence shell occupancy.