Is the number of electrons in the electron shell of an atom determined?

The chemical elements known to mankind are contained in the table, which was created by the famous scientist Dmitry Mendeleev. In the table, the elements are arranged in accordance with certain principles and patterns. One of the features is the number of electrons located inside the electron atomic shell. In accordance with the general rule in chemical science, the number of electrons in an atom, as well as the number of protons, is determined by the ordinal number of a chemical element in the above table.