shell structure

The shell model of an atom describes electrons occupying regions around the nucleus called shells. These shells are assigned a quantum number, n, starting from 1 for the shell closest to the nucleus. Each shell can hold a specific maximum number of electrons: n=1 holds 2, n=2 holds 8, n=3 holds 18, and n=4 holds 32.1

These shells are sometimes labeled with letters, with K representing the first shell, L the second, and so on. The chemical properties of an atom are determined by how its electron shells are filled. For instance, elements like helium and neon are chemically stable because their outermost shells are complete. The outermost shell, known as the valence shell, contains electrons that are least tightly bound and are involved in forming chemical bonds.23