By Carter McBride – Updated March 24, 2022
Determining the number of electron shells, or “rings,” around an atom is straightforward once you know its electron count. Electron shells have a predictable capacity: the first holds two electrons, the second eight, the third eighteen, and so on. By filling shells sequentially, you can identify how many are required for any element.
Consult the periodic table. An element’s atomic number equals its number of protons and, for a neutral atom, its electrons. For instance, neon has an atomic number of 10, so it contains ten electrons.
Calculate a shell’s capacity with the formula 2 × (n²), where n is the shell number. The first shell (n = 1) can hold 2 × 1² = 2 electrons. Subtract this from the total electrons. With neon, 10 – 2 = 8 electrons remain.
Apply the same formula for the second shell (n = 2): 2 × 2² = 8 electrons. Since the remaining electrons equal the shell’s capacity, this shell is full and no electrons are left. Thus, neon has two electron shells.
Repeat the process for elements with more electrons. For example, argon (atomic number 18) would fill two shells (2 + 8 = 10) and require a third shell (capacity 18) to accommodate the remaining eight electrons.
