What is the outer shell of an atom called?

• A. Core shell
• B. Nuclear shell
• C. Valence shell
• D. Electron shell

Answer: (C)

The outer shell is called the valence shell. This is the energy level farthest from the nucleus that holds the valence electrons—the ones most involved in forming bonds and determining an element’s chemical properties. Electron shells are all the energy levels around the nucleus, but the term valence shell specifically refers to the outermost shell where bonding typically happens. For contrast, the nuclear shell is a concept inside the nucleus related to protons and neutrons, and “electron shell” is a general label for any electron layer, not the specialized idea of the outermost, bonding-relevant shell. Atoms with full valence shells (like noble gases) are usually inert because there are no loosely bound electrons to share or transfer.