What is the term for the outermost shell of an atom?

The outermost shell of an atom is termed the valence shell. This shell contains the valence electrons, which are crucial for determining how an atom can interact with other atoms. The behavior and properties of an element, including its chemical reactivity, are largely dictated by the electrons in this valence shell. Electrons in the valence shell are involved in bonding and chemical reactions, making this concept fundamental to the study of chemistry and electricity.

The other terms do not accurately describe the outermost shell of an atom. For instance, energy layer could imply a general description of electron shells but does not designate the specific outermost shell. Nucleus layer suggests a focus on the nucleus, which is the center of the atom and contains protons and neutrons, rather than the electron shells. Core shell is not a recognized term for atomic structure and does not appropriately represent the outermost shell where chemical interactions occur.