What is the outermost shell of an atom called?

The outermost shell of an atom is referred to as the valence shell. This shell contains the electrons that are involved in chemical bonding and reactions. The valence electrons, found in this outermost layer, determine how an atom will interact with others, influencing the atom's chemical properties and its ability to form bonds.

In contrast, the nucleus is the dense core of the atom that contains protons and neutrons, playing a fundamental role but does not directly represent the outer shell of the atom. The term "proton shell" is not commonly used in atomic theory; electrons, not protons, occupy shells outside the nucleus. The electron cloud represents the region around the nucleus where electrons are likely to be found, but it is a broader concept that includes all electron shells rather than specifically denoting the outermost one. Thus, the valence shell is the term specifically denoting the outermost layer, essential for understanding chemical reactivity and bonding.