What are the particles in the outermost orbit of an atom called?

The particles in the outermost orbit of an atom are referred to as valence electrons. These electrons are crucial because they are involved in chemical bonding and reactions. Valence electrons determine how an atom will interact with others, such as whether it will gain, lose, or share electrons to achieve a more stable electron configuration. This outer shell is where atoms achieve their desired stability, often through achieving a full outer electron shell, commonly resembling the electron configuration of the nearest noble gas.

The other options pertain to different aspects of atomic structure. Core electrons, for instance, are those that occupy the inner shells and are fully shielded by the valence electrons from the nucleus. Orbital electrons can refer to any electrons present in an atom, not specifically limited to those in the outermost orbit. Terminal electrons is not a standard term used in chemistry to denote specific types of atomic electrons. Therefore, understanding that valence electrons are crucial for bonding and chemical behavior highlights why this choice is the correct answer.