Which particle is not found in the nucleus of an atom?

The electron is the particle not found in the nucleus of an atom. Instead, it orbits the nucleus at various energy levels or shells. The nucleus, on the other hand, is composed of protons and neutrons. Protons are positively charged particles, while neutrons carry no charge. This distinction is essential in understanding the atomic structure because the behaviors of electrons determine chemical properties and bonding interactions, while protons and neutrons define the identity and mass of the atom itself.

The role of electrons as outside the nucleus is fundamental in atomic theory, distinguishing their dynamic interactions within atoms from the more stable, heavier protons and neutrons found at the core.