What particle has a negative charge and is found in the outer shells of an atom?

The particle that has a negative charge and is found in the outer shells of an atom is the electron. Electrons are subatomic particles that occupy the energy levels or shells surrounding the nucleus of an atom. Their negative charge plays a critical role in chemical bonding and interactions between atoms. This is due to their ability to be shared or transferred between atoms, which forms the basis for the creation of molecules and compounds.

Protons, on the other hand, are positively charged particles located in the nucleus of an atom, while neutrons have no charge and also reside in the nucleus. The term "nucleus" refers to the central part of the atom that contains protons and neutrons, and it does not carry a charge itself. Therefore, the characteristics and positioning within the atom specifically make electrons the correct answer for the particle described in the question.