Which fundamental particle was found to be outside the nucleus?

The electron is the fundamental particle that is found outside the nucleus of an atom. In atomic structure, electrons occupy the space surrounding the nucleus, which consists of protons and neutrons. Protons carry a positive charge, neutrons are neutral, and electrons carry a negative charge. The arrangement of electrons in various energy levels or shells around the nucleus defines the chemical behavior of the atom.

Electrons are much smaller in mass compared to protons and neutrons, making their presence and behavior outside the nucleus crucial in understanding atomic interactions and bonding. This distribution of electrons is fundamental to concepts in chemistry and physics, such as electrical conductivity, ion formation, and the nature of chemical bonds.

In contrast, protons and neutrons reside tightly packed within the nucleus itself, contributing to its mass and stability, but they do not occupy the area outside of it. The positron, which is the antimatter counterpart of the electron, also behaves differently, being involved in processes such as annihilation and pair production, and is not a component of normal atomic structure.