What is contained in the nucleus of an atom?

The nucleus of an atom is composed of protons and neutrons. Protons are positively charged particles, while neutrons carry no charge. Together, these particles account for the majority of the atom's mass. The protons determine the atomic number, which defines the element, and the neutrons contribute to the atomic mass but do not affect the charge of the atom.

Electrons, on the other hand, are found outside the nucleus in electron shells or energy levels. They are negatively charged and orbit around the nucleus, thereby not being part of the nucleus itself. The presence of protons and neutrons within the nucleus is what gives rise to the stability and structure of the atom, which is critical for understanding atomic interactions and chemical bonding.

Understanding the composition of the nucleus is fundamental in fields like chemistry and physics, as it lays the groundwork for concepts such as isotopes, nuclear reactions, and the behavior of materials at a microscopic level.