atomic nucleus
Sign in to savecore of the atom; composed of bound nucleons (protons and neutrons)
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The atomic nucleus is the tiny, dense core at the center of an atom made up of protons and neutrons held tightly together. It matters because the nucleus contains nearly all of an atom's mass and determines what element the atom is, making it fundamental to understanding how matter is structured and behaves.
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A model of an atomic nucleus showing it as a compact bundle of protons (red) and neutrons (blue), the two types of nucleons. In this diagram, protons and neutrons look like little balls stuck together, but an actual nucleus (as understood by modern nuclear physics) cannot be explained like this, but only by using quantum mechanics. In a nucleus that occupies a certain energy level (for example, the ground state), each nucleon can be said to occupy a range of locations.
The atomic nucleus is the small, dense region consisting of protons and neutrons at the center of an atom, discovered in 1911 by Ernest Rutherford at the University of Manchester based on the 1909 Geiger–Marsden gold foil experiment. After the discovery of the neutron in 1932, models for a nucleus composed of protons and neutrons were quickly developed by Dmitri Ivanenko and Werner Heisenberg. An atom is composed of a positively charged nucleus, with a cloud of negatively charged electrons surrounding it, bound together by electrostatic force. Almost all of the mass of an atom is located in the nucleus, with a very small contribution from the electron cloud. Protons and neutrons are bound together to form a nucleus by the nuclear force.