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Facts about the Nucleus of an Atom for Kids


The nucleus is the very dense region consisting of protons and neutrons at the center of an atom. Almost all of the mass of an atom is located in the nucleus, with a very small contribution from the orbiting electrons.

  • The branch of physics concerned with studying and understanding the atomic nucleus, including its composition and the forces which bind it together, is called nuclear physics.
  • In his plum pudding model, Thomson stated that an atom consisted of negative electronsrandomly scattered within a sphere of positive charge.
  • He reasoned that if Thomson’s model were correct, the immense alpha particles would easily pass through the foil with very little deviation in their paths.
  • Because the mass of alpha particles is about 8000 times that of an electron, it became apparent that a very strong force was present that allowed the particles to be deflected.
  • This configuration is the same as for 1s electrons in atomic orbitals, and is the expected density distribution for fermions (in this case, protons) in 1s states without orbital angular momentum.
  • Protons and neutrons are fermions, with different values of the strong isospin quantum number, so two protons and two neutrons can share the same space wave function since they are not identical quantum entities.
  • Two fermions, such as two protons, or two neutrons, or a proton + neutron can exhibit bosonic behavior when they become loosely bound in pairs.
  • However, the latter type of nuclei are extremely unstable and are not found on Earth except in high energy physics experiments.
  • The residual strong force is a minor residuum of the strong interaction which binds quarks together to form protons and neutrons.
  • The effective absolute limit of the range of the strong force is represented by halo nuclei such as lithium-11 or boron-14, in which dineutrons, or other collections of neutrons, orbit at distances of about ten fermis.
  • Halos in effect represent an excited state with nucleons in an outer quantum shell which has unfilled energy levels “below” it.
  • This formula is successful at explaining many important phenomena of nuclei, such as their changing amounts of binding energy as their size and composition changes (see semi-empirical mass formula), but it does not explain the special stability which occurs when nuclei have special “magic numbers” of protons or neutrons.
  • Another nucleus with 3 nucleons, the triton hydrogen-3 is unstable and will decay into helium-3 when isolated.