Most of the atoms in the universe
follow this pattern, with protons and neutrons inside the nucleus and
electrons swirling in various states outside of it. Some exceptions to
the rule exist, however, such as hydrogen. The most common isotope of
hydrogen, H1, has no neutrons at all. It consists of only a single
proton in association with a single electron.
Other, more exotic exceptions are possible for the structure of an
atom. Atoms made entirely of antimatter can be synthesized inside of
large particle accelerators. These atoms consist of antiprotons
surrounded by positrons in the place electrons would usually be found.
Apart from their charges, atoms made from antimatter are structurally
identical to atoms of ordinary matter and might behave in similar ways
if they could be kept stable.
Perhaps the most extreme variation on the atomic model is the neutron
star. Neutron stars are stellar remnants that have been so crushed by
their own gravity that electrons within them have been forced to their
surfaces. Essentially, a neutron star is one more configuration an atom
can fall into.This is the best I could tell you, hope it helped
