An atom is the smallest part of an element bearing the properties of an element. So. the atoms of different elements are different from one another. However, it has been found
that all atoms are comprised of certain fundamental particles (proton, neutron, electron, etc.) that have identical characteristics no matter which atom they belong to.
In nuclear reactors, atoms of heavier elements, like those of uranium and plutonium, get broken when they are bombarded with neutrons.