An element's atomic number defines it. An element with 17 protons will always be chlorine. However an element's mass numbers can vary, which means that it can have different numbers of neutrons ...

The nucleus is very small compared to the atom as a whole: as electrons are even smaller, most of an atom is empty space the diameter of a nucleus can be 100,000 times less than the diameter of an ...

Everyone at that time imagined the atom as a "plum pudding." That is, it was roughly the same consistency throughout, with negatively-charged electrons scattered about in it like raisins in a pudding.

Studying the structure of the atom on smaller scales and being able to produce particles with higher masses is what drove the development of accelerators with ever-higher energies. In a ...