ABSTRACT
The essential characteristic of the classical atomic particle is its indivisibility, which suggests an associated stability as one of the properties of the building blocks. The ideas of Democritus and the other ancient atomists were, remarkably, put on firm ground thanks to the experimental science of men such as Robert Boyle, Antoine Lavoisier, and John Dalton in the seventeenth through nineteenth centuries. Initial attempts to model the internal structure of atoms assumed that equal numbers of protons and electrons are spread over an entire atomic volume, satisfying electrical neutrality. A heavy, electrically neutral particle was required to contribute the additional mass while keeping the overall electric charge of atoms neutral. Protons and neutrons are known to give mass to the nucleus of a chemical atom. The status of the proton and neutron as “fundamental particles” came under scrutiny.
