Back in 1897, British physicist J.J. Thomson discovered the electron, which, as of then, was the biggest finding of all time.
You have the atom, which has the neutron, the electron, the proton.
Is there a particular reason why an electron weighs as much as it does, or that gravity is as strong as it is?
electron e·lec·tron (ĭ-lěk'trŏn')
A stable subatomic particle in the lepton family having a rest mass of 9.1066 × 10-28 gram and a unit negative electric charge of approximately 1.602 × 10-19 coulomb. Also called negatron.
An elementary particle with a negative charge and a very small mass. Electrons are normally found in orbits around the nucleus of an atom. The chemical reactions that an atom undergoes depend primarily on the electrons in the outermost orbits (the valence electrons).
Note: The movement of large numbers of electrons through conductors constitutes an electric current.
A sub-atomic particle with a negative quantised charge. A flow of electrical current consists of the unidirectional (on average) movement of many electrons. The more mobile electrons are in a given material, the greater it electrical conductance (or equivalently, the lower its resistance).