Electron

An electron was a particle. It was one of the components of an atom, along with protons and neutrons. (PROSE: The Infinity Doctors)

Neutrinos would register on a neutrino detector when one interacted with an electron in the fluid inside the detector. (PROSE: The Wheel of Ice)

Photons could be produced by the recombination of an electron and a positron. (TV: Time and the Rani)

An electron and a positron could also be combined to create orthopositronium. (AUDIO: The Time of the Daleks)

The Eleventh Doctor once sent an explanation why electrons have mass to experts of the world to prove he was a genius. (TV: The Eleventh Hour)

A wave interrupter could disable an entire star system by stopping any and all waves, right down to the flow of electrons through a wire. (PROSE: The Book of the Still)

By examining readings from an electron microscope, the Fourth Doctor noticed a change in the electron charge of Eldrad's hand, leading him to the conclusion that it was absorbing radiation. (TV: The Hand of Fear)