The atom was the basic unit of matter that made up everything in the universe. All atoms were held together by electrical charge.
The Bad Wolf entity was powerful enough to destroy the Dalek Fleet attacking Earth in 200,100 by reducing every Dalek and every ship to atoms. (TV: The Parting of the Ways)
Davros had developed and successfully tested a weapon, the reality bomb, capable of cancelling the electric charge that held atoms together. (TV: Journey's End)
Negatively-charged atoms were known as anions. (AUDIO: The Bride of Peladon)