Atom to the positively charged nucleus by the attraction created from opposite electric charges. If an atom has more or fewer electrons than its atomic number, then it becomes respectively negatively or positively charged as a whole; a charged atom is called an ion. Electrons have been known since the late 19th century, mostly thanks to J.J. Thomson; see history of subatomic physics for details. Protons have a positive charge and a mass 1,836 times that of the electron, at . The number of protons in an atom is called its atomic number. Ernest Rutherford (1919) observed that nitrogen under alpha-particle
A Is for Atom tighter editing, new music and a focus on nuclear power as opposed to nuclear bombs. A narrator is relating what is an atom and how atomic energy can be harnessed by man to produce "limitless" energy. Dr. Atom (a caricature with an atom for a head) then explains the similarities between the solar system and atomic structure. He then goes on to relate how the atom is made up of protons, neutrons, and electrons. After this, the narrator explains how there are more than 90 elements with many possible isotopes for each. The history of atomic energy is then overviewed