This paper narrates the way chemists have been using the electron to account for one of the most intriguing problems, namely the bonding of two neutral atoms to form a molecule. The chemists' attempts to account for the mechanism of the homopolar bond, first in the context of the old quantum theory and after 1926 in the context of wave mechanics, brought the specter of reductionism to physics. We argue that the chemists' successful appropriation of the electron strengthened, first, the autonomy of physical chemistry and, then, of quantum chemistry with respect to physics.