Electronic, bonding, and structural properties of monatomic gold wires containing impurities of atomic hydrogen and carbon have been studied by means of the projector augmented-wave method within the generalized gradient approximation. We find that light impurities cause significant charge redistribution in monatomic gold wires altering bonding and affecting the wire structural properties. Light impurities can drastically promote the parity oscillations of conductance occurring already in pure gold wires, thus demonstrating how the electronic and structural characteristics of nanowires can be tuned by appropriate doping.