In 1913 Bohr published a theory about the
structure of the atom based on an earlier theory of
Rutherford's. Rutherford had shown that the atom
consisted of a positively charged nucleus, with
negatively charged electrons in orbit around it. Bohr
expanded upon this theory by proposing that electrons
travel only in certain successively larger orbits. He
suggested that the outer orbits could hold more
electrons than the inner ones, and that these outer
orbits determine the atom's chemical properties. Bohr
also described the way atoms emit radiation by
suggesting that when an electron jumps from an outer
orbit to an inner one, that it emits light. Later other
physicists expanded his theory into quantum mechanics.
This theory explains the structure and actions of
complex atoms.
