Answer:
Quantum theory is much more general than atomic theory. Atomic theory was developed to explain the characteristics of chemical reactions and describes atoms as discrete, indivisible units, with different atoms of the same element identical. Quantum mechanics describes how things at the atomic level and below act. It deals with the fact that atoms are composed of other particles (protons and neutrons in the nucleus and electrons outside). While atomic theory acknowledges the fact that certain atoms will bind together to form compounds, quantum theory describes in detail *how and why* these bonds occur in terms of how the atoms share electrons. Quantum theory is also the basis of our modern understanding of solids, which was not addressed at all in atomic theory.