Final answer:
The theory of wave-particle duality is a core concept in quantum mechanics stating that every particle exhibits both wave and particle properties, influencing the understanding of the behavior of atoms and subatomic particles.
Step-by-step explanation:
The theory of wave-particle duality is a fundamental principle of quantum mechanics. It suggests that all matter exhibits properties of both waves and particles. This dual behavior can be observed in phenomena such as the diffraction and interference patterns, which demonstrate wave properties, and the photoelectric effect, showing particle characteristics. Atomic particles, such as electrons, exhibit this duality; they can act like waves under certain experimental conditions, quite distinct from their particle-like behavior in others. The wave-particle duality is a conceptual framework that helps us understand how light and matter can display properties of both waves and discrete particles depending on how we observe and measure them.