Failures of Classical Mechanics: Black-Body Radiation & the Birth of Quantum Theory - Prof, Study notes of Chemistry

Download Failures of Classical Mechanics: Black-Body Radiation & the Birth of Quantum Theory - Prof and more Study notes Chemistry in PDF only on Docsity! Classical physics (Newton’s laws of motion) for particles: • Precisely predict the locations and momenta of particles at each instance; • The translational, rotational and vibrational modes of motion can be excited to any energy. Classical Mechanics The electromagnetic spectrum: Classical Mechanics Failures of classical mechanics: • Observation of black body radiation • Heat capacities (for a monotonic solid) • Atomic and molecular spectra • Compton scattering • Photoelectric effect • Optical spectra • Two-slit experiment Heat Capacity Fig. 5. Einstein’s curve fits the experimental data. Dulong-Petit law: The molar heat capacities of all monoatomic solids are ∼25 J K-1 mol-1. Einstein’s theory: Each atom oscillates with a single v, and the oscillation energy is nhv. Experiments: CV 0 when T 0. RC mV 3=, 222 1 3       −      = T T E mV E E e e T RC / / , θ θθ k hv E =θ Atomic and Molecular Spectra Fig. 6. Emission spectra by excited iron atoms. Fig. 7. Absorption spectra of SO2. Fig. 8. Interpretation of spectroscopic transitions. hvE =∆ Photoelectric effect: Wave-Particle Duality Electron diffraction: Evidence for the wave-like character of electrons. Φ−= νhvme 2 2 1 Q1: Calculate the number of photos emitted by a 100 W yellow lamp in 1.0 s. Take the wavelength of yellow light as 560 nm and assume 100% efficiency. The particle character of electromagnetic radiation: