University:
Carleton University
Course:
CHEM 1001 | General Chemistry I
Academic year:

2024
Views:

274

Pages:

2
Author:

ali

WAVE THEORY Lecture G1 Electrons are waves Quantum Theory Developed to explain experimental observations that couldn't be understood using the prevailing "classical" theories of physics. Black-body radiation (thermal) Internal energy radiation (heat) Oscillation of charges, EM radiation Planck proposed that energy is quantized: Photoelectric effect: light can eject electrons from a metal, but only if its frequency is above the threshold frequency. Classically, for light as a wave, its energy is proportional to the square of its amplitude. For particles, energy is proportional to frequency. Einstein proposed light has a particle nature as well as a wave nature; i.e., light is quantized (photons). Light is EM radiation that has both wave and particle nature. E = hv = hc/λ Spectroscopic lines - discrete spectral lines Bohr applied quantum theory to the structure of the atom and proposed an atomic model in which the electrons were in discrete orbits. Light emitted by an excited atomic gas consists of discrete lines, not a continuous band. Electrons, with specific, discrete radii and energies, could move in orbit without radiating energy. **Bohr Model** * Explains the line spectrum of hydrogen * As n increases, En approaches the energy of an unbound electron, or 0 **According to classical physics:** * Revolving charged particles should radiate energy. * Thus, e- should spiral into the nucleus. **Bohr's model could only explain the emission spectra of single-electron atoms.** **Bohr could offer no reason why e- should have discrete orbits or energies.** **Matter Waves:** * De Broglie reasoned that momentum (mv) of a particle should be related to h in the same way as a photon. * p = mv = h/λ **Wave-like behaviour + particle behaviour lead automatically to discrete energy levels of electrons.** **Thus, the matter wave concept explains why electrons have discrete energy levels.** **Quantum theory: only describe probabilities.** **Learning Outcomes:** * Calculate the energy of a photon from its wavelength and its wavelength from its energy * Calculate the momentum of a particle from its wavelength and its wavelength from its momentum * Calculate energy levels for one-electron atoms * Relate absorption and emission of photons to changes in energy levels