Wave-Particle Duality

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Presentation transcript:

Wave-Particle Duality JJ Thomson won the Nobel prize for describing the electron as a particle. His son, George Thomson won the Nobel prize for describing the wave-like nature of the electron. The electron is a particle! The electron is an energy wave!

The Wave-like Electron The electron propagates through space as an energy wave. Electrons exhibit both particulate and wave properties. Louis deBroglie

Another important experiment was the study of the emission of light by excited hydrogen atoms. When a sample of hydrogen gas receives a high-energy spark, the H2 molecules absorb energy, and some of the H-H bonds are broken. The resulting hydrogen atoms are excited; that is, they contain excess energy. They release this energy by emitting light of various wavelengths to produce what is called the emission spectrum of hydrogen. The lowest possible energy state is the ground state.

Spectroscopic analysis of the visible spectrum… …produces all of the colors in a continuous spectrum

When doing experiments with hydrogen gas, it was found that hydrogen atoms emit only specific frequencies of light. The fact that hydrogen atoms emit only specific frequencies of light indicated that the energy differences between the atom’s energy states were fixed. This suggested that the electron of a hydrogen atom exists only in very specific energy states (led to Bohr Model).

Line Emission Spectra

Bohr Model of the Hydrogen Atom Niels Bohr proposed a model of the hydrogen atom that showed that the electron can circle the nucleus only in allowed paths (orbits) (1913).

Bohr Model of the Hydrogen Atom There are three points to be made with the Bohr Model: Bohr designated zero energy as the point at which the proton and electron are completely separated. Ordinarily the hydrogen electron is in its lowest energy state, referred to as the ground state (n=1). When an electron absorbs enough energy, it moves to a higher, excited state. For hydrogen, the first excited state is n=2, then n=3. When an excited electron drops back to its lower energy state it gives off energy as a photon of light.

Electron transitions involve jumps of definite amounts of energy. This produces bands of light with definite wavelengths.

Problem……... Bohr’s model was flawed. We cannot assume that electrons move about in specified orbits. DeBroglie proposed that if light can behave as particles (photons) then electrons can act as waves (wave-particle duality). This led to wave mechanics and the quantum mechanical model of the atom. This differs from the Bohr model, mainly, in that: It is impossible to specify the precise position of an electron in an atom at a given instant.