# Wave-Particle Duality: The Beginnings of Quantum Mechanics

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Wave-Particle Duality: The Beginnings of Quantum Mechanics

Explain the basics of wave-particle duality.
Define the relationship between quantum, photon and electron. Describe how a produced line spectra relates to the Bohr diagram for a specific element. Additional KEY Terms Absorption Spectra Threshold energy

PHOTOELECTRIC EFFECT Under certain conditions, shining light on a metal surface will eject electrons. Electrons given enough energy (threshold energy) can escape the attraction of the nucleus. *Light is acting like a “particle” in this experiment – collision.

Can only explain it if you think of it using photons in a collision.
Only high frequency light (> 1.14 x Hz) will eject electrons - acting as particle. Can only explain it if you think of it using photons in a collision.

Only more intense light (higher amplitude) will eject more electrons - acting as wave.
Can only explain it if you think of it as changing the size of the wave.

Photons have no mass but carry a quantum of energy.
Einstein (1905) - electromagnetic radiation is a stream of tiny bundles of energy called photons. Photons have no mass but carry a quantum of energy. One photon can remove one electron. Light is an electromagnetic wave, yet it contains particle-like photons of energy.

Compton (1922) – first experiment to show particle and wave properties of EMR simultaneously.
Incoming x-rays lost energy and scattered in a way that can be explained with physics of collisions.

Quantum Mechanical Model of the Atom

Bohr (1922) – restricting electrons to fixed orbits (n) with different quantized energy levels.
Created a math equation for energy of each orbit. Equations correctly predicted the line colours of hydrogen spectra. Energyn = -(2.18 x J)/n2

Electron absorbs radiation and jumps from
ground state (its resting state) to a higher unstable energy level (excited state). Electron soon loses energy and drops back down to a lower energy level – emitting the absorbed EMR. Absorption Ionization Free Atom e− EMR EMR e− Excited State e− Ground State nucleus > Threshold Energy < Threshold Energy

ΔE = E higher-energy orbit - E lower-energy orbit
= Ephoton emitted = hf

Levels are discrete like quanta – no in between.
Each jump/drop is associated with a specific frequency photon - same transition, same photon.

The size of nucleus will affect electron position around the atom – and the size of “jump” energy.

*Each element has a unique line spectrum as each element has a unique atomic configuration.

Emission spectrum – portion of visible light emitted by that element – cooling down.
Absorption spectrum – portion of visible light absorbed by an element – heating up.

CAN YOU / HAVE YOU? Explain the basics of wave-particle duality. Define the relationship between quantum, photon and electron. Describe how a produced line spectra relates to the Bohr diagram for a specific element. Additional KEY Terms Absorption Spectra Threshold energy