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Chapter 8.1-8.6

CHEM 112 Chapter Notes - Chapter 8.1-8.6: Louis De Broglie, Hydrogen Atom, Photon


Department
Chemistry
Course Code
CHEM 112
Professor
Gang Wu
Chapter
8.1-8.6

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Chemistry Week 2
8-2
Prelude to quantum theory
Blackbody radiation
o Light emission by heating of solids
Energy is discontinuous
A quantum of energy the difference between any two allowed energies of a system
Plak’s ostat = 6.66x-34J
The photoelectric effect
o When light hits the surface of certain metals, an electron is ejected
o Number of electrons is dependent on intensity but energy of electrons is dependent on frequency
o Albert Einstein determined that particles of light are called photons
o Photons hit electrons and electrons absorb the energy and photoelectron is released
o Light intensity is associated with number of photons arriving per time
Atomic emission spectra
o Visible light is said to be a continuous spectrum because light being dispersed consists of many wavelength components
o If light only has a small number of wavelength components, then it is a discontinuous spectrum
o The emitted light of an element (gas flame) has a distinct number of wavelength components observed as coloured lines and dark spaces
between them
o Called atomic or line spectrum
The Bohr Model
o Hydrogen atom
Electron moves about the nucleus with speed in one of a
set circular orbital. When it stays in the orbital, no
energy is emitted
The angular momentum is an interger
An atom emits energy as a photon when an electron
falls from orbit of a higher energy to a lower energy
8-3
Energy levels, spectrum and ionization energy of a hydrogen atom
The electron in a hydrogen atom is found in the lowest energy level, n=1
Called ground state
As an electron gains energy then it moves to a higher level (excited state)
When the electron drops back to ground state, a unique quantity of energy is
released and a specific wavelength is produced and observed as specta lines
Absorbtion spectroscopy is used to determine an element (kinda)
Ionization energy of hydrogen and hydrogen-like ions
8-4
The two leading ideas in quantum mechanics
Wave particle duality
o Louis de Broglie considered the nature of light and matter
o Proposed that small particles of matter may at times display wave-like properties

o Theory proposed that at times, particles of matter have wavelike properties and sometimes they have particular properties
The uncertainty principle
o We cannot predict the exact speed and position of a particle at the same time
o Also known as the Heisenberg principle
o We are able to know the speed of a particle but not its position, or the position but not the speed\
 

8-5
Standing waves
Travelling waves when crests and troughs travel great distances
Standing waves oscillate between two fixed points and do not oscillate on certain points called nodes
Wavelengths of standing waves are quantized   
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