chapter 5: models of atoms and light rutherford. thomsons atomic model electrons positively charged...
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Chapter 5: Models of Atoms and Light
Rutherford
Thomson’s Atomic Model
Electrons
Positively charged “goo”
A.K.A. the “Plum-Pudding Model”
1910: Ernest Rutherford
• Expert in radiation• Famous “Gold-Foil
Experiment”• Discovered the
presence of the nucleus by firing alpha particles at a sheet of gold foil
Rutherford’s Atomic Model
Electrons
NucleusPositively chargedMade of “protons”
Empty Space
Properties of Light
- Early in the 1900’s, a number of important experiments revealed a close relationship between light and an atom’s electrons
- At this time light was considered to be a form ofenergy that behaves as a wave
- Wave motion can be described by wavelength (), frequency (), and the speed of light (c = 3 x 108 m/s)
Frequency and Wavelength
c = m/s m s-1
Electromagnetic Spectrum
Photoelectric Effect
Refers to the emission of electrons from a metal when light shines on the metal
photoelectric effect demo
Explanation of the Photoelectric Effect
Two German physicists solve the problem of the photoelectric effect.
Max Planck suggested that the light does not emit electromagnetic energy continuously like a wave, but itemits energy in small, specific amounts called quanta.
Planck proposed the following relationship between a quantum of energy and the frequency of radiation:
E = h
E = energy in joules = frequency of radiation emittedh = Planck’s constant (6.626 x 10-34 J s)
Equations You Need To Know
E = h
E = energy in joules = frequency of radiation emittedh = Planck’s constant (6.626 x 10-34 J s)
c = m/s
c = 3 x 108 m/s v= frequency of radiation emitted (s-1) = wavelength (m)m s-1
= c/ E = hc
Explanation of the Photoelectric Effect
Einstein, in 1905, when he wrote the Annus Mirabilis papers
In 1905 Einstein proposed a new radicalidea: light is both a wave and a particle.
Each particle of light carries a quantum of energy and Einstein called these ????
PHOTONS
A photon is a particle of electromagnetic radiation having zero mass and carrying a quantum of energy
The Hydrogen Atom Line-Emission Spectrum
Why had hydrogen given off only specific frequencies of light?
Bohr Model of the Hydrogen AtomDanish physicist Niels Bohr solved the problem of the H-atomemission spectrum in 1913.
The fact that hydrogen atoms emit only specific frequencies oflight meant the energy differences between the atoms’ energystates were fixed
Bohr accounted for these fixed energy states by saying thatelectrons can only circle the nucleus at fixed distances ororbits. Electrons could not exist on the large empty spacebetween these different energy orbits
Bohr Model of the Hydrogen Atom
Bohr’s model could not explain the spectra of larger atoms,nor did it explain the chemical behavior of atoms
However, the idea of discrete energy levels or orbitalswas still an important discovery
Homework Problems For Chapter 5
Page 149-151
22, 24, 27, 31-37, 39-41, 45, 55, 60, 61, 64, 68, 70, 76
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