Chapter 5: Models of Atoms and Light Rutherford

Thomsons 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

Rutherfords Atomic Model Electrons Nucleus Positively charged Made of protons Empty Space

Properties of Light - Early in the 1900s, a number of important experiments revealed a close relationship between light and an atoms electrons - At this time light was considered to be a form of energy that behaves as a wave - Wave motion can be described by wavelength ( ), frequency ( ), and the speed of light (c = 3 x 10 8 m/s)

Frequency and Wavelength c = m/sms -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 it emits 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 emitted h = Plancks constant (6.626 x J s)

Equations You Need To Know E = h E = energy in joules = frequency of radiation emitted h = Plancks constant (6.626 x J s) c = m/s c = 3 x 10 8 m/s v= frequency of radiation emitted (s -1 ) = wavelength (m) ms -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 radical idea: 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 Atom Danish physicist Niels Bohr solved the problem of the H-atom emission spectrum in The fact that hydrogen atoms emit only specific frequencies of light meant the energy differences between the atoms energy states were fixed Bohr accounted for these fixed energy states by saying that electrons can only circle the nucleus at fixed distances or orbits. Electrons could not exist on the large empty space between these different energy orbits

Bohr Model of the Hydrogen Atom Bohrs 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 orbitals was still an important discovery

Homework Problems For Chapter 5 Page , 24, 27, 31-37, 39-41, 45, 55, 60, 61, 64, 68, 70, 76