Chapter 5: Models of Atoms and Light Rutherford. Thomsons Atomic Model Electrons Positively charged goo A.K.A. the Plum-Pudding Model.

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