Chapter 5- Where is the electron found?

Different types of spectra Continuous spectra from incandescent light bulb Line emission spectrum of Hydrogen Line emission spectrum of Sodium Line emission spectrum of Mercury

Neils Bohr Bohr treated the electron as only a particle, like dust. This electron orbits the nucleus in discrete paths. ”planetary model” “Anyone who is not shocked by quantum theory has not understood it.”

Electrons in lowest energy states= ground state When energy is added, electrons can be promoted to higher energy states= excited. Light (as photons) is emitted when an electron returns to the ground state= emission spectrum

ground state: e- in lowest possible energy excited state: e- gains energy, moving to a state where atom has more energy in an excited state, e- releases specific quantity of energy as it “falls” back to ground state. An electron in a hydrogen atom can move between only certain energy states, shown as n = 1 to n = 7.

Bohr’s model explained the Hydrogen atom well, but not others Bohr’s model explained the Hydrogen atom well, but not others. Further experiments clouded the atomic model….

Quantum Model Modern model of the atom Electrons can be found in orbitals or “electron clouds” Quantum model, or modern model, can also be called the “electron cloud model”

Evolution of the atomic model

Evolution of the atomic model Bohr model of the atom= electrons reside in “orbits” around the nucleus, only certain “orbits” are allowed, like RUNGS on a ladder.

Evolution of the atomic model Quantum model of the atom= electrons are in an “electron cloud”. Their exact location is not known.

                                                                                                    <> http://htwins.net/scale2/

48 Iron Atoms on a Cu surface “Quantum Corral” Circa 1985 Scanning Tunnelling Microscopy Image “The ripples in the ring of atoms are the density distribution of a particular set of quantum states of the corral.” http://www.almaden.ibm.com/vis/stm/corral.html#stm7

2. Where are the electrons? We don’t know, for sure. As soon as we try to measure the location of the electron, we are DISTURBING the system. Also, if an electron is a wave and a particle, How do we measure it? We are forced to speak in PROBABILITIES instead of CERTAINTIES.

Einstein explains the Photoelectric effect,1905 When light is shone on clean metal surfaces in vacuum, electricity is produced. Only certain types (wavelengths) of light create electricity. ELECTRONS have particle behavior. The number of electrons emitted by the metal depends on the intensity of the light beam applied on the metal;  more intense the beam, higher the number of electrons emitted. The emitted electrons move with greater speed if the applied light has a higher frequency. No electron is emitted until the light has a threshold frequency, no matter how intense the light is.

Louis deBroglie ,1924 Electrons could be considered as waves confined to the space around a nucleus http://www.spaceandmotion.com/quantum-theory-de-broglie-quotes.htm

•••••••• Thus, electrons AND light display the WAVE-PARTICLE DUALITY OF LIGHT AND ELECTRONS ••••••••

So, light and electrons can be a particle AND a wave? Light and electrons behave like waves as they diffract and interfere (Louis De Broglie) Light and electrons behave like particles in the photoelectric effect and emission spectra. So the compromise is that they are BOTH!

Summary videos http://www.youtube.com/watch?v=xqNSQ3OQMGI http://www.youtube.com/watch?v=-YYBCNQnYNM

Erwin Schrodinger Made calculations of electron behavior describing it as a wave function, ψ (psi). Electrons are in probable locations known as electron clouds. “Schrodinger’s cat” paradox Paradox=a statement that may be true but seems to say 2 opposite things. Something full of contradictions.

Demo grating on overhead, spectrometers with gas discharge tube, flame tests In 1802 Spectral lines from the sun were see by William Wollaston.A German optician names Joseph von Fraunhofer observed and cataloged the lines in 1814, measuring the positions of the lines. In 1850 Gustav Kirchoff investigated further, with the help of Robert Bunsen (of the Bunsen burner).

Excellent interactive web site for more information about quantum theory http://www.colorado.edu/physics/2000/ Click on “Science Trek” and “Quantum Atom”

Areas of high probability for electrons are orbitals Each orbital can only have 2 electrons What do the orbitals look like?

Different types of spectra Emission spectrum of Sodium

Heisenberg uncertainty principle: you can never know exactly where the electron is if you know how fast it is moving. WERNER HEISENBERG (1901 - 1976