Electron Orbitals

							Electron Orbitals

"I think it is safe to say that no one
understands quantum mechanics."
Physicist Richard P. Feynman
Electron Orbitals

   The nature of the nucleus was determined
    using radiation (Rutherford’s gold foil
    experiment)
   The quantum nature of electrons was
    demonstrated by Bohr using spectroscopy.
   Using quantum numbers, electrons are
    defined as occupying orbitals within
    successively larger shells.
   Each orbital can contain 2 electrons of
    opposite spin
Electron Orbitals

 What do electron orbitals look like?
 Although math could be used to
  describe the energy of electrons, what
  they are doing, or what they really are
  was still very unclear.
 Are electrons particles? Waves?
  Both? Something else?
Louis de Broglie (1892-1987)
Electron Orbitals

 Louis de Broglie (1892-1987) was a
  french physicist.
 In 1922, he hypothesized that not only
  electrons, but ALL matter exhibits
  both particle AND wave-like
  properties.
 However, the larger the particle, the
  smaller the wave-like properties
  become.
Electron Orbitals

   The de Broglie hypothesis stated that:
       Any moving particle or object has an
        associated wave.
 This united Einstein’s work on light
  and matter, and created a new branch
  of physics, called wave mechanics.
 Electron can be thought of as
  standing waves. (think skipping
  ropes)
Electron Orbitals
Erwin Schrödinger (1887 – 1961)
Electron Orbitals

 In 1926, Erwin Schrödinger discovered
  a set of equations that described the
  structure of orbitals.
 His math was based on Louis de
  Broglie’s concept of electrons as
  waves.
 This was the one of the earliest
  formulations of Quantum mechanics.
 Electron Orbitals

 Schrödinger’s equations defined the
  most probable position of an electron
  in an atom.
 An orbital is defined as the area within
  which the electron will most likely be
  found.
 Orbitals are not uniform; within all
  orbitals, there are different probabilities
  of where the electron will be.
          Electron Orbitals




                                      probability
 Hydrogen
  nucleus


The hydrogen atom has one
electron in a 1s orbital. As the
distance from the nucleus                           0.05      0.15
increases, the probability of the
                                                     Distance from
electron occurring at that point                     nucleus in nm
first increases, then diminishes to
the point of virtual nothingness
           Electron Orbitals




                         probability
However, we
must think in
3D. The
probability of
finding the                            0.05      0.15
electron is the
                                        Distance from
same no                                 nucleus in nm
matter which
direction we
choose
Electron Orbitals

 Electron orbitals can be thought of as
  an electron cloud.
 This cloud is a probability map of where
  electrons are most likely to be found
  around the nucleus.
 The opacity of the cloud is proportional
  to the probability density.
Electron Orbitals

 Orbitals can thus be viewed as a 3D
  electron probability density map that
  outlines the area the electron is
  probably found.
 The shape of an orbital is determined
  by the 2o quantum number, l.
 The orientation is determined by the
  magnetic number, ml.
1s (l = 0, ml = 0)
              z

                     y




                     x
2s (l = 0, ml = 0)
               z

                     y




                     x
2p (l = 1, ml = 0)
              z

                     y




                     x
2p (l = 1, ml = -1)
              z

                      y




                      x
2p (l = 1, ml = +1)
              z

                      y




                      x
Werner Heisenberg
Quantum Mechanics

 Simultaneously, Werner Heisenberg
  also developed a set of equations that
  explained the behaviour of electrons.
 This was called matrix mechanics.
 However, the math was so
  complicated, that Heisenberg himself
  did not fully understand why it
  explained the quantum nature of
  electrons.
Quantum Mechanics

 Heisenberg and Schrödinger’s
  discoveries gave birth to quantum
  mechanics.
 Quantum mechanics explains (and
  makes predictions!) about the natural
  laws that govern at the molecular
  level.
Quantum Mechanics

 One of the consequences of quantum
  mechanics is that it is not possible to
  simultaneously know the position and
  momentum (speed and direction) of a
  particle.
 This was determined by Heisenberg,
  and is hence called the Heisenberg
  Uncertainty Principle.
Quantum Mechanics

   Essentially, the Uncertainty Principle exists
    because to determine the property of a
    particle, one must interact with it.
   This interaction with the particle will alter the
    properties of the particle.
   At the atomic level, the interactions between
    particles becomes very significant.
   Thus, the smaller the system to be
    observed, the greater the effect of the
    Uncertainty Principle
Review Questions

 Page 219
 #1-11 (true/false)

 #12-19 (multiple choice)

 Pg 220

 #4-6, 9-17 (short answer)