Geos 306, Lecture 2
Introduction, Origin of the Elements, The Nature of the Atom


Origin of the Elements
Element
weight percent
atomic percent
O
29.5
49
Fe
34.6
17
Si
15.2
14
Mg
12.7
14

The Nature of the Atom
12C (6 protons + 6 neutrons),
13C (6 protons + 7 neutrons),
14C (6 protons + 8 neutrons).
One of the isotopes is always the most stable. Isotopes with odd mass numbers are the least stable. That means that 13C is less stable than 12C or 14C.
  • Associated with each proton is an electron. It has 1/2000th the mass of a proton, and an electrical charge that is equal in magnitude but opposite in sign to the charge of a proton.
  • Early models of the atom include the raisin muffin model, Rutherford's model and the Bohr model. The Bohr model led to the concept of quantized energy levels in an atom and wave/particle duality. Currently, the best solution to obtain the location and energies of electrons is provided by the Schrodinger equation.
  • Electrons are the glue that hold atoms together. As such, the nature of electrons and their interactions is the most important concept in chemistry.
  • Review the electronic structure of the atom. It can be described in terms of quantum numbers, with each electron associated with a unique set of quantum numbers. These are:
  • n = principal quantum number, (shell number or row number)
    l = azimuthal quantum number (shape, s = sharp, p= principal, d = diffuse, f = fundamental, etc.)
    m = magnetic quantum number, defines the orientation in a magnetic field, eg px, py, pzetc.
    s = spin quantum number, related to the axial spinning of an electron in the particle concept. We use the up and down arrow symbols.

    Suggested Reading
    1. Wenk and Bulakh: pages 1-11, 580-585
    2. Neese: pages 3-5, 39-46
    3. Broecker, W.S. (1985) How to Build a Habitable Planet. Eldigio Press, Palisades, New York Chapter 1&2
    4. Kirshner, R.P. (1994) The earth's elements. Scientific American, October, pages 59-65 pdf of paper
    5. Klein: pages 42-53
    6. Amaldi, G. The nature of matter, Chicago Press, 1966.