Periodic Properties and the Development of the Periodic Table

  1. The first periodic table was arranged by Dimitri Mendeleev in 1869.
    1. He was a professor of Chemistry. at the University of St. Petersburg in Russia and was confronted with the problem of how to teach about the various elements known at that time. He decided to organized the elements by arranging them into groups that reacted similarly.
    2. He also noticed that various properties would repeat "periodically" so he arranged a table of elements order of atomic mass such that properties would change regularly if you moved across a row while maintaining groups with similar chemical properties in a column.
    3. Go to: http://www.periodic.lanl.gov/mendeleev.htm to see a version of Mendeleev's first table.
  2. Groups with similar properties
    1. All the elements in a group (or column) are called families.
    2. Group 8: The Noble Gases, don't react with other elements.
    3. Group 1: The Alkali Earth Metals, all react with water in the following manner
      2 Li + H2O ---> H2 + 2 LiOH
      2 Na + H2O ---> H2 + 2 NaOH
      ...
      2 Fr + H2O ---> H2 + 2 FrOH
      Using the Periodic Table to Predict Formulas
      Known Formula: Predicted formula:
      B2O3 Aluminum + Oxygen =
      H2O Hydrogen + Sulfur =
      SiO2 Carbon + Oxygen =
      HF Hydrogen + Chlorine =
      Ba(OH)2 Magnesium + Hydroxide =
    4. These are just a few examples of how Mendeleev organized the columns or families.
  3. Periodic Properties
    1. As you move across a row various properties change regularly click on the images below to see a visualization of the various properties. All of these images are from www.webelements.com, one of the best periodic table sites on the web.
      Periodic Trends

      Summary of Trends
  4. Early on the elements were divided into two broad categories -> metals and non-metals. This was done long before anyone knew any detail about the atoms or any of the periodic properties mentioned above.
  5. As you can see what makes something a metal or a non-metal is based on other properties like ionization energy, atomic radius, and electronegativity
  6. When metal atoms are bonded together the electrons become delocalized, jumping from one atom to another. A common analogy is to say that the nuclei of atoms in a metal exist in a "sea of mobile electrons".
  7. This is due to the low ionization energy of these electrons, and is what gives metals the property of conductivity. A typical electric current can be described as electrons moving from one place to another. This can easily happen in metallic substances as depicted below.
  8. Mendeleev organized his table based on properties of density, melting point, and oxide formula. At first people rejected his organization of the elements. However, he found that as he organized the table there seemed to be "holes". He predicted that new elements would be found and he predicted the properties of those new elements. When these new elements were found Mendeleev's periodic table was acclaimed as correct and became and indispensable tool for understanding Chemistry.

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