Dimitri Mendeleve

• Triads


  Groups of three elements with chemical similarities
• In triads, the atomic weight of the second element was almost exactly the average of the atomic weights of the first and third element
• Law of octaves


  Newlands' relationship between the chemical properties of elements and their atomic masses, where the eighth element has similar properties to the first
• Newlands tried to force all the known elements to fit into his octaves, but many of the heavier elements discovered later did not fit into his patterns
• Dmitri Mendeleev


  First scientist to make a periodic table much like the one we use today
• Mendeleev's periodic table


  1. Listed elements in order of increasing atomic weight

  2. Placed elements with similar chemical behavior underneath each other
• Similarities between lithium and sodium

  • Shiny metal
  • Soft enough to be cut with a spoon
  • Reacts readily with oxygen
  • Reacts violently with water
  • Produces hydrogen gas and metal hydroxide
• Mendeleev occasionally broke the trend of listing elements by increasing atomic weight in order to group elements with the same chemical behavior together
• Mendeleev left holes in his table for undiscovered elements and predicted their properties
• Modern periodic table


  • Includes noble gases
  • Organized by atomic number rather than atomic mass
  • Vertical columns are groups/families of elements with similar electron configurations
• Moseley's research showed there were gaps in the periodic table at atomic numbers 43 and 61, which are now known to be Technetium and Promethium
• Mendeleev did not know about electron configuration, he placed elements based on their chemical behavior