Overview
This lecture discusses Dmitri Mendeleev's creation of the periodic table, highlighting his ability to predict unknown elements and their properties, which revolutionized chemistry.
Mendeleev and the Periodic Table
- Dmitri Mendeleev created an early version of the periodic table around 1870.
- The table arranged elements by chemical properties and atomic weights.
- Mendeleev left intentional blank spaces for elements not yet discovered.
Prediction of Unknown Elements
- Mendeleev predicted properties of missing elements based on their table position.
- He named an unknown element “eka-aluminum,” predicting its atomic weight (~68), physical state (solid), and density (6g/cm³).
- Mendeleev accurately described the properties of gallium before it was discovered.
Confirmation of Predictions
- Gallium, discovered by Paul Emile Lecoq de Boisbaudran, matched Mendeleev’s predictions (atomic weight 69.72, density 5.9g/cm³, low melting point).
- Mendeleev similarly predicted scandium, germanium, rhenium, and technetium (eka-manganese).
Legacy and Honors
- Technetium was not isolated until it was synthesized in 1937, decades after Mendeleev’s prediction.
- Mendeleev died in 1907 without a Nobel Prize, but element 101 (mendelevium) was named after him in 1963.
- Only 15 scientists have elements named in their honor, highlighting Mendeleev’s lasting impact.
Key Terms & Definitions
- Periodic Table — A table organizing chemical elements by increasing atomic number and similar properties.
- Eka- — Sanskrit prefix used by Mendeleev to name predicted, undiscovered elements (“eka-aluminum” = one step beyond aluminum).
- Gallium — The element discovered that matched Mendeleev’s prediction of eka-aluminum.
- Technetium — The element predicted as eka-manganese, first synthesized in 1937.
- Mendelevium — Element 101, named to honor Dmitri Mendeleev.
Action Items / Next Steps
- Review the periodic table and note the significance of blank spaces and element predictions.
- Study how property trends allow for the prediction of unknown elements.