Periodic Table - Mendeleev Discovery     Lesson 3.2

How did Mendeleev discover the pattern that led to the periodic table?
Dmitri Mendeleev
  • In 1869, the Russian scientist Dmitri Mendeleev discovered a set of patterns in the properties of the elements.
 
 
 










Pattern of Properties
  • He noticed that a pattern of properties appeared when he arranged the elements in order of increasing atomic mass.
 
 
 











Atomic Mass
  • The atomic mass of an element is the average mass of all the isotopes of that element.
 
 
 






Periodic Table & Undiscovered Elements
  • Mendeleev published the first periodic table.
  • In the periodic table, the properties of the elements repeat in each period, or row, of the table.
  • Mendeleev left three blank spaces in the table.
  • He predicted that these spaces would be filled by elements that had not yet been discovered.
 




 
 

Predicting Properties
  • He even predicted the properties of those elements.
  • Those elements were soon discovered. Their properties are close to those predicted by Mendeleev.
 
 
 

Updated Periodic Table
  • The periodic table has been updated since Mendeleev's time as scientists discovered new elements.
 
 
 









Protons & Atomic Number
  • After protons were discovered, elements were rearranged according to atomic number.
  • Some elements changed positions and the patterns of properties became more regular.