Development of the periodic table

• How many elements had been discovered by the 19th century?

  Over 50 elements
• What was the main goal of early attempts to arrange the periodic table?

  To reflect the similarities in chemical properties of elements
• What was the arrangement method used in early periodic tables?

  • Arranged strictly by atomic weight
  • Protons, neutrons, and electrons were not yet discovered
• Who proposed the 'law of octaves' and in what year?

  John Newland in 1864
• What did Newland notice about the elements when he arranged them by atomic mass?

  Every 8th element had similar chemical properties
• What was a major criticism of Newland's law of octaves?

  Many new elements did not fit into the table
• What was the main focus of Mendeleev's periodic table?

  Arranging elements based on similarities of chemical and physical properties
• In what year did Mendeleev categorize the elements into his 'Periodic System'?

  1869
• What did Mendeleev do to accommodate undiscovered elements in his periodic table?

  He left gaps for them to be filled in later
• How did Mendeleev rearrange elements that did not fit the pattern of increasing atomic mass?

  He placed them in groups with similar properties
• Which two elements did Mendeleev swap positions in his periodic table?

  Iodine and Tellurium
• What is the current explanation for the order of Iodine and Tellurium in the periodic table?

  It is due to the existence of isotopes
• What is the purpose of the periodic table?

  To organize and understand the properties of different elements
• Who developed the periodic table and when was it first published?

  Dmitri Mendeleev in 1869
• How did Mendeleev develop the periodic table?

  By organizing elements based on atomic mass and chemical properties
• What are the key features of the periodic table?

  Arrangement of elements by increasing atomic number and properties
• How has the periodic table changed since Mendeleev's time?

  New elements have been discovered and properties studied
• What are the main topics covered in the development of the periodic table?

  • The Early Periodic Table
  • Newlands Octaves
  • Mendeleev’s Periodic Table
  • Rearranging the Position of Elements
• How did Mendeleev arrange elements in his periodic table?


  In order of increasing atomic weight
• Why did Mendeleev switch elements in his periodic table?


  Mendeleev would switch the order of specific elements so they fitted the patterns of other elements in the same group
• Why did Mendeleev leave gaps in his periodic table?


  Mendeleev left gaps in his periodic table to account for elements that had not yet been discovered but were predicted to exist based on his understanding of the periodic trends.
• Why did scientists accept Mendeleev’s periodic table?


  He lefts gaps for undiscovered elements which were discovered years later
• In the modern periodic table how are elements arranged?


  By increasing atomic number.
• What is the issue of ordering the periodic table by increasing atomic weight?


  Elements can appear in the wrong order due to the presence of isotopes