Development of the Periodic Table

• Before the discovery of subatomic particles, how did scientists attempt to classify elements and what problems did this cause?


  By arranging them in order of their atomic weight. This meant that some elements were placed in inappropriate groups.
• How did Mendeleev arrange his periodic table and how did he overcome these problems?

  In order of atomic mass, and he solved problems by leaving gaps for undiscovered elements.
• Why was Mendeleev's table accepted?


  He correctly predicted the properties of the elements he left gaps for
• How did the knowledge of isotopes make this possible?


  To explain why the order based on atomic weight was not always correct.