In which order did Mendeleev arrange the elements in his periodic table?

The correct answer is Increasing atomic mass.

Key Points

• Dmitri Mendeleev arranged the elements in his periodic table based on their increasing atomic mass.
• He grouped elements with similar chemical properties into vertical columns called groups.
• Mendeleev left gaps in his periodic table to predict the existence of undiscovered elements and their properties.
• The periodic table was published in 1869, marking a significant advancement in the study of chemistry.
• Although atomic mass was the primary criterion, Mendeleev occasionally altered the arrangement to ensure elements with similar properties were aligned correctly.

Additional Information

• Periodic Table:
  • A tabular arrangement of chemical elements organized by their atomic number, electron configuration, and recurring chemical properties.
  • The modern periodic table is based on the Moseley’s concept of increasing atomic number, rather than atomic mass.
• Atomic Mass:
  • The total mass of protons and neutrons in an atom's nucleus.
  • Mendeleev used atomic mass as a criterion because atomic numbers were unknown at the time.
• Predictions Made by Mendeleev:
  • Mendeleev successfully predicted the properties of elements like gallium (eka-aluminum) and germanium (eka-silicon).
  • These predictions were later confirmed with the discovery of these elements.
• Limitations of Mendeleev’s Table:
  • Some elements were placed out of order based on atomic mass to align with chemical properties.
  • The periodic table did not account for the existence of isotopes, which have the same atomic number but different atomic masses.