When did Dmitri Mendeleev invent the periodic table, ordering the symbols of the chemical elements according to their atomic weights?

The correct answer is 1869.

Key Points

• Dmitri Mendeleev invented the periodic table in 1869, organizing elements based on their atomic weights and properties.
• Mendeleev left gaps in the table for elements yet to be discovered, predicting their properties accurately.
• On March 6, 1869, Mendeleev presented his first periodic table to the Russian Chemical Society.
• Mendeleev’s table demonstrated that when elements are arranged by increasing atomic weight, certain chemical properties repeat periodically.
• This periodic arrangement became the foundation for the modern periodic table used in chemistry today.

Additional Information

• Periodic Law: Mendeleev’s periodic table was based on the periodic law which states that the properties of elements are a periodic function of their atomic weights.
• Modern Periodic Table: Today, the periodic table is organized by atomic number (proton count) rather than atomic weight, as introduced by Henry Moseley in 1913.
• Predicted Elements: Mendeleev accurately predicted the existence and properties of elements like germanium (eka-silicon), gallium (eka-aluminum), and scandium.
• Contributors to Periodicity: Other scientists like John Newlands (law of octaves) and Lothar Meyer worked on periodic classification, but Mendeleev’s table was more comprehensive and widely accepted.
• Significance: Mendeleev’s periodic table provided a systematic framework for studying chemical elements, aiding in the discovery of new elements and advancing the field of chemistry.