Which of the following statements is/are correct regarding Döbereiner’s Triads?

I. Döbereiner showed that when the three elements in a triad were written in the order of increasing atomic masses; the atomic mass of the middle element was roughly the average of the atomic masses of the other two elements.

II. Döbereiner identified eight triads from the elements known at that time. 

The correct answer is Only I.

Key Points

• Döbereiner's triads were an early attempt to classify elements based on their properties and atomic masses.
• He proposed that groups of three elements (triads) could be formed where the atomic mass of the middle element is approximately the average of the atomic masses of the other two elements.
• One example of such a triad is lithium (Li), sodium (Na), and potassium (K), where the atomic mass of sodium is roughly the average of lithium and potassium.
• This observation was significant in the development of the periodic table, providing insight into the relationship between atomic mass and chemical properties.
• Döbereiner identified only a few triads, not eight, due to the limited number of elements known at the time.

Additional Information

• Periodic Table Development:
  • The periodic table has evolved over time with contributions from various scientists, including Döbereiner, Newlands, Mendeleev, and Moseley.
  • Mendeleev’s periodic table arranged elements based on atomic masses and properties, predicting the existence of undiscovered elements.
  • Modern periodic tables are arranged by atomic number, following Moseley’s discovery that atomic number is more fundamental than atomic mass.
• Law of Triads:
  • Proposed by Johann Wolfgang Döbereiner in 1817.
  • It was one of the earliest attempts to classify elements by their properties.
  • Although only a few triads were identified, it paved the way for future developments in periodic classification.
• Examples of Döbereiner’s Triads:
  • Calcium (Ca), Strontium (Sr), Barium (Ba)
  • Chlorine (Cl), Bromine (Br), Iodine (I)
  • Sulfur (S), Selenium (Se), Tellurium (Te)
• Limitations of Triads:
  • Not all known elements could be grouped into triads.
  • Some elements did not fit the average mass rule accurately.
  • Limited by the number of elements discovered at the time.