Why did Mendeleev reverse the order of the tellurium (Te) and iodine (I) elements?
Answer (2)
Mendeleev reversed the order of tellurium and iodine in his periodic table to prioritize chemical properties over atomic weights. He observed that iodine's properties were more aligned with halogens than with the metalloid tellurium. This decision reflected his understanding of periodicity, which groups elements with similar characteristics together, even if it meant deviating from strict atomic weight order.
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Dmitri Mendeleev, a Russian chemist, is well-known for developing one of the first periodic tables of elements in 1869. He arranged the elements in order of increasing atomic weight while grouping elements with similar properties together.
However, when Mendeleev encountered the elements Tellurium (Te) and Iodine (I), he found that Tellurium had a higher atomic weight than Iodine, yet placing Tellurium before Iodine maintained the periodicity and properties more accurately. Thus, he reversed the order of these two elements.
At that time, the explanation for this reversal was not clear because the concepts of atomic number and electron configuration were not yet developed. These concepts, which came later with advancements in atomic theory, revealed that the atomic number (the number of protons in an atom's nucleus) is the proper basis for ordering the elements.
Despite this initial anomaly, Mendeleev's intuition was correct in prioritizing chemical properties and periodic trends over atomic weights. This decision highlighted the periodic law, which states that the properties of elements are a periodic function of their atomic numbers.
Therefore, Mendeleev reversed the order of Tellurium and Iodine based on their chemical properties rather than atomic weight, showcasing the predictive power and accuracy of his periodic table. This work laid the foundation for the modern understanding and organization of elements in the periodic table, where the elements are listed in order of increasing atomic number.
