1. Atomic Mass: Mendeleev arranged the elements in ascending order of their atomic masses. He observed that elements with similar chemical properties tended to have similar atomic masses. For example, elements in the same group (vertical column) had similar chemical properties and were arranged sequentially based on their increasing atomic masses.
2. Chemical Properties: Mendeleev emphasized the importance of chemical properties in organizing the elements. He grouped elements with similar chemical behavior together, even if their atomic masses were not in perfect numerical order. For instance, iodine was placed in the same group as fluorine, chlorine, and bromine, despite having a higher atomic mass than tellurium.
3. Periodic Trends: Mendeleev noticed periodic trends in the properties of the elements. He observed that certain physical and chemical properties repeated themselves at regular intervals when elements were arranged in the order of increasing atomic masses. This led to the concept of periodicity, which is a fundamental principle of the periodic table.
4. Gaps and Predictions: Mendeleev left gaps in his periodic table for undiscovered elements. He predicted the existence and properties of these missing elements based on the patterns and trends he observed among the known elements. For example, he predicted the existence of elements such as gallium, scandium, and germanium, which were later discovered and confirmed.
5. Mendeleev's Periodic Law: Mendeleev's work led to the formulation of the periodic law, which states that "the properties of the elements are periodic functions of their atomic masses." This law became the guiding principle for organizing and understanding the chemical elements and their behavior.
Mendeleev's periodic table was revolutionary at the time and provided a systematic framework for classifying and studying the chemical elements. It not only organized known elements but also predicted the existence of new ones, leading to further advancements in the field of chemistry.
