Understanding Mendeleev’s Periodic Table Basis

Dmitri Mendeleev is credited with developing one of the earliest functional periodic tables. His work was groundbreaking in organizing the known chemical elements and predicting the properties of undiscovered ones. The fundamental principle he used to arrange the elements is key to understanding his periodic table.

Mendeleev formulated a periodic law which states that the properties of elements are a periodic function of their atomic masses. This means that when elements are arranged in increasing order of their atomic masses, their properties repeat after certain regular intervals.

Let's look at the options provided in the question regarding what Mendeleev considered the periodic function of element properties:

• Atomic number: The concept of atomic number, which is the number of protons in an atom's nucleus, was not known at the time Mendeleev developed his periodic table. The modern periodic law is based on atomic number, but Mendeleev used a different property.
• Atomic mass: Mendeleev primarily arranged elements in his periodic table in increasing order of their atomic mass. He observed that elements with similar properties appeared at regular intervals when ordered this way. Therefore, he concluded that the properties were a periodic function of their atomic mass.
• Ionization enthalpy: Ionization enthalpy is an important property of elements and does show periodicity in the modern periodic table. However, it was not the fundamental property used by Mendeleev to arrange the elements and define his periodic law.
• Atomic size: Atomic size (or atomic radius) is another property of elements that exhibits periodicity. Like ionization enthalpy, it is a periodic property but was not the basis for the arrangement of elements in Mendeleev's periodic table.

Mendeleev's genius lay in using atomic mass to predict properties and even leave gaps for elements not yet discovered, accurately predicting their properties based on the position in his atomic mass-based table.

Therefore, in Mendeleev’s periodic table, the properties of the elements are considered a periodic function of their atomic mass.

Revision Table: Key Concepts on Mendeleev's Table

• Mendeleev arranged elements based on increasing atomic mass.
• He stated that properties repeat periodically when elements are arranged by atomic mass.
• His table allowed prediction of properties for undiscovered elements.

Additional Information: Evolution of Periodic Table

While Mendeleev's periodic table based on atomic mass was a significant achievement, it had some limitations (e.g., isotopes, position of certain elements). The discovery of atomic number and Henry Moseley's work led to the modern periodic law, where elements are arranged based on atomic number, providing a more consistent and accurate periodic classification of elements.

Understanding the basis of Mendeleev's table on atomic mass is crucial for appreciating the development of the periodic table as we know it today.