Mendeleev’s Periodic Table

Dmitri Mendeleev (1834–1907), a Russian scientist, developed the Periodic Table of Elements between 1869 and 1872. At that time, 63 elements were known. Mendeleev arranged them in increasing order of atomic masses while also considering their physical and chemical properties.

• He formulated the periodic law, stating: "The properties of elements are periodic functions of their atomic masses."
• Elements with similar properties appeared at regular intervals, forming the basis of the periodic classification.

Structure of Mendeleev’s Periodic Table:

• Vertical columns = Groups.
• Horizontal rows = Periods.
• Mendeleev used the general molecular formulae of hydrides and oxides (e.g., RH₄ for CH₄, RO₂ for CO₂) to classify elements in groups.
• The periodic table was published in 1872 in a German journal.

Mendeleev used the following properties to organise elements:

• Molecular formulae of hydrides and oxides.
• Melting and boiling points.
• Densities of elements and their compounds.

Development of the Periodic Table: Mendeleev prepared separate cards for each element, listing their atomic masses and properties. Arranging these cards led to the invention of the periodic table, which became a major milestone in the classification of elements.