Periodic table of the elements

Arranging elements in order of increasing atomic weight, Mendeleev allowed the length of periods to vary according to the properties of elements, creating a table that predicted undiscovered elements. His periodic table became the foundation for modern chemistry, providing a systematic way to understand element properties and interactions.
 Dmitry Ivanovich Mendeleyev Russia 1869 Periodic table of the elements

Arranging elements in order of increasing atomic weight, Mendeleev allowed the length of periods to vary according to the properties of elements, creating a table that predicted undiscovered elements. His periodic table became the foundation for modern chemistry, providing a systematic way to understand element properties and interactions.