Final Answer:
The periodic table was developed by Mendeleev in the 1800s. He arranged the elements that were known at the time by increasing atomic mass and placed them into groups based on similar properties.
Step-by-step explanation:
Dmitri Mendeleev's groundbreaking work on the periodic table in the late 19th century laid the foundation for our modern understanding of chemical elements. In his arrangement, Mendeleev ordered the elements by increasing atomic mass.
Atomic mass refers to the mass of an atom, expressed in atomic mass units (u), which accounts for the sum of protons and neutrons in an atom's nucleus. Mendeleev's insight was that by organizing elements by their atomic masses, a pattern emerged in which elements with similar properties fell into vertical columns, or groups.
The significance of this arrangement became evident as it allowed Mendeleev to predict the properties of yet-to-be-discovered elements. Gaps in his table suggested the existence of elements not yet known, and he could predict their properties based on the trends observed in neighboring elements. For instance, he predicted the properties of germanium, gallium, and scandium before their actual discovery, showcasing the predictive power of his periodic table.
However, later advancements in atomic theory and the development of the modern periodic table refined Mendeleev's approach. Today, the elements are arranged by increasing atomic number, which corresponds to the number of protons in an atom.
Despite this modification, Mendeleev's pioneering work remains a cornerstone in the history of chemistry, providing a systematic framework that paved the way for a deeper understanding of the relationships between different elements.