Atomic Structure and Periodic Table — Tech Evolutions

Entry	Year	Description	Impact
Mendeleev's Periodic Law to Modern Periodic Law	1913	The original periodic law by Dmitri Mendeleev (1869) stated that properties of elements are periodic functions of their atomic masses. This was revised by Henry Moseley (1913) to the Modern Periodic Law, which states that properties are periodic functions of their atomic numbers, based on his X-ray spectra experiments.	Resolved anomalies in Mendeleev's table (e.g., Ar-K, Co-Ni), provided a more fundamental basis for element classification, and accurately predicted the existence and properties of new elements, leading to the modern periodic table.
Bohr Model to Quantum Mechanical Model	1926	Niels Bohr's model (1913) proposed fixed, circular orbits for electrons. This was superseded by the Quantum Mechanical Model (Schrödinger, 1926), which describes electrons as waves in three-dimensional probability regions called orbitals, defined by quantum numbers.	Provided a more accurate and comprehensive description of atomic structure, explaining complex spectra, chemical bonding, and the behavior of multi-electron atoms, overcoming the limitations of the Bohr model.