Timeline of Key Events
1869: Dmitri Mendeleev's First Periodic Table
Dmitri Mendeleev published the first recognizable periodic table, organizing elements by increasing atomic mass and leaving gaps for undiscovered elements.
1894-1898: Discovery of Noble Gases
William Ramsay and Lord Rayleigh discovered noble gases, adding a new group to the periodic table.
1913: Moseley's Atomic Number Concept
Henry Moseley rearranged the periodic table by atomic number rather than atomic mass, resolving inconsistencies in Mendeleev's arrangement.
1940s: Discovery of Transuranium Elements
Seaborg and his team discovered transuranium elements, extending the periodic table and introducing the Actinide series.
The Modern Periodic Table
The modern periodic table organizes elements by increasing atomic number, grouping them into periods and families with similar chemical properties.