1913 ⟶ Atomic Number Defined

Henry Moseley: defined atomic number
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Year
1911
1913

⚛️ van den Broek Proposes Organization by Atomic Number

Antonius van den Broek proposes the idea that the elements on the periodic table are more properly organized by positive nuclear charge rather than atomic weight.⟶
van den Broek Proposes Organization by Atomic Number (1911)
ChemistryPeriodic TableAtomic Numbervan den BroekElements
NetherlandsNetherlands

☢️ Rutherford: Discovery of the Atomic Nucleus (Rutherford Model)

Ernest Rutherford: Discovery of the atomic nucleus (Rutherford model)⟶
Rutherford: Discovery of the Atomic Nucleus (Rutherford Model) (1911)
PhysicsAtomic PhysicsRutherfordNuclear ModelAtom
United KingdomUnited Kingdom

🔢 Atomic Number Defined

Henry Moseley: defined atomic number⟶
Atomic Number Defined (1913)
Atomic NumberMoseleyPeriodic TableAtomic PhysicsChemistryEarly 20th Century Chemistry
United KingdomUnited Kingdom

🔢 Atomic Number Concept Introduced

Henry Moseley, working from Van den Broek's earlier idea, introduces concept of atomic number to fix inadequacies of Mendeleev's periodic table, which had been based on atomic weight.⟶
Atomic Number Concept Introduced (1913)
Atomic NumberPeriodic TableHenry MoseleyAtomic PhysicsChemistryPeriodic LawEarly 20th Century Chemistry
United KingdomUnited Kingdom

⚛️ Concept of Isotopes Proposed

Frederick Soddy proposes the concept of isotopes, that elements with the same chemical properties may have differing atomic weights.⟶
Concept of Isotopes Proposed (1913)
IsotopesRadioactivityFrederick SoddyNuclear ChemistryAtomic PhysicsEarly 20th Century Chemistry
United KingdomUnited Kingdom