History of Periodic table in Timeline

The periodic table is an organized arrangement of chemical elements into rows (periods) and columns (groups). Representing the periodic law, it displays elements by atomic number, revealing recurring properties. Divided into blocks, elements within the same group share similar chemical characteristics, making it a fundamental tool in chemistry, physics, and other sciences.

1902: Brauner's Asteroid Hypothesis

In 1902, Czech chemist Bohuslav Brauner suggested that all lanthanides could be placed together in one group on the periodic table. He named this the "asteroid hypothesis" as an analogy to the asteroid belt between Mars and Jupiter.

1904: Thomson's Plum-Pudding Model

In 1904, J. J. Thomson proposed the "plum-pudding model" of the atom, which served as the basis for Haas's later calculations of atomic radius. In 1910, Haas used Thomson's plum-pudding model of the atom in calculating the atomic radius of hydrogen

1905: Alfred Werner Proposes Table Similar to Modern Form

In 1905, Swiss chemist Alfred Werner proposed a periodic table form very similar to the modern 32-column form.

1908: Ogawa's Mistaken Discovery of Element 75

In 1908, Japanese chemist Masataka Ogawa found element 75 but mistakenly assigned it as element 43 and named it nipponium. Ogawa's discovery was not recognized until later.

1910: Haas's Estimate of Hydrogen's Atomic Radius

In 1910, physicist Arthur Haas published the first calculated estimate of the atomic radius of hydrogen, coming within an order of magnitude of the accepted value. He used a single-electron configuration based on Thomson's plum-pudding model.

1913: Soddy Coined the Term "Isotope"

In 1913, Frederick Soddy coined the term "isotope" to describe elements with different atomic weights but the same chemical properties. This clarified discrepancies and helped to better understand the composition of elements.

1913: Bohr's Quantum Atom Periodic Table

In 1913, Niels Bohr applied quantization to the atom and produced the first electronic periodic table based on a quantum atom. He theorized that inner electrons were responsible for an element's chemical properties.

1913: Bohr's Electron Shells

In 1913, Niels Bohr explained that the maximum electrons in a shell is eight. His proposed electron configurations for the atoms mostly do not accord with those now known.

1913: Van den Broek's Proposal on Nuclear Charge

In 1913, amateur Dutch physicist Antonius van den Broek proposed that the nuclear charge determines the placement of elements in the periodic table. He illustrated the first electronic periodic table arranging elements by the number of electrons.

1914: Rutherford Confirms van den Broek's View

In 1914, Ernest Rutherford confirmed in his paper that Niels Bohr had accepted Antonius van den Broek's view that nuclear charge determined the placement of elements in the periodic table.

1914: Walther Kossel expands on Bohr's Atomic Theory

In 1914, Walther Kossel systematically expanded and corrected the chemical potentials of Bohr's atomic theory.

1916: Walther Kossel Explains Periodic Table Element Creation

In 1916, Walther Kossel explained that in the periodic table new elements would be created as electrons were added to the outer shell.

1919: Irving Langmuir Postulates Electron Shells

In 1919, Irving Langmuir postulated the existence of "cells" which we now call orbitals, which could each only contain two electrons each, and these were arranged in "equidistant layers" which we now call shells. He made an exception for the first shell to only contain two electrons.

1921: Bury Proposes Stable Electron Configurations

In 1921, Charles Rugeley Bury suggested that eight and eighteen electrons in a shell form stable configurations, also introducing the term 'transition' for elements now known as transition metals.

1922: Bohr Uses Thomsen's Form in Nobel Lecture

In 1922, Bohr used Julius Thomsen's form of the periodic table in his Nobel Lecture.

1923: Pauli Extends Bohr's Scheme

Prompted by Bohr, in 1923 Wolfgang Pauli extended Bohr's scheme to use four quantum numbers, and formulated his exclusion principle.

1925: Hund Arrives at Modern Configurations

In 1925, Friedrich Hund arrived at electron configurations close to the modern ones, shifting periodicity's basis to valence electrons.

1925: Rediscovery of Rhenium

In 1925, Walter Noddack, Ida Tacke, and Otto Berg independently rediscovered element 75 and gave it its present name, rhenium. This corrected Ogawa's earlier mistaken assignment.

1926: Erwin Madelung Empirically Observes the Aufbau Principle

In 1926, the Aufbau principle that describes the electron configurations of the elements was first empirically observed by Erwin Madelung.

1927: Hund Assumes Lanthanide Configuration

In 1927, Hund assumed that all the lanthanide atoms had configuration [Xe]4f5d6s, on account of their prevailing trivalency.

1930: Vladimir Karapetoff Publishes the Aufbau Principle

In 1930, Vladimir Karapetoff was the first to publish the Aufbau principle that describes the electron configurations of the elements.

1936: Pool of Missing Elements Shrinks

By 1936, the pool of missing elements from hydrogen to uranium had shrunk to four: elements 43, 61, 85, and 87 remained missing.

1937: Discovery of Technetium

In 1937, Emilio Segrè and Carlo Perrier discovered technetium, element 43, the first element to be synthesized artificially.

1937: Technetium Synthesized

In 1937, technetium became the first element to be discovered through synthesis rather than in nature. This marked a turning point in expanding the periodic table artificially.

1939: Discovery of Francium

In 1939, French chemist Marguerite Perey discovered francium, element 87, which became the last element to be discovered in nature.

1940: Discovery of Neptunium and Astatine

In 1940, Edwin McMillan and Philip Abelson discovered neptunium, and astatine was produced artificially.

1940: Neptunium Synthesized

In 1940, neptunium was synthesized in the laboratory, marking a significant step in creating elements beyond uranium. This was part of completing the seventh row of the periodic table.

1941: Discovery of Plutonium

In 1941, Glenn T. Seaborg and his team at the Lawrence Berkeley National Laboratory (LBNL) discovered plutonium.

1945: Modern Periodic Table Formed

In 1945, Glenn T. Seaborg discovered that the actinides were f-block elements, leading to a recognizably modern form of the periodic table. This discovery significantly refined the table's structure and improved the understanding of element organization.

1945: Artificial Production of Promethium

In 1945, element 61 (promethium) was produced artificially.

1948: Landau and Lifshitz on Lutetium

In 1948, Lev Landau and Evgeny Lifshitz questioned the grouping of lutetium as an f-block element because the 4f shell is completely filled at ytterbium. This sparked debate about the correct placement of certain elements in the periodic table.

1948: Landau and Lifshitz Suggest Lutetium as d-block Element

In 1948, Soviet physicists Lev Landau and Evgeny Lifshitz noted that lutetium is correctly regarded as a d-block rather than an f-block element.

1955: Synthesis of Elements up to Mendelevium

By 1955, elements up to 101 (mendelevium) were synthesized.

1961: Klechkovsky Derives Part of Madelung Rule

In 1961, Vsevolod Klechkovsky derived the first part of the Madelung rule (that orbitals fill in order of increasing n + ℓ) from the Thomas–Fermi model.

1963: Kondō Suggests Bulk Lanthanum is an f-metal

In 1963, Jun Kondō first suggested that bulk lanthanum is an f-metal, on the grounds of its low-temperature superconductivity.

1963: Kondo on Lanthanum

In 1963, Jun Kondō realized that lanthanum's low-temperature superconductivity implied the activity of its 4f shell. This observation contributed to the ongoing discussion about the proper arrangement of elements in the f-block.

1965: Hamilton's Link Between Superconductivity and Position in the Periodic Table

In 1965, David C. Hamilton linked the superconductivity of lanthanum to its position in the periodic table, arguing that the f-block should consist of elements La–Yb and Ac–No. This was a step towards reevaluating the structure of the f-block.

1971: Demkov and Ostrovsky Derive Complete Madelung Rule

In 1971, Yury N. Demkov and Valentin N. Ostrovsky derived the complete Madelung rule from a similar potential.

1978: IUPAC Systematic Element Names Adopted

In 1978, IUPAC systematic element names, directly relating to atomic numbers, were adopted.

1981: Discoveries of Elements 107-112 at GSI Begin

From 1981, discoveries of elements 107 through 112 at GSI were made possible using cold fusion.

1982: Jensen Brings Attention to f-block Assignment

In 1982, William B. Jensen brought the issue of f-block assignment to wide attention, advocating for the reassignment of lutetium and lawrencium to group 3. This spurred further discussion and research on the topic.

1985: Creation of Transfermium Working Group

In 1985, IUPAC and IUPAP created the Transfermium Working Group (TWG) to set out criteria for element discovery.

1988: IUPAC Reports Support Lutetium and Lawrencium in Group 3

IUPAC reports dating from 1988 supported the reassignment of lutetium and lawrencium to group 3, aligning with the recommendation for 1–18 group numbers. This represented a move towards a more standardized and accurate representation of the periodic table.

1988: Rejection of Helium Placement in Group 2

In 1988, IUPAC rejected a proposal to move helium to Group 2, affirming its placement in Group 18 due to its unreactive nature and full outer shell. This decision was based on its properties matching noble gases more closely than alkaline earth metals.

1988: IUPAC Report Supports Specific Group 3 Composition

In 1988, IUPAC released a report supporting the composition of group 3.

1988: IUPAC Naming System

In 1988, the IUPAC (International Union of Pure and Applied Chemistry) naming system (1–18) for groups in the periodic table was put into use, deprecating the old Roman numeral (I–VIII) system. This change aimed to standardize group nomenclature internationally.

1991: TWG Criteria Published

In 1991, the Transfermium Working Group (TWG)'s criteria for element discovery were published.

1991: Original TWG discovery criteria established

The original discovery criteria set down by the TWG were created in 1991.

1997: Final Names for Elements 102-106

In 1997, elements 102 through 106 received their final names, including seaborgium (106).

1998: Discoveries of Elements 114-118 at JINR Begin

From 1998, the JINR team (in collaboration with American scientists) began discovering elements 114 through 118 using hot fusion.

2002: Oganesson Synthesized

In 2002, oganesson was synthesized, marking the creation of another element in the seventh row of the periodic table. This added to the growing list of artificially produced elements.

2004: Discoveries of Elements 107-112 at GSI End

Until 2004, discoveries of elements 107 through 112 at GSI were made possible using cold fusion.

2010: Completion of the First Seven Rows

By 2010, all 118 elements had been discovered, completing the first seven rows of the periodic table. However, full chemical characterization of the heaviest elements was still pending to confirm their properties matched their predicted positions.

2010: Tennessine Synthesized

In 2010, tennessine was synthesized, completing the elements needed to finish the seventh row of the periodic table. This marked a major achievement in synthetic element creation.

2010: Discoveries of Elements 114-118 at JINR End

Until 2010, the JINR team (in collaboration with American scientists) discovered elements 114 through 118 using hot fusion.

2016: Completion of the Periodic Table's First Seven Rows

By 2016, all elements up to 118 had been officially added to the periodic table, completing its first seven rows.

2016: Naming of Seventh Row Elements

In 2016, the last elements of the seventh row were officially given names, solidifying their place in the periodic table. This included elements like nihonium, moscovium, tennessine, and oganesson.

2018: Attempt to Synthesize Element 119 Begins

Since 2018, an attempt to make element 119 has been ongoing at the Riken research institute in Japan.

2019: International Year of the Periodic Table

In 2019, the United Nations declared the year as the International Year of the Periodic Table.

2020: Updated Discovery Criteria

In 2020, the discovery criteria set down by the TWG were updated.

2021: IUPAC Reports Support Lutetium and Lawrencium in Group 3

IUPAC reports dating from 2021 supported the reassignment of lutetium and lawrencium to group 3. The variation nonetheless still exists because most textbook writers are not aware of the issue.

2021: IUPAC Reaffirms Group 3 Composition Decision

In 2021, IUPAC reaffirmed its decision on the composition of group 3.

2021: IUPAC Report on F-Block Representation

In 2021, an IUPAC report addressed the representation of the f-block, noting that some practitioners support 15-element-wide f-blocks for specialized relativistic quantum mechanics. However, the project's opinion was that such interests should not affect the presentation of the periodic table to the general scientific community.