Periodic Table Timelines

Periodic Table Timelines:

A chronology of the events that have resulted in our present periodic table of the elements and
a celebration of the 150th anniversary of the Mendeleev (birthday, 02/08/1834) periodic table (1869).

(Note: A Powerpoint presentation of the historical developments that have culminated in our current periodic table is available at:
http://murov.info/timeline.pptx ). This slide presentation contains images but minimal narrative which needs to be provided by the presenter.)
One example of a YouTube presentation on the development of the periodic table is available at: https://www.youtube.com/watch?v=I5H1SeepnaU

A web site containing many of the important milestones in organic chemistry is available (6/10/18) at: http://murov.info/organicmilestones.htm

https://cen.acs.org/articles/96/i1/Periodic-table-turns-150-2019.html
https://en.unesco.org/news/2019-proclaimed-international-year-periodic-table-chemical-elements
https://iupac.org/united-nations-proclaims-international-year-periodic-table-chemical-elements/
Also see: http://www.chem.unt.edu/~jimm/REDISCOVERY%207-09-2018/

CONTENTS

Chronology for the development and discovery of the periodic table, atomic structure, electronic theory and the elements.

Three thead timeline for the development of the periodic table, atomic structure and electronic theory.

Medium-long forms of the periodic table with element colors.

Selected periodic properties of the elements (ionization energy, atomic radius, valence).

Some periodic table questions and unresolved issues.

Chronology for the development and discovery of the periodic table, atomic structure, electronic theory and the elements.

Image¹	contributor	contribution		year		element²		Location	#³	At. #

				>9000 BC		Copper		Mid-East	1	29
				7000 BC		Lead		Egypt	2	82
				>6000 BC		Gold		Egypt	3	79
				>5000 BC		Silver		Greece	4	47
				>5000 BC		Iron		Egypt	5	26
				3750 BC		Carbon		Egypt	6	6
				3500 BC		Tin		Egypt	7	50
				>2000 BC		Sulfur		China	8	16
				>2000 BC		Mercury		China	9	80
				>1600 BC		Antimony			10	51
				>1000 BC		Zinc		India	11	30
	Empedocles	Proposed 4 element concept – everything derivable from earth, air, fire and water.		450 BC				Greece
	Democritus, Leucippus	Based on reason, as contrasted with experiment, proposed that there is a limit to the subdivision of matter that culminates in an indivisible particle called atomos.		440 BC				Greece
	Plato, Aristotle	Added a fifth element, "aether", promoted concept of continuity of matter and rejected concept of atoms. As a result, atoms were not generally accepted as reality for the next 2000 years.		340 BC				Greece
				300		Arsenic		Egypt	12	33
	Jabir ibn Hayyan	Experimentalist and alchemist recognized by some as father of chemistry. He developed classifications of metals and non-metals.		800				Iran, Iraq
	Robert Boyle	Considered by many as the first modern chemist. Author of Sceptical Chymist.		1661				Ireland, England
	Hennig Brand			1669		Phosphorus		Germany	13	15
	Georg Ernst Stahl	Stahl promoted the concept of phlogiston first proposed by his mentor, Johann Joachim Becher, and then expanded by Stahl’s student, J. H. Pott but debunked years later by Lavoisier and others.		1703				Germany
	George Brandt			1735		Cobalt		Sweden	14	27
	A. de Ulloa			1735		Platinum		Columbia	15	78
	A. Cronstedt			1751		Nickel		Sweden	16	28
	C. Younger			1753		Bismuth		France	17	83
	Joseph Black			1755		Magnesium		Scotland	18	12
	H. Cavendish			1766		Hydrogen		England	19	1
	Carl Scheele, Joseph Priestley			1772		Oxygen		Sweden England	20	8
	D. Rutherford			1772		Nitrogen		Scotland	21	7
	Carl Scheele			1774		Chlorine		Sweden	22	17
	Johan G. Gahn			1774		Manganese		Sweden	23	25
	Antoine Lavoisier	Considered to be founder of modern chemistry, demonstrated conservation of mass in chemical reactions within measureable limits, dealt phlogiston concept a blow and attempted to organize matter by properties. Provided empirical evidence for elements as contrasted to earlier abstract concept. http://www.meta-synthesis.com/webbook/35_pt/pt_database.php?PT_id=3		1778				France
	Carl Scheele			1778		Molybdenum		Sweden	24	42
	J. & F. Elhuyar			1783		Tungsten		Spain	25	74
	F. Reichenstein			1783		Tellurium		Romania	26	52
	M. H. Klaproth			1789		Zirconium		Germany	27	40
	M. H. Klaproth			1789		Uranium		Germany	28	92
	A. Crawford, W. Cruickshank			1790		Strontium		Scotland	29	38
	William Gregor			1791		Titanium		England	30	22
	Johann Gadolin			1794		Yttrium		Finland	31	39
	Jeremias B. Richter	Suggested that chemical reactions have a mathematical relationship that he called stoichiometry and proposed law of definite proportions.		1794				Germany
	Joseph Proust	Responsible for law of constant composition.		1794				France
	L-N. Vauquelin			1797		Chromium		France	32	24
	L-N. Vauquelin			1798		Beryllium		France	33	4
	A. M. Del Rio			1801		Vanadium		Spain	34	23
	C. Hatchett			1801		Niobium		England	35	41
	A. G. Ekenberg			1802		Tantalum		Sweden	36	73
	W. Wollaston			1803		Palladium		England	37	46
	J. J. Berzelius, W. v. Hisinger, M. H. Klaproth			1803		Cerium		Sweden Germany	38	58
	S. Tennant			1803		Osmium		England	39	76
	S. Tennant			1803		Iridium		England	40	77
	W. H. Wollaston			1803		Rhodium		England	41	45
	John Dalton	Revived, utilizing experimental evidence and work of Richter and Proust, the concept of atomos with the Dalton atomic theory. Proposed law of multiple proportions and developed ranking of atomic masses (actually equivalent masses).		1803				England
	Joseph Louis Gay-Lussac, Alexander von Humboldt, H. Cavendish	Gases at constant T and P combine in simple numerical proportions by volume, and the resulting product gases also bear a simple proportion by volume to the volumes of the reactants.		1808				France
	Sir H. Davy			1807		Potassium		England	42	19
	Sir H. Davy			1807		Sodium		England	43	11
	Sir H. Davy			1808		Calcium		England	44	20
	L. Gay-Lussac, L-J. Thénard, Sir H. Davy			1808		Boron		France, England	45	5
	Sir H. Davy			1808		Barium		England	46	56
	Barnard Courtois			1811		Iodine		France	47	53
	Amedeo Avogadro	Developed law that equal volumes of different gases contain the same number of molecules and the diatomic nature of many gases which many years later enabled chemists (~1860) to distinguish between equivalent and atomic masses.		1811				Italy
	William Prout	Proposed concept that atomic weights of elements are whole-number multiples of the atomic weight of hydrogen suggesting that all elements are composed of hydrogen atoms.		1815				England
	J. A. Arfvedson			1817		Lithium		Sweden	48	3
	J. J. Berzelius			1817		Selenium		Sweden	49	34
	F. Stromeyer			1817		Cadmium		Germany	50	48
	J. J. Berzelius			1824		Silicon		Sweden	51	14
	H. C. Oersted			1825		Aluminum		Denmark	52	13
	Antoine Balard			1826		Bromine		France	53	35
	Jöns Jacob. Berzelius	In addition to discovering elements, Berzelius published list of atomic weights (later vastly improved by Cannizzaro - 1860) and developed element symbols.		1828	Thorium		Sweden		54	90
	Johann W. Döbereiner	Demonstrated concept of triads, groups of elements (later realized to be in the same group) in which the mass of the middle element was close to the average of the masses of the first and third element.		1829			Germany
	C. Mosander			1839	Lanthanum		Sweden		55	57
	Leopold Gmelin	Using the concept of triads, developed a table of 55 elements in a periodic system that contained many of the important relationships of our modern periodic table. https://www.meta-synthesis.com/webbook/35_pt/pt_database.php?PT_id=268		1843			Germany
	C. Mosander			1843	Erbium		Sweden		56	68
	C. Mosander			1843	Terbium		Sweden		57	65
	Karl K. Klaus			1844	Ruthenium		Russia		58	44
	Peter Kremers	Extended the concept of triads from vertical to both vertical and horizontal relationships.		1856			Germany
	R. W. Bunsen, G. R. Kirchhof			1860	Cesium		Germany		59	55
	Stanislao Cannizzaro	Played important role in establishing useful table of atomic masses that enabled development within a decade of several periodic tables.		1860			Italy
	R. W. Bunsen, G. R. Kirchhof			1861	Rubidium		Germany		60	37
	W. Crookes			1861	Thallium		England		61	81
	Alexandre-Émile Béguyer de Chancourtois	Ordered elements according to increasing atomic mass in a chart that demonstrated periodic properties of the elements. https://www.meta-synthesis.com/webbook/35_pt/pt_database.php?PT_id=7		1862			France
	F. Reich, H. T. Richter			1863	Indium		Germany		62	49
	John Newlands	Ordered elements according to increasing atomic mass in a chart that demonstrated periodic properties of the elements and added rule of octaves. https://www.meta-synthesis.com/webbook/35_pt/pt_database.php?PT_id=8		1864			England
	William Odling	Ordered elements according to increasing atomic mass in a chart that demonstrated periodic properties of the elements. https://www.meta-synthesis.com/webbook/35_pt/pt_database.php?PT_id=91		1864			England
	Gustavus Hinrichs	Ordered elements according to increasing atomic mass in a spiral chart that demonstrated periodic properties of the elements. Used spectral evidence. https://www.meta-synthesis.com/webbook/35_pt/pt_database.php?PT_id=270		1867			Denmark, U.S.
	Jules Janssen			1868	Helium		France		63	2
	Dimitri Mendeleev	Shares with Meyer recognition for predecessor of modern periodic table with elements ordered by atomic mass and groups determined by chemical properties. Te and I placed correctly despite inverted masses. https://www.meta-synthesis.com/webbook/35_pt/pt_database.php?PT_id=9		1868, 1869			Russia
	Lothar Meyer	Shares with Mendeleev recognition for predecessor of modern periodic table with elements ordered by atomic mass and groups determined by chemical properties. https://www.meta-synthesis.com/webbook/35_pt/pt_database.php?PT_id=12		1868, 1870			Germany
	P. Boisbaudran			1875	Gallium		France		64	31
	J. C. G. Marignac			1878	Ytterbium		Switzerland		65	70
	Per T. Cleve			1878	Holmium		Sweden		66	67
	Lars F. Nilson			1879	Scandium		Sweden		67	21
	Per T. Cleve			1879	Thulium		Sweden		68	69
	P. Boisbaudran			1879	Samarium		France		69	62
	J. C. G. Marignac			1880	Gadolinium		Switzerland		70	64
	C. F. A. Welsbach			1885	Praseodymium		Germany		71	59
	C. F. A. Welsbach			1885	Neodymium		Austria		72	60
	C. Winkler			1886	Germanium		Germany		73	32
	P. Boisbaudran			1886	Dysprosium		France		74	66
	Henri Moissan			1886	Fluorine		France		75	9
	William Crookes	Developed Crookes tube (1975) enabling discovery of electron and also suggested atomic weights are an average of different kinds of atoms of the same element (concept of isotopes).		1886			England
	Eugen Goldstein	Discovered rays that were eventually realized to be hydrogen nuclei or protons.		1886			Germany
	W. Ramsay, Lord Rayleigh			1894	Argon		England, Scotland		76	18
	W. Röntgen	Discovered X-rays.		1895			Germany
	H. Becquerel	Discovered radioactivity that enabled Marie Curie and others to isolate radioactive elements that filled in gaps in periodic table and for Rutherford to design gold foil expt.		1896			France
				1896	Europium		France		77	63
	J. J. Thomson	Discovered electron using Crookes’ tube and demonstrated that this tiny negatively charged particle had a huge charge to mass ratio (e/m) and was present in atoms of all elements. Also found evidence for protons. In 1904, he proposed “plum pudding” model for atom that was disproved by Rutherford in 1911.		1897
	W. Ramsay, M. M. Travers			1898	Krypton		Scotland		78	36
	W. Ramsay, M. M. Travers			1898	Neon		Scotland		79	10
	W. Ramsay, M. M. Travers			1898	Xenon		Scotland		80	54
	Marie Curie, Pierre Curie	With her husband Pierre, discovered polonium and later other radioactive elements.		1898	Polonium		France		81	84
	M. & P. Curie			1898	Radium		France		82	88
	A-L. Debierne			1899	Actinium		France		83	89
	F. E. Dorn			1900	Radon		Germany		84	86
	Max Planck	Began modern era of quantum mechanics when he showed that energy did not flow in a steady continuum, but was delivered in discrete packets called quanta with E = hn.		1900			Germany
	William Ramsay		Discovery of inert gases in late 1890’s (helium observed in sun in 1868 but isolated by William Ramsay and Raleigh in 1895) by Ramsay and co-workers led Ramsay, Mendeleev and others to add inert gases to periodic table. See: https://www.meta-synthesis.com/webbook/35_pt/pt_database.php?Button=All	1902			Scotland
	Hantaro Nagaoka		Proposed solar system like model of the atom but not accepted until gold foil experiment of Rutherford in 1911.	1904			Japan
	Richard Abegg		Developed concept of valence and explained inertness of noble gases based on octave of electrons in outer shell	1904			Germany
	Alfred Werner		Presented periodic table with substantial resemblance to most popular form used today. https://www.meta-synthesis.com/webbook/35_pt/pt_database.php?PT_id=64	1905			Switzerland
	Albert Einstein		Light which had been considered a form of electromagnetic waves, must also be thought of as particle-like. Theories of relativity also are important considerations in electron orbitals of high atomic number.	1905			Germany
	G. Urbain, C. F. A. Welsbach Charles James			1907	Lutetium		France, Austria, U.S.		85	71
	Jean Baptiste Perrin		Strongly supported atomic theory, laid groundwork for Thomson’s discovery of the electron and proposed solar system model for atom (not accepted until 1911).	1907			France
	Antonius Johannes van den Broek		First to change ordering of elements from atomic mass to charge in the nucleus (later called atomic number).	1907			Netherlands
	Robert Millikan		Oil drop experiment determined charge on electron and enabled calculation of mass of electron from Thomson’s e/m ratio.	1909			United States
	Ernest Rutherford		Performed gold foil experiment that demonstrated nuclear model for atom with tiny nucleus but with almost all the mass of the atom. Before gold foil experiment, he showed that alpha particles are helium nucleii. Also, often given credit for discovery of proton (however, see Goldstein in 1886)	1911			England (born in New Zealand)
	Frederick Soddy		Worked with Rutherford and elevated Crooke’s suggestion of isotopes into a theory. In 1913, Hevesy and Paneth provided evidence that isotopes chemically behave the same.	1912			England
	Henry Moseley		Using X-rays, demonstrated that the number of protons (atomic number) as suggested by van den Broek instead of atomic mass is the correct basis for the ordering of the elements.	1913			England
	Niels Bohr		Applied quantum theory to atoms. Using a planetary model, derived a correct mathematical description of electron in hydrogen but model failed for multiple electron atoms. Proposed Aufbau Principle. Attempted to use electron structure to explain shape of periodic table. Produced symmetrical periodic table that improved tables of T. Bayley and J. Thomsen and was improved again by E. Scerri in 1997. https://www.meta-synthesis.com/webbook/35_pt/pt_database.php?PT_id=19	1913, 1922			Denmark
	K. Fajans, Otto Göhring			1913	Protactinium		Germany		86	91
	Gilbert Lewis		Developed concept of electron pairs, bonding and Lewis structures for atoms and molecules. Expanded work on valence concepts of Richard Abegg.	1916			U.S. (CA)
	I. Langmuir, C. Bury, J. M. Smith		Arranged elements according to electron arrangement.	1919, 1921, 1924			U.S., England
	Francis Aston		Invented mass spectrometer and using it, was the first to experimentally demonstrate existence of isotopes of many elements.	1922			England
	G. C. Hevesy, Dirk Coster			1923	Hafnium		Denmark		87	72
	Edmund Stoner		Improved Bohr’s attempt to correlate periodic table with electron theory by adding a third quantum number.	1924			England
	Louis-Victor de Broglie		Predicted wave nature of electrons and all matter.	1924			France
	Wolfgang Pauli		Added spin quantum number to make 4 quantum numbers that enable strong correlation of electron orbital theory to experimental properties and shape of periodic table. Introduced Pauli Exclusion Principle.	1924			Switzerland
	Werner Heisenberg		Used matrix mechanics to mathematically describe electron orbitals. His results were later shown to give results equivalent to Schrödinger’s wave equations. Known for important Heisenberg Uncertainty Principle.	1925			Germany
	Erwin Schrödinger		Using concept of duality of matter, developed wave equations that, in theory, enable correct calculations of electron orbitals and properties. Practically speaking, solving the equations requires simplifying assumptions.	1926			Austria
	W. & I. Noddack, Otto Berg			1925	Rhenium		Germany		88	75
	Friedrich Hund		Produced Hund’s rule which enhance application of Bohr’s Aufbau Principle.	1927			Germany
	Paul Dirac		Formulated relativistic form of quantum mechanics that described energy levels of electrons.	1928			England
	Charles Janet		Developed left step periodic table. https://www.meta-synthesis.com/webbook/35_pt/pt_database.php?PT_id=152	1928			France
	James Chadwick		Confirmed existence of and determined the mass of the neutron.	1932			England
	Erwin Madelung		Madelung’s rule based on Janet’s suggestions gives order of filling of electron orbitals. https://www.meta-synthesis.com/webbook/35_pt/pt_database.php?PT_id=777	1936			Germany
	C. Perrier, E. G. Segre			1937	Technetium		Italy		89	43
			Otto Hahn and Fritz Strassmann discovered nuclear fission that was explained and predicted by Lise Meitner.	1937, 1938			Germany
	Hans Bethe		Discovered nuclear fusion in the sun.	1938			U.S. (N.Y.)
	M. Perey			1939	Francium		France		90	87
	D. R. Corson, K.R. Mackenzie, Emilio Segré			1940	Astatine		U.S. (CA)		91	85
	E. McMillan, P. H. Abelson			1940	Neptunium		U.S. (CA)		92	93
	Glenn Seaborg, E. McMillan, J. W. Kennedy, Arthur Wahl			1940	Plutonium		U.S. (CA)		93	94
	Glenn Seaborg, Ralph James, Albert Ghiorso			1944	Curium		U.S. (CA)		94	96
	Glenn Seaborg, Ralph A. James, L. O. Morgan Albert Ghiorso			1944	Americium		U.S. (CA)		95	95
	J. .A. Marinsky, L. E. Glendenin, C. D. Coryell			1945	Promethium		U.S. (TN)		96	61
	Emilio Gino Segrè		Produced chart of isotopes arranged by increasing atomic number. https://www.meta-synthesis.com/webbook/35_pt/pt_database.php?PT_id=231	1945			Italy, U.S.
	Glenn Seaborg		In addition to leading the group that used transmutation to synthesize many transuranium elements, produced most complete version of modern periodic table. https://www.meta-synthesis.com/webbook/35_pt/pt_database.php?PT_id=522	1945			U.S. (CA)
	S. Thompson, Albert Ghiorso, Glenn Seaborg.			1949	Berkelium		U.S. (CA)		97	97
	S. Thompson, Kenneth Street, Albert Ghiorso Glenn Seaborg			1950	Californium		U.S. (CA)		98	98
	Albert Ghiorso			1952	Einsteinium		U.S.		99	99
	Albert Ghiorso			1952	Fermium		U.S. (CA)		100	100
	Albert Ghiorso, Bernard Harvey, Gregory Choppin, S. Thompson, Glenn Seaborg			1955	Mendelevium		U.S. (CA)		101	101
	Albert Ghiorso, T. Sikkeland, Almon E. Larsh R. M. Latimer			1961	Lawrencium		U.S. (CA)		102	103
	Maria G. Mayer, Hans Jensen		Developed nuclear shell model that contributes to understanding of nuclear stability.	1963			U.S., Germany
	M. Gell-Mann, G. Zweig		Proposed quark model. Although not needed to explain the periodic table, quarks enhance our understanding of the nucleus.	1964			U.S.
	Georgy Flerov			1964	Rutherfordium		USSR		103	104
	Georgy Flerov			1966	Nobelium		USSR		104	102
	disputed			1967	Dubnium		USSR or U.S.		105	105
	Albert Ghiorso, Y. Oganessian			1974	Seaborgium		U.S. (CA) or Russia		106	106
	P. Armbruster, G. Münzenber			1981	Bohrium		Germany		107	107
	P. Armbruster, G. Münzenber			1982	Meitnerium		Germany		108	109
	P. Armbruster, G. Münzenber			1984	Hassium		Germany		109	108
	S. Hofmann, P. Armbruster, G. Münzenber			1994	Darmstadtium		Germany		110	110
	P. Armbruster, G. Münzenber			1994	Roentgenium		Germany		111	111
	S.Hofmann, Victor Ninov			1996	Copernicium		Germany		112	112
	Y. Oganessian			1998	Flerovium		Russia		113	114
	Y. Oganessian Ken Moody			2000	Livermorium		Russia,U.S.		114	116
	Y. Oganessian Ken Moody			2003	Moscovium		Russia, U.S.		115	115
	Y. Oganessian			2006	Oganesson		Russia		116	118
	Y. Oganessian			2010	Tennessine		Russia, U.S.		117	117
	Kosuke Morita			2012	Nihonium		Japan		118	113
	Mark Winter		Produces continuously updated website devoted to the Periodic Table. https://www.webelements.com/	1993 - current			England
	Eric R. Scerri		The Periodic Table: Its Story and Its Significance, Oxford University Press, N.Y. A history of the development of the periodic table. https://www.chemistry.ucla.edu/directory/scerri-eric-r https://www.scientificamerican.com/article/the-evolution-of-the-periodic-system/	2007			U.S.
	Mark R. Leach		Updates hot links to most periodic table websites and element discoveries. https://www.meta-synthesis.com/webbook/35_pt/pt_database.php?Button=All	2003- current			England
	Theodore Gray		http://periodictable.com/index.html For an extensive list of periodic properties with graphing capabilities, visit: http://periodictable.com/Properties/A/CrustAbundance.htm	current			U.S.

¹Images of most contributors of concepts included but not discoverers of elements with the exceptions of Marie Curie and William Ramsay

²RGB codes used for colors of elements taken from Chemicool. Color is unknown but suspected to be silvery for elements with dark blue font.

³Number of known elements.

Three thead timeline for the development of the periodic table, atomic structure and electronic theory.

Year	#¹	Concept of the atom	Periodic table based on properties	Theory of Periodic Table

440 BC	11	Democritus, Leucippus suggested that matter is made up of indivisible particles called “atomos”.
340 BC	11	Aristotle, Plato reject atomos concept and claim matter is continuous. Continuity of matter concept dominates for 2100 years until evidence emerges in support of the atomic theory (1803).
1778	23		Antoine. Lavoisier demonstrates conservation of mass (within detectable limits) in chemical reactions and prepares list of 33 substances including 23 elements arranged according to properties (gases, non-metals, metals, earths) http://www.meta-synthesis.com/webbook/35_pt/pt_database.php?PT_id=3
1794	31	Jeremias B. Richter and Joseph Proust discovered laws of definite proportions and constant composition.
1803	41	Results of Richter and Proust are inconsistent with continuity concept of matter but explainable using atomos concept. John Dalton introduced empirically based atomic theory. 1. Elements are made of extremely small particles called atoms. 2. Atoms of a given element are the same in size, mass and other properties; atoms of different elements differ in size, mass and other properties. 3. Atoms cannot be subdivided, created or destroyed. 4. Atoms of different elements combine in simple whole-number ratios to form chemical compounds. 5. In chemical reactions, atoms are combined, separated or rearranged.
1815	47		William Prout proposed concept that atomic weights of elements are whole-number multiples of the atomic weight of hydrogen suggesting that all elements are composed of hydrogen atoms.
1829	54		Johann W. Döbereiner demonstrated concept of triads, groups of elements (later realized to be in the same group) in which the mass of the middle element was close to the average of the masses of the first and third element.
1843	55		Leopold Gmelin using the concept of triads, developed a table of 55 elements in a periodic system that contained many of the important relationships of our modern periodic table. https://www.meta-synthesis.com/webbook/35_pt/pt_database.php?PT_id=268
1860	59		Stanislao Cannizzaro played important role in establishing useful table of atomic masses that enabled development within a decade of several periodic tables.
1862-1867	62		A.-É. Béguyer de Chancourtois, F. Reich, H. T. Richter, John Newlands, William Odling, Gustavus Hinrichs ordered elements according to increasing atomic mass in charts that demonstrated periodic properties of the elements. https://www.meta-synthesis.com/webbook/35_pt/pt_database.php?Button=All
1868- 1870	63		Dimitri Mendeleev and independently Lothar Meyer published predecessors of modern periodic table with elements ordered by atomic mass and groups determined by chemical properties. https://www.meta-synthesis.com/webbook/35_pt/pt_database.php?PT_id=9 https://www.meta-synthesis.com/webbook/35_pt/pt_database.php?PT_id=12
1886	75	William Crookes suggested atomic weights are an average of different kinds of atoms of the same element (concept of isotopes). Crookes in 1875 also developed Crookes’ tube which enabled discovery of electron (1897)
1886	75	Eugen Goldstein discovered rays that were eventually realized to be hydrogen nuclei or protons.
1895	76	W. Röntgen discovered X-rays.
1896	77	H. Becquerel discovered radioactivity that enabled Marie Curie and others to isolate radioactive elements and for Rutherford to design gold foil expt.
1897	77	J. J. Thomson using Crookes’ tube discovers electron and determines e/m ratio.
1898	80		With her husband Pierre, Marie Curie discovered polonium and later other radioactive elements that filled in gaps in periodic table.
1900	84			Max Planck initiated modern era of quantum mechanics when he showed that energy did not flow in a steady continuum, but was delivered in discrete packets called quanta with E = hn.
1902	84		William Ramsay and co-workers discovery of inert gases in late 1890’s (helium observed in sun in 1868 but isolated by William Ramsay and Raleigh in 1895) led Ramsay, Mendeleev and others to add inert gases to periodic table. See: https://www.meta-synthesis.com/webbook/35_pt/pt_database.php?Button=All
1904	84	J. J. Thomson proposes “plum pudding” model of atom.
1904	84	Hantaro Nagaoka proposed solar system like model of the atom that was not accepted until gold foil experiment of Rutherford in 1911. In 1907, Jean Baptiste Perrin also promoted solar system model for atom.
1905	84		Alfred Werner presented periodic table with substantial resemblance to most popular form used today. https://www.meta-synthesis.com/webbook/35_pt/pt_database.php?PT_id=64	Albert Einstein showed that light which had been considered a form of electromagnetic waves, must also be thought of as particle-like (photons). Einstein’s relativity theories also are important considerations in electron orbitals of high atomic number.
1907	85		Antonius Johannes van den Broek was the first to change ordering of elements from atomic mass to nuclear charge (later called atomic number).
1908	85	Robert Millikan’s oil drop experiment determined charge on electron and enabled calculation of mass of electron from Thomson’s e/m ratio.
1911	85	Ernest Rutherford performed gold foil experiment that demonstrated nuclear model for atom with tiny nucleus with almost all of the mass of the atom. Before gold foil experiment, he showed that alpha particles are helium nucleii. Also often given credit for discovery of proton (however, see Goldstein in 1886)
1912	85	Frederick Soddy worked with Rutherford and elevated Crooke’s suggestion (1886) of isotopes into a theory. In 1913, Hevesy and Paneth provided evidence that isotopes chemically behave the same.
1913	85	Henry Moseley using X-rays, demonstrated that the number of protons (atomic number) as suggested by van den Broek instead of atomic mass is the correct basis for the ordering of the elements.		Niels Bohr applied quantum theory to atoms. Using a planetary model, derived a correct mathematical description of the electron in hydrogen but model failed for multiple electron atoms. Proposed Aufbau Principle. Attempted to use electron structure with two quantum numbers (n, l) to explain shape of periodic table.
1922	86	Francis Aston invented mass spectrometer and using it, was the first to experimentally demonstrate existence of isotopes of many elements.	Niels Bohr produced symmetrical periodic table that improved tables of T. Bayley and J. J. Thomson and was improved again by E. Scerri in 1997. https://www.meta-synthesis.com/webbook/35_pt/pt_database.php?PT_id=19
1924	87			Edmund Stoner improved Bohr’s attempt to correlate periodic table with electron theory by adding a third quantum number (n, l, m).
1924	87			Wolfgang Pauli added spin quantum number to make 4 quantum numbers (n, l, m, s) that enable strong correlation of electron orbital theory with experimental properties and shape of periodic table. Introduced Pauli Exclusion Principle (all electrons for an atom must have distinct set of quantum numbers).
1924	87			Louis-Victor de Broglie showed wave nature of electrons and all matter.
1925, 1926	87			Werner Heisenberg and Erwin Schrödinger using different approaches, developed wave mechanical equations for correctly describing electronic orbitals. Practically speaking, equations are extremely difficult to solve without making simplifying assumptions.
1927	88			Friedrich Hund produced Hund’s rule (every orbital in a sublevel is singly occupied before any orbital is doubly occupied) which enhanced application of Bohr’s Aufbau Principle.
1928	88		Charles Janet developed left step periodic table. https://www.meta-synthesis.com/webbook/35_pt/pt_database.php?PT_id=152	Paul Dirac formulated relativistic form of quantum mechanics that described energy levels of electrons.
1932	88	James Chadwick confirmed existence of and determined the mass of the neutron.
1936	88			Erwin Madelung’s rule based on Janet’s suggestions gives order of filling of electron orbitals. https://www.meta-synthesis.com/webbook/35_pt/pt_database.php?PT_id=777
1936 ...			Nuclear reactions including transmutation, nuclear fission and nuclear fusion are discovered and exploited.
1945	96	Emilio Gino Segrè produced chart of isotopes arranged by increasing atomic number. https://www.meta-synthesis.com/webbook/35_pt/pt_database.php?PT_id=231	Glenn Seaborg, in addition to leading the group that used transmuation to synthesize many transuranium elements, produced most complete version of modern periodic table. https://www.meta-synthesis.com/webbook/35_pt/pt_database.php?PT_id=522
1963	102	Maria G. Mayer, Hans Jensen developed nuclear shell model that contributes to understanding of nuclear stability.
1964	102	M. Gell-Mann, George Zweig proposed quark model. Although not needed to explain the periodic table, quarks enhance our understanding of the nucleus.
2007	116		Eric R. Scerri authors The Periodic Table: Its Story and Its Significance, Oxford University Press, N.Y. A history of the development of the periodic table. https://www.chemistry.ucla.edu/directory/scerri-eric-r https://www.scientificamerican.com/article/the-evolution-of-the-periodic-system/
1993- 2018	109 118		Mark Winter posted website devoted to the Periodic Table that is continually updated. https://www.webelements.com/
2003 2018	114 118		Mark R. Leach posted hot links to most periodic table sites and element discoveries. https://www.meta-synthesis.com/webbook/35_pt/pt_database.php?Button=Al .
... 2018	118		Theodore Gray provides commercially available beautiful periodic tables and website with extensive list of properties with grpahing capibilities. http://periodictable.com/index.html http://periodictable.com/Properties/A/CrustAbundance.html

¹images generally only provided for conceptual contributions and not for discoverers of elements (exceptions include Curie and Ramsay)

²number of known elements discovered by the year indicated.

The excellent book by Eric R. Scerri (The Periodic Table: Its Story and Its Significance, 2007, Oxford University Press, N.Y.) and the web site of Mark Leach

(https://www.meta-synthesis.com/webbook/35_pt/pt_database.php?Button=All)

were the sources of much of the information included in the timelines.

Medium-long forms of the periodic table with element colors.

A limited search for a periodic table with the colors of the elements has not yet located a table of this type. However, Theodore Gray has produced many wonderful tables including one with images of authentic samples of the elements (http://periodictable.com/) and a commercially available model that contains sample of most of the elements (http://www.periodictable.co.uk/). While the tables below are not nearly as fascinating or interesting as Gray's tables, the tables below have been designed to enable viewers to focus on the property of color. Most of the colors have been extracted from https://www.chemicool.com/ primarily because it often included a two word description of the color. Other sites referred to were Theodore Gray's http://periodictable.com/Properties/A/Color.html and Mark Winter's https://www.webelements.com/. For some elements, the colors listed on Internet sites are not always in agreement. Rene Vernon, the author of a paper on metalloids, https://pubs.acs.org/doi/pdfplus/10.1021/ed3008457 has contributed valuable comments about the colors of boron, phosphorus, iodine, cesium and astatine. Some of these color issues are because the most stable allotrope (e.g., phosphorus) is not always the most abundant allotrope.

boron - the most stable allotrope of boron is the beta rhombohedral crystalline state. Colors reported for this state range from shiny silver-grey to grey to dark to black. It is represented as dark grey below.

phosphorus - the most stable allotrope is black but the most common form is described as white to pale yellow. A very light yellow has been used below with a black insert.

iodine - while silver is sometimes mentioned, the overwhelming consensus is that iodine crystals are in the violet or purple range.

astatine - although astatine has been observed, due to its transient existence, it has apparently not been possible to determine its color. Some web sites conclude that it should have some metallic properties and as a result have a silvery color. Other web sites suggest as progression is made down group 7A (17), the color continuously darkens with a presumption that astatine should be near black. It is left in these tables as unknown like francium and the elements with atomic numbers above 99.

Selected periodic properties of the elements (ionization energy, atomic radius, valence).

For an extensive list of periodic properties with graphing capabilities please visit:

http://periodictable.com/Properties/A/CrustAbundance.html .

Some periodic table questions and unresolved issues.

1. There are at least four commonly used versions of the periodic table: the long, the medium-long, the left step, and the pyramidal. While some experts have preferences for one or another, each has strengths and weaknesses. Which one do you prefer and why?

medium-long and long (not up-to-date with names)

https://www.meta-synthesis.com/webbook/35_pt/pt_database.php?PT_id=371 (medium long and long but not up-to-date with names)

long form

https://commons.wikimedia.org/wiki/File:Periodic_table_large-long.svg

https://kaiserscience.wordpress.com/chemistry/the-periodic-table/alternative-periodic-tables/

medium-long form

https://iupac.org/what-we-do/periodic-table-of-elements/

https://www.webelements.com/

http://murov.info/pertab-trad.pdf

left step

https://jeries.rihani.com/symmetry/index6c.html

pyramidal version (not up-to-date with names)

https://www.meta-synthesis.com/webbook/35_pt/pt_database.php?PT_id=19

2. The positions of some elements in periodic tables are still disputed.

a. Does hydrogen belong in the alkali metals group or the halogen group or neither?

b. There are some claims that second period elements have properties inconsistent with the remaining members of their groups. Explain this statement.

c. Some medium-long periodic tables have lanthanum part of the “f” group of elements (split out from the periodic table), others have lutetium as a member of the 14 elements and still others include 15 elements in the “f” group . What is the best placement of these two elements? Part of the issue is the priority of chemical properties versus electronic structure. If electronic structure is taken as the determining criteria, are there other elements that are misplaced in the periodic table?

3. The IUPAC numbers the groups from 1 through 18 but American periodic tables often have A and B group elements with the numbers running from 1A through 8A and 1B through 8B. State the advantages and disadvantages of each and your preference (for a table with both, see tables above or: http://murov.info/pertab-trad.pdf.

4. Is the periodic table universal or could there be differences on another planet? For example, consider the universality of atomic masses.

5. Does the periodic table contain any isotope information? Consider use of the atomic mass as a source of isotope information (See: S. Murov, Chem 13 News, March, 2010. “Promoting Insight: Atomic Mass”.

6. The periodic tables above attempt to illustrate the approximate colors of the elements. The orange staircase in the two periodic tables is commonly included in many periodic tables to very qualitatively separate the metals and the non-metals. Do the colors of the elements also help to distinguish metals from non-metals and, if so, does this method correlate with the staircase model? Which method do you think has more merit? (Note: It is often suggested that the elements adjacent to the staircase are metalloids, semiconductors and/or semimetals. The consensus is that boron, silicon, germanium, arsenic, antimony and tellurium are metalloids with a few others in the questionable category. For a discussion of criteria used to characaterize metalloid properties, please see: https://pubs.acs.org/doi/pdfplus/10.1021/ed3008457 ).

7. Calculations indicate that stability of nuclei depend on the neutron to proton ratio and predict an island of stability above atomic number 110. Is it possible that there are some “longer lived isotopes” with atomic number above 110? (e.g., see: https://en.wikipedia.org/wiki/Island_of_stabilitybeyond_118)

8. What is the probability that elements with atomic number greater than 118 will ever be synthesized?

(e.g., see: https://www.chemistryworld.com/news/beyond-element-118-the-next-row-of-the-periodic-table/9400.article

9. In some cases, discoveries have been made virtually simultaneously by different people in different countries (e.g., 1772, 1963). Is this just a coincidence or are other factors in play here?

Suggestions, corrections and comments will be appreciated. Please send them to Steven Murov at: murovs@yosemite.edu
For a list of web sites posted by Steven Murov, please visit: http://murov.info/ .

For a Periodic table website, please visit: https://www.meta-synthesis.com/webbook/35_pt/pt_database.php?Button=Al , http://murov.info/periodictables.htm

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