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Chemistry of the Elements (Greenwood, NN; Earshaw, A.)
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The popular  periodic table layout, also known as the common or standard form as shown at various other points in this article , is attributable to Horace Groves Deming. In , Deming, an American chemist, published short Mendeleev style and medium column form periodic tables. By the s Deming's table was appearing in handbooks and encyclopedias of chemistry. It was also distributed for many years by the Sargent-Welch Scientific Company. With the development of modern quantum mechanical theories of electron configurations within atoms, it became apparent that each period row in the table corresponded to the filling of a quantum shell of electrons.
Larger atoms have more electron sub-shells, so later tables have required progressively longer periods. In , Glenn Seaborg , an American scientist, made the suggestion that the actinide elements , like the lanthanides , were filling an f sub-level. Before this time the actinides were thought to be forming a fourth d-block row. Seaborg's colleagues advised him not to publish such a radical suggestion as it would most likely ruin his career.
As Seaborg considered he did not then have a career to bring into disrepute, he published anyway. Seaborg's suggestion was found to be correct and he subsequently went on to win the Nobel Prize in chemistry for his work in synthesizing actinide elements. Although minute quantities of some transuranic elements occur naturally,  they were all first discovered in laboratories.
Their production has expanded the periodic table significantly, the first of these being neptunium , synthesized in There have been controversies concerning the acceptance of competing discovery claims for some elements, requiring independent review to determine which party has priority, and hence naming rights. It, along with nihonium element , moscovium element , and oganesson element , are the four most recently named elements, whose names all became official on 28 November The modern periodic table is sometimes expanded into its long or column form by reinstating the footnoted f-block elements into their natural position between the s- and d-blocks.
Unlike the column form this arrangement results in "no interruptions in the sequence of increasing atomic numbers". Within years of the appearance of Mendeleev's table in , Edward G. Mazurs had collected an estimated different published versions of the periodic table. Such alternatives are often developed to highlight or emphasize chemical or physical properties of the elements that are not as apparent in traditional periodic tables.
A popular  alternative structure is that of Otto Theodor Benfey The elements are arranged in a continuous spiral, with hydrogen at the centre and the transition metals, lanthanides, and actinides occupying peninsulas.
Most periodic tables are two-dimensional;  three-dimensional tables are known to as far back as at least pre-dating Mendeleev's two-dimensional table of The various forms of periodic tables can be thought of as lying on a chemistry—physics continuum. This has a structure that shows a closer connection to the order of electron-shell filling and, by association, quantum mechanics. This is regarded as better expressing empirical trends in physical state, electrical and thermal conductivity, and oxidation numbers, and other properties easily inferred from traditional techniques of the chemical laboratory.
Simply following electron configurations, hydrogen electronic configuration 1s 1 and helium 1s 2 should be placed in groups 1 and 2, above lithium 1s 2 2s 1 and beryllium 1s 2 2s 2. As the group changed its formal number, many authors continued to assign helium directly above neon, in group 18; one of the examples of such placing is the current IUPAC table. The position of hydrogen in group 1 is reasonably well settled.
Like lithium, it has a significant covalent chemistry. Nevertheless, it is sometimes placed elsewhere. A common alternative is at the top of group 17  given hydrogen's strictly univalent and largely non-metallic chemistry, and the strictly univalent and non-metallic chemistry of fluorine the element otherwise at the top of group Sometimes, to show hydrogen has properties corresponding to both those of the alkali metals and the halogens, it is shown at the top of the two columns simultaneously. The other period 1 element, helium, is occasionally placed separately from any group as well.
Although scandium and yttrium are always the first two elements in group 3, the identity of the next two elements is not completely settled. They are commonly lanthanum and actinium , and less often lutetium and lawrencium. The two variants originate from historical difficulties in placing the lanthanides in the periodic table, and arguments as to where the f block elements start and end.
Chemical and physical arguments have been made in support of lutetium and lawrencium   but the majority of authors seem unconvinced. Lanthanum and actinium are commonly depicted as the remaining group 3 members. The configurations of caesium , barium and lanthanum are [Xe]6s 1 , [Xe]6s 2 and [Xe]5d 1 6s 2. Lanthanum thus has a 5d differentiating electron and this establishes it "in group 3 as the first member of the d-block for period 6".
Still in period 6, ytterbium was assigned an electron configuration of [Xe]4f 13 5d 1 6s 2 and lutetium [Xe]4f 14 5d 1 6s 2 , "resulting in a 4f differentiating electron for lutetium and firmly establishing it as the last member of the f-block for period 6". This meant that ytterbium and lutetium—the latter with [Xe]4f 14 5d 1 6s 2 —both had 14 f-electrons, "resulting in a d- rather than an f- differentiating electron" for lutetium and making it an "equally valid candidate" with [Xe]5d 1 6s 2 lanthanum, for the group 3 periodic table position below yttrium.
In terms of chemical behaviour,  and trends going down group 3 for properties such as melting point, electronegativity and ionic radius,   scandium, yttrium, lanthanum and actinium are similar to their group 1—2 counterparts. In this variant, the number of f electrons in the most common trivalent ions of the f-block elements consistently matches their position in the f-block.
In other tables, lutetium and lawrencium are the remaining group 3 members. It has been argued that this is not a valid concern given other periodic table anomalies—thorium, for example, has no f-electrons yet is part of the f-block. Such a configuration represents another periodic table anomaly, regardless of whether lawrencium is located in the f-block or the d-block, as the only potentially applicable p-block position has been reserved for nihonium with its predicted configuration of [Rn]5f 14 6d 10 7s 2 7p 1. Chemically, scandium, yttrium and lutetium and presumably lawrencium behave like trivalent versions of the group 1—2 metals.
For example, the f-electron counts for the first five f-block elements are La 0, Ce 1, Pr 3, Nd 4 and Pm 5. A few authors position all thirty lanthanides and actinides in the two positions below yttrium usually via footnote markers. This variant, which is stated in the Red Book to be the IUPAC-agreed version as of a number of later versions exist, and the last update is from 1st Dec.
This arrangement is consistent with the hypothesis that arguments in favour of either Sc-Y-La-Ac or Sc-Y-Lu-Lr based on chemical and physical data are inconclusive. The definition of a transition metal , as given by IUPAC, is an element whose atom has an incomplete d sub-shell, or which can give rise to cations with an incomplete d sub-shell. The IUPAC definition therefore excludes group 12, comprising zinc, cadmium and mercury, from the transition metals category. Some chemists treat the categories " d-block elements" and "transition metals" interchangeably, thereby including groups 3—12 among the transition metals.
In this instance the group 12 elements are treated as a special case of transition metal in which the d electrons are not ordinarily involved in chemical bonding. The report of mercury IV fluoride HgF 4 , a compound in which mercury would use its d electrons for bonding, has prompted some commentators to suggest that mercury can be regarded as a transition metal.
As such, mercury could not be regarded as a transition metal by any reasonable interpretation of the ordinary meaning of the term. Still other chemists further exclude the group 3 elements from the definition of a transition metal. They do so on the basis that the group 3 elements do not form any ions having a partially occupied d shell and do not therefore exhibit any properties characteristic of transition metal chemistry.
Though the group 3 elements show few of the characteristic chemical properties of the transition metals, they do show some of their characteristic physical properties on account of the presence in each atom of a single d electron. Although all elements up to oganesson have been discovered, of the elements above hassium element , only copernicium element , nihonium element , and flerovium element have known chemical properties, and only for copernicium is there enough evidence for a conclusive categorisation at present.
The other elements may behave differently from what would be predicted by extrapolation, due to relativistic effects; for example, flerovium has been predicted to possibly exhibit some noble-gas-like properties, even though it is currently placed in the carbon group. It is unclear whether new elements will continue the pattern of the current periodic table as period 8 , or require further adaptations or adjustments.
Seaborg expected the eighth period to follow the previously established pattern exactly, so that it would include a two-element s-block for elements and , a new g-block for the next 18 elements, and 30 additional elements continuing the current f-, d-, and p-blocks, culminating in element , the next noble gas. There are currently several competing theoretical models for the placement of the elements of atomic number less than or equal to In all of these it is element , rather than element , that emerges as the next noble gas after oganesson, although these must be regarded as speculative as no complete calculations have been done beyond element The number of possible elements is not known.
A very early suggestion made by Elliot Adams in , and based on the arrangement of elements in each horizontal periodic table row, was that elements of atomic weight greater than circa which would equate to between elements 99 and in modern-day terms did not exist.
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The Bohr model exhibits difficulty for atoms with atomic number greater than , as any element with an atomic number greater than would require 1s electrons to be travelling faster than c , the speed of light. The relativistic Dirac equation has problems for elements with more than protons. For such elements, the wave function of the Dirac ground state is oscillatory rather than bound, and there is no gap between the positive and negative energy spectra, as in the Klein paradox.
For heavier elements, if the innermost orbital 1s is not filled, the electric field of the nucleus will pull an electron out of the vacuum, resulting in the spontaneous emission of a positron. The many different forms of periodic table have prompted the question of whether there is an optimal or definitive form of periodic table. An objective basis for chemical periodicity would settle the questions about the location of hydrogen and helium, and the composition of group 3.
Such an underlying truth, if it exists, is thought to have not yet been discovered. In its absence, the many different forms of periodic table can be regarded as variations on the theme of chemical periodicity, each of which explores and emphasizes different aspects, properties, perspectives and relationships of and among the elements. In celebration of the periodic table's th anniversary, the United Nations declared the year as the International Year of the Periodic Table, celebrating "one of the most significant achievements in science".
From Wikipedia, the free encyclopedia. This article is about the table used in chemistry and physics. For other uses, see Periodic table disambiguation. Tabular arrangement of the chemical elements ordered by atomic number. Periodic table forms. Periodic table history. Dmitri Mendeleev predictions. Sets of elements. By periodic table structure. Groups 1— By metallic classification. By other characteristics. Coinage metals Platinum-group metals.
List of chemical elements. Properties of elements. Atomic weight Crystal structure. Data pages for elements. Periodic table large cells, column layout. Main article: Group periodic table. Groups in the Periodic table. Elements of the group have one s-electron in the outer electron shell. Hydrogen has no analogs and is not considered to be an alkali metal as it rarely exhibits behaviour comparable to that of the alkali metals.
This makes the group somewhat exceptional. Later , Mendeleev accepted the evidence for their existence, and they could be placed in a new "group 0", consistently and without breaking the periodic table principle. Main article: Period periodic table. Main article: Block periodic table. Main article: Periodic trends.
Main article: Electronic configuration. Main article: Atomic radius. Main article: Ionization energy. Main article: Electronegativity. Main article: Electron affinity. Main article: History of the periodic table. Dmitri Mendeleev , watercolour by Ilya Repin. Main article: Alternative periodic tables.
The experimentally determined electron configurations of the elements differ from the configurations predicted by the Madelung rule in twenty instances. Main article: Extended periodic table. Periodic table with eight rows, extended to element . Chemistry portal. Abundance of the chemical elements Atomic electron configuration table Element collecting List of chemical elements List of periodic table-related articles Names for sets of chemical elements Standard model Table of nuclides Template:Spectral lines of the elements The Mystery of Matter: Search for the Elements PBS film Timeline of chemical element discoveries.
Thus, helium is shown in the p-block but is actually an s-block element, and for example the d-subshell in the d-block is actually filled by the time group 11 is reached, rather than group Adams omits the rare earths and the "radioactive elements" i. See: Elliot Q. Journal of the American Chemical Society.
Most investigators considered that these elements were analogues of the third series transition elements, hafnium, tantalum and tungsten. The existence of a second inner transition series, in the form of the actinides, was not accepted until similarities with the electron structures of the lanthanides had been established. See: van Spronsen, J. The periodic system of chemical elements. Amsterdam: Elsevier.
This arrangement was referred to as the "asteroid hypothesis", in analogy to asteroids occupying a single orbit in the solar system. Before this time the lanthanides were generally and unsuccessfully placed throughout groups I to VIII of the older 8-column form of periodic table. Although predecessors of Brauner's arrangement are recorded from as early as , he is known to have referred to the "chemistry of asteroids" in an letter to Mendeleev.
Other authors assigned all of the lanthanides to either group 3, groups 3 and 4, or groups 2, 3 and 4. In Niels Bohr continued the detachment process by locating the lanthanides between the s- and d-blocks. In Glenn T. Seaborg re introduced the form of periodic table that is popular today, in which the lanthanides and actinides appear as footnotes. Seaborg first published his table in a classified report dated It was published again by him in in Chemical and Engineering News , and in the years up to several authors commented on, and generally agreed with, Seaborg's proposal.
In that year he noted that the best method for presenting the actinides seemed to be by positioning them below, and as analogues of, the lanthanides. See: Thyssen P. Gschneider Jr. Handbook on the Physics and Chemistry of the Rare Earths. Amsterdam: Elsevier, pp. Origin of the Actinide Concept'. Holt Chemistry. Essential Chemistry 2nd ed. Descriptive Inorganic Chemistry 6th ed. New York: W. Chemistry: The Central Science 11th ed. Thus, among the Group 2 alkaline earth metals , Mg less basic belongs in the "soluble group" and Ca, Sr and Ba more basic occur in the "ammonium carbonate group".
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