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===Metallic character===

The lower the values of ionization energy, electronegativity and electron affinity, the more [[metal]]lic character the element has. Conversely, nonmetallic character increases with higher values of these properties.<ref>{{cite book |last1=Yoder |first1=C. H. |last2=Suydam |first2=F. H. |last3=Snavely |first3=F. A. |year=1975 |title=Chemistry |page=[https://archive.org/details/chemistry00clau/page/58 58] |edition=2nd |publisher=Harcourt Brace Jovanovich |isbn=978-0-15-506465-2 |url=https://archive.org/details/chemistry00clau/page/58 }}</ref> Given the periodic trends of these three properties, metallic character tends to decrease going across a period (or row) and, with some irregularities (mostly) due to poor screening of the nucleus by d and f electrons, and [[Relativistic quantum chemistry|relativistic effects]],<ref>Huheey, Keiter & Keiter, pp. 880–85</ref> tends to increase going down a group (or column or family). Thus, the most metallic elements (such as [[caesium]]) are found at the bottom left of traditional periodic tables and the most nonmetallic elements (such as [[neon]]) at the top right. The combination of horizontal and vertical trends in metallic character explains the stair-shaped [[dividing line between metals and nonmetals]] found on some periodic tables, and the practice of sometimes categorizing several elements adjacent to that line, or elements adjacent to those elements, as [[metalloid]]s.<ref>{{cite book |last=Sacks|first=O.|title=Uncle Tungsten: Memories of a chemical boyhood|year=2009|publisher=Alfred A. Knopf |location=New York|isbn=978-0-375-70404-8|pages=191, 194}}</ref><ref>Gray, p. 9</ref>

===Analogies between categories===

{| style="float: right; margin-left: 50px;"

|+ '''Periodic table category counterparts'''

| ||style="text-align:center"| Noble gases He, Ne, Ar, Kr, Xe, Rn ||

| Active metals Groups 1−3+, Ln, An, (Al) || ||style="text-align:right"| Halogens F, Cl, Br, I

| Transition metals Most of them || ||style="text-align:right"| Other nonmetals H, C, N, O, P, S, Se

| Other (Al), Sn, Bi etc || ||style="text-align:right"| Metalloids B, Si, Ge, As, Sb, Te

| || style="text-align:center"|[[Noble metal]]s Ru, Rh, Pd, Os, Ir, Pt, Au ||

A traditional aspect of teaching the periodic table is to contrast the alkali metals with the halogens. For the noble gases, they have their counterparts in the noble metals.<ref>{{cite book |last=Wiberg|first=N.|title= Inorganic Chemistry|year=2001|page=1133|publisher=Academic Press|isbn=978-0-12-352651-9|location=San Diego}}</ref> This approach can be extended.<ref>{{cite journal |last=Vernon |first=R |date=2020 |title=Organising the metals and nonmetals|journal=Foundations of Chemistry |volume=22 |pages=217–233 |doi=10.1007/s10698-020-09356-6}}</ref> The "active" metals are mostly strongly electropositive metals, with a few of the actinoids being only moderately electropositive. The transition metals are, for the most part, moderately to weakly electropositive in nature. A small number, such as zirconium are more strongly electropositive; several others are chemically very weak (or noble), like platinum, with these representing the noble metals. Most of the other metals such as tin and bismuth, are chemically weak. A minority are moderately electropositive (zinc, for example).<ref>{{cite book |last1=Kneen |first1=W.R. |last2=Rogers |first2=M.J.W. |last3=Simpson |first3=P. |date= 1972|title=Chemistry: Facts, Patterns and Principles |location= London|publisher=Addison-Wesley |pages= 264, 489, 525}}</ref>

The other nonmetals are neither as reactive as the halogens nor as chemically restrained as the weakly nonmetallic metalloids.

===Isodiagonality===

[[File:32 column La table with diagonals.jpg|thumb|upright=1.8|right|32-column lanthanum table (condensed) showing examples of isodiagonality. Aluminium has been shifted to Group 3, for this purpose. An isodiagonal relationship can be seen, for example, along calcium-yttrium-cerium. All three elements are strongly basic. Similarities between calcium and the lanthanoids (including cerium) are well known. Yttrium is a member of the rare earths, as are the lanthanoids. All three elements exhibit predominantly ionic chemistry. In atomic number terms the three elements form a [[Döbereiner's triads|triad]]: 20 (Ca) +58 (Ce) = 78; 78/2 = 39 (Y). Scandium-yttrium-lanthanum too form such a triad: 21 (Sc) +57 (La) = 78/2 = 39 (Y).<ref name="Vernon 2020">{{cite journal |last1=Vernon |first1=René E. |title=The location and composition of Group 3 of the periodic table |journal=Foundations of Chemistry |date=24 September 2020 |doi=10.1007/s10698-020-09384-2 |url=https://link.springer.com/article/10.1007/s10698-020-09384-2 |language=en |issn=1572-8463}} [[File:CC-BY icon.svg|50px]] Text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref>]]

Isodiagonality refers to diagonal relationships in the periodic table seen between elements including lithium and magnesium; beryllium and aluminium; and boron and silicon.<ref name="Vernon 2020"/><ref>{{cite journal |last=Rayner-Canham |first=G. |date=2011 |title=Isodiagonality in the periodic table |journal=Foundations of Chemistry |volume=13 |issue=2 |pages=121–129 |doi=10.1007/s10698-011-9108-y}}{{cite book |last1=Rayner-Canham |first1=G.|date=2020 |title=The Periodic Table: Past, Present, and Future|edition=|publisher =World Scientific |location=New Jersey |isbn= 978-981-121-848-4 |pages=213–234}}</ref> Such relationships were recognized by both Mendeleev and Newlands. They are, in some ways:

:"…a general attribute of the properties of the chemical elements. For example, the metal-nonmetal divide forms an almost diagonal demarcation."<ref name="Vernon 2020"/><ref>{{cite journal |last1=Edwards |first1=P. P. |last2=Sienko |first2=M. J. |date=1983 |title=On the Occurrence of Metallic Character in the Periodic Table of the Elements|journal=Journal of Chemical Education|volume=60 |issue=9 |pages=691–696 |doi=10.1021/ed060p691}}</ref>

Mingos counts diagonal relationships as one of the three patterns that characterise the periodic table, along with vertical and horizontal trends.<ref name="Vernon 2020"/><ref>{{cite book |last1=Mingos |first1=D. M. P.|date=1998 |title=Essential Trends in Inorganic Chemistry|edition=|publisher =Oxford University Press|location=Oxford |isbn=978-0-19-850108-4 |pages=213–234}}</ref>

===Linking or bridging groups===

{{Periodic table (micro)|mark=Sc, Y, La, Ac, Zr, Hf, Rf, Nb, Ta, Db, Lu, Lr, Cu, Ag, Au, Zn, Cd, Hg, He, Ne, Ar, Kr, Xe, Rn|caption=32-column periodic table showing, from left to right, the location of group 3; the heavy group 4 and 5 elements; lutetium and lawrencium; groups 11–12; and the noble gases}}

</div>

From left to right across the four blocks of the long- or 32-column form of the periodic table are a series of linking or bridging groups of elements, located approximately between each block. In general, groups at the peripheries of blocks display similarities to the groups of the neighbouring blocks as well as to the other groups in their own blocks, as expected as most periodic trends are continuous.<ref name="MacKay">{{cite book |last1=MacKay |first1=K. M.|last2=MacKay |first2=R. A. |last3=Henderson |first3=W. |date=2002 |title=Introduction to Modern Inorganic Chemistry|edition=6th|publisher =Nelson Thornes|location=Cheltenham|isbn=978-0-7487-6420-4|pages=194–96}}</ref> These groups, like the metalloids, show properties in between, or that are a mixture of, groups to either side. Chemically, the group 3 elements, lanthanides, and heavy group 4 and 5 elements show some behaviour similar to the alkaline earth metals<ref>{{cite book |last=Remy |first=H.|date=1956 |title=Treatise on Inorganic Chemistry |volume=2|location=Amsterdam |publisher=Elsevier |page=30|editor-last=Kleinberg|editor-first=J.}}</ref> or, more generally, ''s'' block metals<ref>{{cite book |last1=Phillips |first1=C. S. G.|last2=Williams|first2=R. J. P.|date=1966 |title=Inorganic Chemistry|location=Oxford |publisher=Clarendon Press |pages=4–5}}</ref><ref>{{cite book |last=King |first=R. B.|date=1995 |title=Inorganic chemistry of main group elements|location=New York |publisher=Wiley-VCH |page=289}}</ref><ref name=Greenwood957>Greenwood and Earnshaw, p. 957</ref> but have some of the physical properties of ''d'' block transition metals.<ref name=Greenwood947>Greenwood and Earnshaw, p. 947</ref> In fact, the metals all the way up to group 6 are united by being class-A cations ([[HSAB theory|"hard" acids]]) that form more stable complexes with ligands whose donor atoms are the most electronegative nonmetals nitrogen, oxygen, and fluorine; metals later in the table form a transition to class-B cations ("soft" acids) that form more stable complexes with ligands whose donor atoms are the less electronegative heavier elements of groups 15 through 17.<ref>Greenwood and Earnshaw, p. 909</ref>

Meanwhile, lutetium behaves chemically as a lanthanide (with which it is often classified) but shows a mix of lanthanide and transition metal physical properties (as does yttrium).<ref>{{cite book |last1=Spedding |first1=F. H. |last2=Beadry |first2=B. J. |editor-last=Hampel |editor-first=C. A. |title=The Encyclopedia of the Chemical Elements |chapter-url=https://archive.org/details/encyclopediaofch00hamp |chapter-url-access=registration |publisher=Reinhold Book Corporation |date=1968 |pages=[https://archive.org/details/encyclopediaofch00hamp/page/374 374–78] |chapter=Lutetium}}</ref><ref>{{cite journal| last1 = Settouti | first1 = N.| last2 = Aourag | first2 = H. | date = 2014| title = A Study of the Physical and Mechanical Properties of Lutetium Compared with Those of Transition Metals: A Data Mining Approach| journal = JOM| volume = 67| issue = 1| pages = 87–93| doi = 10.1007/s11837-014-1247-x| bibcode = 2015JOM....67a..87S| s2cid = 136782659| url = https://www.semanticscholar.org/paper/54dbfdaead5d96c65fe32381422b8cd0927c1ddd}}</ref> Lawrencium, as an analogue of lutetium, would presumably display like characteristics.{{#tag:ref|While Lr is thought to have a p rather than d electron in its ground-state electron configuration, and would therefore be expected to be a volatile metal capable of forming a +1 cation in solution like thallium, no evidence of either of these properties has been able to be obtained despite experimental attempts to do so.<ref name=Silva1642>{{cite book|doi=10.1007/978-94-007-0211-0_13|title=The Chemistry of the Actinide and Transactinide Elements|url=https://archive.org/details/chemistryactinid00mors|url-access=limited|pages=[https://archive.org/details/chemistryactinid00mors/page/n1639 1621–51]|date=2011|isbn=978-94-007-0210-3|publisher=Springer |place=Netherlands|author=Silva, Robert J.|editor= Morss, Lester R.|editor2= Edelstein, Norman M.|editor3= Fuger, Jean |chapter=Chapter 13. Fermium, Mendelevium, Nobelium, and Lawrencium}}</ref> It was originally expected to have a d electron in its electron configuration<ref name=Silva1642/> and this may still be the case for metallic lawrencium, whereas gas phase atomic lawrencium is very likely thought to have a p electron.<ref name=Sato>{{cite journal |last1=Sato |first1=T. K. |last2=Asai |first2=M. |first3=A. |last3=Borschevsky |first4=T. |last4=Stora |first5=N. |last5=Sato |first6=Y. |last6=Kaneya |first7=K. |last7=Tsukada |first8=Ch. E. |last8=Düllman |first9=K. |last9=Eberhardt |first10=E. |last10=Eliav |first11=S. |last11=Ichikawa |first12=U. |last12=Kaldor |first13=J. V. |last13=Kratz |first14=S. |last14=Miyashita |first15=Y. |last15=Nagame |first16=K. |last16=Ooe |first17=A. |last17=Osa |first18=D. |last18=Renisch |first19=J. |last19=Runke |first20=M. |last20=Schädel |first21=P. |last21=Thörle-Pospiech |first22=A. |last22=Toyoshima |first23=N. |last23=Trautmann |date=9 April 2015 |title=Measurement of the first ionization potential of lawrencium, element 103 |journal=Nature |volume=520 |issue=7546 |pages=209–11 |doi=10.1038/nature14342 |pmid=25855457 |bibcode=2015Natur.520..209S |s2cid=4384213 |url=http://cds.cern.ch/record/2008656/files/TKSato-Lr-IP_prep_nature.pdf |access-date=25 October 2017 |archive-url=https://web.archive.org/web/20181030071405/http://cds.cern.ch/record/2008656/files/TKSato-Lr-IP_prep_nature.pdf |archive-date=30 October 2018 |url-status=live }}</ref>|group=n}} The coinage metals in group 11 (copper, silver, and gold) are chemically capable of acting as either transition metals or main group metals.<ref>{{cite book |last=Steele |first=D. |title=The Chemistry of the Metallic Elements |publisher= Pergamon Press |location=Oxford |page=67}}</ref> The volatile group 12 metals, zinc, cadmium and mercury are sometimes regarded as linking the ''d'' block to the ''p'' block. Notionally they are ''d'' block elements but they have few transition metal properties and are more like their ''p'' block neighbors in group 13.<ref>{{cite book |last1=Greenwood|first1=N. N.|last2=Earnshaw|first2=A.|title=Chemistry of the Elements |year=2001|publisher=Elsevier Science Ltd.|location=Oxford|edition=2nd|page=1206|isbn=978-0-7506-3365-9}}</ref><ref>{{cite book |last1=MacKay |first1=K. M.|last2=MacKay |first2=R. A. |last3=Henderson |first3=W. |date=2002 |title=Introduction to Modern Inorganic Chemistry|edition=6th|publisher =Nelson Thornes |location=Cheltenham |isbn=978-0-7487-6420-4 |pages=194–96, 385}}</ref> The relatively inert noble gases, in group 18, bridge the most reactive groups of elements in the periodic table—the halogens in group 17 and the alkali metals in group 1.<ref name="MacKay"/>

===Oxidation number===

With some minor exceptions, [[oxidation number]]s among the elements show four main trends according to their periodic table geographic location: left; middle; right; and south. On the left (groups 1 to 4, not including the f-block elements, and also niobium, tantalum, and probably dubnium in group 5), the highest most stable oxidation number is the group number, with lower oxidation states being less stable. In the middle (groups 3 to 11), higher oxidation states become more stable going down each group. Group 12 is an exception to this trend; they behave as if they were located on the left side of the table. On the right, higher oxidation states tend to become less stable going down a group.<ref name=Fernelius>{{cite journal |last1= Fernelius |first1=W. |last2=C. |title= Some reflections on the periodic table and its use|journal= Journal of Chemical Education |volume=63 |issue= 3|pages=263–66 |doi=10.1021/ed063p263|year=1986 |bibcode=1986JChEd..63..263F }}</ref> The shift between these trends is continuous: for example, group 3 also has lower oxidation states most stable in its lightest member (scandium, with CsScCl3 for example known in the +2 state),<ref name="MeyerCorbett1981">{{cite journal|last1=Meyer|first1=Gerd|last2=Corbett|first2=John D.|title=Reduced ternary halides of scandium: RbScX3 (X = chlorine, bromine) and CsScX3 (X = chlorine, bromine, iodine)|journal=Inorganic Chemistry|volume=20|issue=8|year=1981|pages=2627–31|issn=0020-1669|doi=10.1021/ic50222a047}}</ref> and group 12 is predicted to have [[copernicium]] more readily showing oxidation states above +2.

The lanthanides positioned along the south of the table are distinguished by having the +3 oxidation state in common; this is their most stable state. The early actinides show a pattern of oxidation states somewhat similar to those of their period 6 and 7 transition metal congeners; the later actinides are more similar to the lanthanides, though the last ones (excluding lawrencium) have an increasingly important +2 oxidation state that becomes the most stable state for nobelium.<ref>{{cite book |last1=Wiberg|first1=N.|title= Inorganic Chemistry|year=2001|pages=1644–45|publisher=Academic Press

|isbn=978-0-12-352651-9|location=San Diego}}</ref>

===Primogenic symmetry===

The 1s, 2p, 3d, and 4f shells are each the first to have their value of ℓ, the [[azimuthal quantum number]] that determines a subshell's orbital angular momentum. This gives them some special properties,<ref name=Kaupp>{{cite journal |last=Kaupp |first=Martin |date=1 December 2006 |title=The role of radial nodes of atomic orbitals for chemical bonding and the periodic table |url=https://pdfs.semanticscholar.org/b624/3805138ab8701ce5b4aa580f626992ff2fde.pdf |journal=Journal of Computational Chemistry |volume=28 |issue=1 |pages=320–25 |doi=10.1002/jcc.20522 |pmid=17143872 |s2cid=12677737 |access-date=7 February 2018}}</ref> a phenomenon referred to in the West as ''priomgenic symmetry'' and in Russian literature, as ''kainosymmetry'' (from Greek καινός "new").<ref name=Imyanitov>{{cite journal |last1=Imyanitov |first1=N. S. |date=2011 |title=Application of a new formulation of the periodic law to predicting the proton affinity of elements |journal=Russian Journal of Inorganic Chemistry |volume=56 |issue=5 |pages=745–48 |doi=10.1134/S003602361105010X|s2cid=98328428 }}</ref><ref name=primefan>

{{cite web |url=http://www.primefan.ru/stuff/personal/ptable.pdf |title=Периодическая система химических элементов Д. И. Менделеева |trans-title=D. I. Mendeleev's periodic system of the chemical elements |last=Kulsha |first=Andrey |date=2004 |website=primefan.ru |access-date=17 May 2020 |language=ru}}</ref> Elements filling these orbitals are usually less metallic than their heavier homologues, prefer lower oxidation states, and have smaller atomic and ionic radii. As primogenic orbitals appear in the even rows (except for 1s), this creates an even–odd difference between periods from period 2 onwards: elements in even periods are smaller and have more oxidising higher oxidation states (if they exist), whereas elements in odd periods differ in the opposite direction.<ref name=primefan/>

==History==