Editing Periodic table (section)

==Structure<span class="anchor" id="Detailed table"></span> ==
{{Periodic table}}

[[File:Atomic-orbital-clouds spdf m0.png|thumb|upright=1.5|3D views of some [[Hydrogen-like atom|hydrogen-like]] [[atomic orbital]]s showing probability density and phase (g orbitals and higher are not shown)]]
Each chemical element has a unique [[atomic number]] (''Z''{{--}} for "Zahl", German for "number") representing the number of [[proton]]s in its [[atomic nucleus|nucleus]].<ref name="neutronium">An [[neutronium|element zero]] (i.e. a substance composed purely of neutrons), is included in a few alternate presentations, for example, in the [https://www.meta-synthesis.com/webbook/35_pt/pt_database.php?PT_id=22 Chemical Galaxy]. See {{cite journal |last=Labarca |first=M. |title=An element of atomic number zero? |journal=New Journal of Chemistry |year=2016 |volume=40|issue=11|pages=9002–9006 |doi=10.1039/C6NJ02076C|hdl=11336/46854 |hdl-access=free  |issn=1144-0546 }}</ref> Each distinct atomic number therefore corresponds to a class of atom: these classes are called the [[chemical element]]s.<ref>{{GoldBookRef |title=Chemical element |file=C01022}}</ref> The chemical elements are what the periodic table classifies and organizes. [[Hydrogen]] is the element with atomic number 1; [[helium]], atomic number 2; [[lithium]], atomic number 3; and so on. Each of these names can be further abbreviated by a one- or two-letter [[chemical symbol]]; those for hydrogen, helium, and lithium are respectively H, He, and Li.<ref name="IUPAC-redbook"/> Neutrons do not affect the atom's chemical identity, but do affect its weight. Atoms with the same number of protons but different numbers of neutrons are called [[isotope]]s of the same chemical element.<ref name="IUPAC-redbook" /> Naturally occurring elements usually occur as mixes of different isotopes; since each isotope usually occurs with a characteristic abundance, naturally occurring elements have well-defined [[atomic weight]]s, defined as the average mass of a naturally occurring atom of that element.<ref name="ciaaw">{{cite web |title=Standard Atomic Weights |website=Commission on Isotopic Abundances and Atomic Weights |date=2019 |publisher=International Union of Pure and Applied Chemistry |url=https://www.ciaaw.org/atomic-weights.htm |access-date=7 February 2021 |url-status=live |archive-date=8 August 2020 |archive-url=https://web.archive.org/web/20200808155924/https://www.ciaaw.org/atomic-weights.htm}}</ref>
All elements have multiple [[isotope]]s, variants with the same number of protons but different numbers of [[neutron]]s. For example, [[carbon]] has three naturally occurring isotopes: all of its [[atom]]s have six protons and most have six neutrons as well, but about one per cent have seven neutrons, and a very small fraction have eight neutrons. Isotopes are never separated in the periodic table; they are always grouped together under a single element. When atomic mass is shown, it is usually the weighted average of naturally occurring isotopes; but if no isotopes occur naturally in significant quantities, the mass of the most stable isotope usually appears, often in parentheses.<ref name="Greenwood">Greenwood & Earnshaw, pp. 24–27</ref>

In the standard periodic table, the elements are listed in order of increasing atomic number. A new row ([[Period (periodic table)|''period'']]) is started when a new [[electron shell]] has its first [[electron]]. Columns ([[Group (periodic table)|''groups'']]) are determined by the [[electron configuration]] of the atom; elements with the same number of electrons in a particular subshell fall into the same columns (e.g. [[oxygen]], [[sulfur]], and [[selenium]] are in the same column because they all have four electrons in the outermost p-subshell). Elements with similar chemical properties generally fall into the same group in the periodic table, although in the f-block, and to some respect in the d-block, the elements in the same period tend to have similar properties, as well. Thus, it is relatively easy to predict the chemical properties of an element if one knows the properties of the elements around it.<ref>Gray, p. 6</ref>

Today, 118 elements are known, the first 94 of which are known to occur naturally on Earth at present.<ref name=ThorntonBurdette/>{{efn|The question of how many natural elements there are is quite complicated and is not fully resolved. The heaviest element that occurs in large quantities on Earth is element 92, [[uranium]]. However, uranium can undergo [[spontaneous fission]] in nature, and the resulting neutrons can strike other uranium atoms. If neutron capture then occurs, elements 93 and 94, [[neptunium]] and [[plutonium]], are formed via [[beta decay]];<ref name=ThorntonBurdette/> these are in fact more common than some of the rarest elements in the first 92, such as [[promethium]], [[astatine]], and [[francium]] (see [[Abundance of elements in Earth's crust]]). Theoretically, neutron capture on the resulting plutonium might produce even higher-numbered elements, but the quantities would be too small to be observed.<ref name=ThorntonBurdette/> In the early Solar System, shorter-lived elements had not yet decayed away, and consequently there were more than 94 naturally occurring elements. [[Curium]] (element 96) is the longest-lived element beyond the first 94, and is probably still being brought to Earth via [[cosmic ray]]s, but it has not been found.<ref name=ThorntonBurdette>{{cite journal |last1=Thornton |first1=Brett F. |last2=Burdette |first2=Shawn C. |date=2019 |title=Neutron stardust and the elements of Earth |url=https://www.nature.com/articles/s41557-018-0190-9 |journal=Nature Chemistry |volume=11 |issue=1 |pages=4–10 |doi=10.1038/s41557-018-0190-9 |pmid=30552435 |bibcode=2019NatCh..11....4T |s2cid=54632815 |access-date=19 February 2022 |archive-date=14 August 2021 |archive-url=https://web.archive.org/web/20210814111535/https://www.nature.com/articles/s41557-018-0190-9 |url-status=live |url-access=subscription }}</ref> Elements up to 99 ([[einsteinium]]) have been observed in [[Przybylski's Star]].<ref name=gopka08>{{cite journal |last1=Gopka |first1=V.F. |last2=Yushchenko |first2=A.V. |last3=Yushchenko |first3=V.A. |last4=Panov |first4=I.V. |last5=Kim |first5=Ch. |date=15 May 2008 |title=Identification of absorption lines of short half-life actinides in the spectrum of Przybylski's star (HD 101065) |journal=Kinematics and Physics of Celestial Bodies |volume=24 |issue=2 |pages=89–98 |doi=10.3103/S0884591308020049 |bibcode = 2008KPCB...24...89G |s2cid=120526363 }}</ref> Elements up to 100 ([[fermium]]) probably occurred in the [[natural nuclear fission reactor]] at [[Oklo Mine]], [[Gabon]], but they have long since decayed away.<ref name="emsley">{{cite book |last=Emsley |first=John |date=2011 |title=Nature's Building Blocks: An A-Z guide to the elements |edition=New |publisher=Oxford University Press |location=New York, NY |isbn=978-0-19-960563-7}}</ref> Even heavier elements may be produced in the [[r-process]] via [[supernova]]e or [[neutron star merger]]s, but this has not been confirmed. It is not clear how far they would extend past 100 and how long they would last: calculations suggest that nuclides of mass number around 280 to 290 are formed in the r-process, but quickly [[beta decay]] to nuclides that suffer [[spontaneous fission]], so that 99.9% of the produced [[superheavy element|superheavy]] nuclides would decay within a month.<ref>{{cite journal |last1=Panov |first1=I.V. |date=2017 |title=Formation of Superheavy Elements in Nature |journal=Physics of Atomic Nuclei |volume=81 |issue=1 |pages=57–65 |doi=10.1134/S1063778818010167|s2cid=125149409 }}</ref> If instead they were sufficiently long-lived, they might similarly be brought to Earth via cosmic rays, but again none have been found.<ref name=ThorntonBurdette/>|name=transuranium}} The remaining 24, americium to oganesson (95–118), occur only when synthesized in laboratories. Of the 94 naturally occurring elements, 83 are [[primordial element|primordial]] and 11 occur only in decay chains of primordial elements. A few of the latter are so rare that they were not discovered in nature, but were synthesized in the laboratory before it was determined that they do exist in nature after all: [[technetium]] (element 43), [[promethium]] (element 61), [[astatine]] (element 85), [[neptunium]] (element 93), and [[plutonium]] (element 94).<ref name="emsley"/> No element heavier than [[einsteinium]] (element 99) has ever been observed in macroscopic quantities in its pure form, nor has [[astatine]]; [[francium]] (element 87) has been only photographed in the form of [[light]] emitted from microscopic quantities (300,000 atoms).<ref>{{cite book| title = The Chemistry of the Actinide and Transactinide Elements| editor1-last = Morss| editor1-first=L. R.|editor2-first = N. M.|editor2-last = Edelstein| editor3-last = Fuger|editor3-first = J.| last = Silva|first = Robert J.| chapter = Fermium, Mendelevium, Nobelium and Lawrencium| publisher = [[Springer Science+Business Media]]| year = 2006| isbn = 978-1-4020-3555-5| location = Dordrecht| edition = 3rd| ref = CITEREFHaire2006}}</ref> Of the 94 natural elements, eighty have a stable isotope and one more ([[bismuth]]) has an almost-stable isotope (with a [[half-life]] of 2.01×10<sup>19</sup>&nbsp;years, over a billion times the [[age of the universe]]).<ref name=Bi209alpha2>{{cite journal | last = Marcillac | first = Pierre de |author2=Noël Coron |author3=Gérard Dambier |author4=Jacques Leblanc |author5=Jean-Pierre Moalic |date=April 2003 | title = Experimental detection of α-particles from the radioactive decay of natural bismuth | journal = Nature | volume = 422 | pages = 876–878 | doi = 10.1038/nature01541 | pmid = 12712201 | issue = 6934 | bibcode=2003Natur.422..876D| s2cid = 4415582 }}</ref>{{efn|Some isotopes currently considered stable are theoretically expected to be radioactive with extremely long half-lives: for instance, all the stable isotopes of elements 62 ([[samarium]]), 63 ([[europium]]), and all elements from 67 ([[holmium]]) onward are expected to undergo [[alpha decay]] or [[double beta decay]]. However, the predicted half-lives are extremely long (e.g. the alpha decay of <sup>208</sup>Pb to the ground state of <sup>204</sup>Hg is expected to have a half-life greater than 10<sup>120</sup> years), and the decays have never been observed.<ref name="bellidecay">{{cite journal |last1=Belli |first1=P. |last2=Bernabei |first2=R. |last3=Danevich |first3=F. A. |last4=Incicchitti |first4=A. |last5=Tretyak |first5=V. I. |display-authors=3 |title=Experimental searches for rare alpha and beta decays |journal=European Physical Journal A |date=2019 |volume=55 |issue=8 |pages=140–1–140–7 |doi=10.1140/epja/i2019-12823-2 |issn=1434-601X |arxiv=1908.11458|bibcode=2019EPJA...55..140B |s2cid=201664098 }}</ref><ref name="Tretyak2002">{{Cite journal

 |last1=Tretyak |first1=V.I. 
 |last2=Zdesenko |first2=Yu.G. 
 |year=2002
 |title=Tables of Double Beta Decay Data — An Update
 |journal=[[At. Data Nucl. Data Tables]] |volume=80 |issue=1 |pages=83–116
 |doi=10.1006/adnd.2001.0873
|bibcode=2002ADNDT..80...83T }}</ref>}} Two more, [[thorium]] and [[uranium]], have isotopes undergoing [[radioactive decay]] with a half-life comparable to the [[age of the Earth]]. The stable elements plus bismuth, thorium, and uranium make up the 83 [[primordial nuclide|primordial]] elements that survived from the Earth's formation.{{efn|The half-life of [[plutonium]]'s most stable isotope is just long enough that it should also be a primordial element. A 1971 study claimed to have detected primordial plutonium,<ref name="PU244">{{cite journal |first1=D. C. |last1=Hoffman |first2=F. O. |last2=Lawrence |first3=J. L. |last3=Mewherter |first4=F. M. |last4=Rourke |title=Detection of Plutonium-244 in Nature
 |journal=[[Nature (journal)|Nature]] |volume=234 |pages= 132–134 |year=1971 |doi=10.1038/234132a0|bibcode = 1971Natur.234..132H |issue=5325|s2cid=4283169 }}</ref> but a more recent study from 2012 could not detect it.<ref name="PRC">{{cite journal|last=Lachner|first=J.|display-authors=etal|date=2012|title=Attempt to detect primordial <sup>244</sup>Pu on Earth|journal=Physical Review C|volume=85|issue=1|page=015801| doi=10.1103/PhysRevC.85.015801|bibcode=2012PhRvC..85a5801L}}</ref> Based on its likely initial abundance in the Solar System, present experiments as of 2022 are likely about an order of magnitude away from detecting live primordial <sup>244</sup>Pu.<ref>{{cite journal |last1=Wu |first1=Yang |last2=Dai |first2=Xiongxin |first3=Shan |last3=Xing |first4=Maoyi |last4=Luo |first5=Marcus |last5=Christl |first6=Hans-Arno |last6=Synal |first7=Shaochun |last7=Hou |date=2022 |title=Direct search for primordial <sup>244</sup>Pu in Bayan Obo bastnaesite |url=http://www.ccspublishing.org.cn/article/doi/10.1016/j.cclet.2022.03.036?pageType=en |journal=Chinese Chemical Letters |volume=33 |issue=7 |pages=3522–3526 |doi=10.1016/j.cclet.2022.03.036 |s2cid=247443809 |access-date=29 January 2024|url-access=subscription }}</ref>}} The remaining eleven natural elements decay quickly enough that their continued trace occurrence rests primarily on being constantly regenerated as intermediate products of the decay of thorium and uranium.{{efn|Tiny traces of plutonium are also continually brought to Earth via cosmic rays.<ref name="WallnerFaestermann2015">{{cite journal |last1=Wallner |first1=A. |last2=Faestermann |first2=T. |last3=Feige |first3=J. |last4=Feldstein |first4=C. |last5=Knie |first5=K. |last6=Korschinek |first6=G. |last7=Kutschera |first7=W. |last8=Ofan |first8=A. |last9=Paul |first9=M. |last10=Quinto |first10=F. |last11=Rugel |first11=G. |last12=Steier |first12=P. |display-authors=6 |year=2015 |title=Abundance of live {{sup|244}}Pu in deep-sea reservoirs on Earth points to rarity of actinide nucleosynthesis |journal=Nature Communications |volume=6 |page=5956 |issn=2041-1723|doi=10.1038/ncomms6956|pmid=25601158 |pmc=4309418 |arxiv=1509.08054|bibcode=2015NatCo...6.5956W}}</ref>}} All 24 known artificial elements are radioactive.<ref name="IUPAC-redbook" />

=== Group names and numbers ===
Under an international naming convention, the groups are numbered numerically from 1 to 18 from the leftmost column (the alkali metals) to the rightmost column (the noble gases). The f-block groups are ignored in this numbering.<ref name="IUPAC">{{cite book|title=Nomenclature of Inorganic Chemistry: IUPAC Recommendations 2005|last1=Connelly|first1=N. G.|last2=Damhus|first2=T.|last3=Hartshorn|first3=R. M.|last4=Hutton|first4=A. T.|year=2005|publisher=RSC Publishing|isbn=978-0-85404-438-2|page=51|url=https://old.iupac.org/publications/books/rbook/Red_Book_2005.pdf|access-date=26 November 2018|archive-url=https://web.archive.org/web/20181123034019/https://old.iupac.org/publications/books/rbook/Red_Book_2005.pdf|archive-date=23 November 2018|url-status=live}}</ref> Groups can also be named by their first element, e.g. the "scandium group" for group 3.<ref name="IUPAC"/> Previously, groups were known by [[Roman numerals]]. In the United States, the Roman numerals were followed by either an "A" if the group was in the [[s-block|s-]] or [[p-block]], or a "B" if the group was in the [[d-block]]. The Roman numerals used correspond to the last digit of today's naming convention (e.g. the [[group 4 element]]s were group IVB, and the [[Carbon group|group 14 elements]] were group IVA). In Europe, the lettering was similar, except that "A" was used for groups 1 through 7, and "B" was used for groups 11 through 17. In addition, groups 8, 9 and 10 used to be treated as one triple-sized group, known collectively in both notations as group VIII. In 1988, the new [[IUPAC]] (International Union of Pure and Applied Chemistry) naming system (1–18) was put into use, and the old group names (I–VIII) were deprecated.<ref name="Fluck">{{cite journal |last1=Fluck |first1=E. |year=1988 |title=New Notations in the Periodic Table |journal=[[Pure and Applied Chemistry|Pure Appl. Chem.]] |volume=60 |pages=431–436|doi=10.1351/pac198860030431 |url=https://www.iupac.org/publications/pac/1988/pdf/6003x0431.pdf |access-date=24 March 2012 |issue=3 |s2cid=96704008 |url-status=live |archive-url=https://web.archive.org/web/20120325152951/https://www.iupac.org/publications/pac/1988/pdf/6003x0431.pdf |archive-date=25 March 2012}}</ref>

{{Periodic table (group names)}}

=== Presentation forms<span class="anchor" id="The long- or 32-column table"></span> ===
<div style="border:1px solid grey; float:right; text-align:center; padding:0.2em; margin:0; font-size:90%;">
{{Periodic table (32 columns, micro)}}
32 columns
{{Periodic table (18 columns, micro)}}
18 columns
</div>
For reasons of space,<ref name=Petrucci331/><ref>{{cite journal |last1=Pfeiffer |first1=Paul |date=1920 |title=Die Befruchtung der Chemie durch die Röntgenstrahlenphysik |url=https://link.springer.com/article/10.1007/BF02448807 |journal=Naturwissenschaften |language=de |volume=8 |issue=50 |pages=984–991 |bibcode=1920NW......8..984P |doi=10.1007/BF02448807 |s2cid=7071495}}</ref> the periodic table is commonly presented with the f-block elements cut out and positioned as a distinct part below the main body.<ref name="cartoon" /><ref name="Petrucci331" /><ref name="Fluck" /> This reduces the number of element columns from 32 to 18.<ref name=Petrucci331/>

Both forms represent the same periodic table.<ref name="IUPAC-redbook" /> The form with the f-block included in the main body is sometimes called the 32-column<ref name="IUPAC-redbook" /> or long form;<ref name="Thyssen" /> the form with the f-block cut out the 18-column<ref name="IUPAC-redbook" /> or medium-long form.<ref name="Thyssen" /> The 32-column form has the advantage of showing all elements in their correct sequence, but it has the disadvantage of requiring more space.<ref>Scerri, p. 375</ref> The form chosen is an editorial choice, and does not imply any change of scientific claim or statement. For example, when discussing [[Group 3 element#Composition|the composition of group 3]], the options can be shown equally (unprejudiced) in both forms.<ref name="2015IUPAC">{{cite web|url=https://iupac.org/projects/project-details/?project_nr=2015-039-2-200|title=The constitution of group 3 of the periodic table|publisher=IUPAC|access-date=30 July 2016|date=2015|url-status=live|archive-url=https://web.archive.org/web/20160705053631/https://iupac.org/projects/project-details/?project_nr=2015-039-2-200|archive-date=5 July 2016}}</ref>

Periodic tables usually at least show the elements' symbols; many also provide supplementary information about the elements, either via colour-coding or as data in the cells. The above table shows the names and atomic numbers of the elements, and also their blocks, natural occurrences and [[standard atomic weight]]s. For the short-lived elements without standard atomic weights, the mass number of the most stable known isotope is used instead. Other tables may include properties such as state of matter, melting and boiling points, densities, as well as provide different classifications of the elements.{{efn|See for example [https://www.sigmaaldrich.com/SG/en/product/aldrich/z543209 the periodic table poster sold by Sigma-Aldrich.]}}
=== Electron configurations ===

{{main|Electron configuration}}

The periodic table is a graphic description of the periodic law,<ref name="Scerri17"/> which states that the properties and atomic structures of the chemical elements are a [[periodic function]] of their [[atomic number]].<ref>{{cite Merriam-Webster |periodic law |access-date=29 March 2021}}</ref> Elements are placed in the periodic table according to their [[electron configuration]]s,<ref name="Jensen2009"/> the periodic recurrences of which explain the [[periodic trends|trends]] in properties across the periodic table.<ref name="FIII19" />

An electron can be thought of as inhabiting an [[atomic orbital]], which characterizes the probability it can be found in any particular region around the atom. Their energies are [[quantization (physics)|quantised]], which is to say that they can only take discrete values. Furthermore, electrons obey the [[Pauli exclusion principle]]: different electrons must always be in different states. This allows classification of the possible states an electron can take in various energy levels known as shells, divided into individual subshells, which each contain one or more orbitals. Each orbital can contain up to two electrons: they are distinguished by a quantity known as [[Spin (physics)|spin]], conventionally labelled "up" or "down".<ref>Petrucci et al., p. 323</ref>{{efn|Strictly speaking, one cannot draw an orbital such that the electron is guaranteed to be inside it, but it can be drawn to guarantee a 90% probability of this for example.<ref>Petrucci et al., p. 306</ref>}} In a cold atom (one in its ground state), electrons arrange themselves in such a way that the total energy they have is minimized by occupying the lowest-energy orbitals available.<ref>Petrucci et al., p. 322</ref> Only the outermost electrons (so-called [[valence electron]]s) have enough energy to break free of the nucleus and participate in chemical reactions with other atoms. The others are called [[core electron]]s.<ref>{{cite book |last1=Ball |first1=David W. |last2=Key |first2=Jessie A. |date=2011 |title=Introductory Chemistry |edition=1st Canadian |place=Vancouver, British Columbia |publisher=BC Campus (opentextbc.ca) |isbn=978-1-77420-003-2 |url=https://opentextbc.ca/introductorychemistry/chapter/electronic-structure-and-the-periodic-table/ |access-date=15 August 2021 |archive-date=15 August 2021 |archive-url=https://web.archive.org/web/20210815072718/https://opentextbc.ca/introductorychemistry/chapter/electronic-structure-and-the-periodic-table/ |url-status=live |page=}}</ref>

{| class="wikitable" style="float:right; margin:0.5em; text-align:center;"
! style="text-align:right;" |ℓ =
! 0
! 1
! 2
! 3
! 4
! 5
! 6
! rowspan=2 | Shell capacity  (2''n''<sup>2</sup>)<ref>{{cite web |date=6 May 2020 |title=Electron Configurations |url=https://www.chem.fsu.edu/chemlab/chm1045/e_config.html |access-date=17 April 2022 |website=www.chem.fsu.edu |publisher=Florida State University |archive-date=6 May 2022 |archive-url=https://web.archive.org/web/20220506074340/https://www.chem.fsu.edu/chemlab/chm1045/e_config.html |url-status=live }}</ref>
|-
! style="text-align:right;" | Orbital
! s
! p
! d
! f
! g
! h
! i
|-
! ''n'' = 1
| bgcolor="{{element color|s-block}}" | 1s
| colspan=6 |
| 2
|-
! ''n'' = 2
| bgcolor="{{element color|s-block}}" | 2s
| bgcolor="{{element color|p-block}}" | 2p
| colspan=5 |
| 8
|-
! ''n'' = 3
| bgcolor="{{element color|s-block}}" | 3s
| bgcolor="{{element color|p-block}}" | 3p
| bgcolor="{{element color|d-block}}" | 3d
| colspan=4 |
| 18
|-
! ''n'' = 4
| bgcolor="{{element color|s-block}}" | 4s
| bgcolor="{{element color|p-block}}" | 4p
| bgcolor="{{element color|d-block}}" | 4d
| bgcolor="{{element color|f-block}}" | 4f
| colspan=3 |
| 32
|-
! ''n'' = 5
| bgcolor="{{element color|s-block}}" | 5s
| bgcolor="{{element color|p-block}}" | 5p
| bgcolor="{{element color|d-block}}" | 5d
| bgcolor="{{element color|f-block}}" | 5f
| bgcolor="{{element color|g-block}}" | 5g
| colspan=2 |
| 50
|-
! ''n'' = 6
| bgcolor="{{element color|s-block}}" | 6s
| bgcolor="{{element color|p-block}}" | 6p
| bgcolor="{{element color|d-block}}" | 6d
| bgcolor="{{element color|f-block}}" | 6f
| bgcolor="{{element color|g-block}}" | 6g
| bgcolor="{{element color|h-block}}" | 6h
|
| 72
|-
! ''n'' = 7
| bgcolor="{{element color|s-block}}" | 7s
| bgcolor="{{element color|p-block}}" | 7p
| bgcolor="{{element color|d-block}}" | 7d
| bgcolor="{{element color|f-block}}" | 7f
| bgcolor="{{element color|g-block}}" | 7g
| bgcolor="{{element color|h-block}}" | 7h
| bgcolor="{{element color|i-block}}" | 7i
| 98
|-
! Subshell capacity (4ℓ+2)
| 2
| 6
| 10
| 14
| 18
| 22
| 26
|
|}
Elements are known with up to the first seven shells occupied. The first shell contains only one orbital, a spherical s orbital. As it is in the first shell, this is called the 1s orbital. This can hold up to two electrons. The second shell similarly contains a 2s orbital, and it also contains three dumbbell-shaped 2p orbitals, and can thus fill up to eight electrons (2×1 + 2×3 = 8). The third shell contains one 3s orbital, three 3p orbitals, and five 3d orbitals, and thus has a capacity of 2×1 + 2×3 + 2×5 = 18. The fourth shell contains one 4s orbital, three 4p orbitals, five 4d orbitals, and seven 4f orbitals, thus leading to a capacity of 2×1 + 2×3 + 2×5 + 2×7 = 32.<ref name="Petrucci331" /> Higher shells contain more types of orbitals that continue the pattern, but such types of orbitals are not filled in the ground states of known elements.<ref name="Goudsmit" /> The subshell types are characterized by the [[quantum number]]s. Four numbers describe an orbital in an atom completely: the [[principal quantum number]] ''n'', the [[azimuthal quantum number]] ℓ (the orbital type), the [[magnetic quantum number|orbital magnetic quantum number]] ''m''<sub>ℓ</sub>, and the [[spin quantum number|spin magnetic quantum number]] ''m<sub>s</sub>''.<ref name="FIII19" />

==== Order of subshell filling ====

[[File:Aufbau Principle-en.svg|thumb|right|192px|Idealized order of subshell filling according to the [[Madelung rule]] ]]
The sequence in which the subshells are filled is given in most cases by the [[Aufbau principle]], also known as the Madelung or Klechkovsky rule (after [[Erwin Madelung]] and [[Vsevolod Klechkovsky]] respectively). This rule was first observed empirically by Madelung, and Klechkovsky and later authors gave it theoretical justification.<ref name=Jolly>{{cite book |last1=Jolly |first1=William L. |title=Modern Inorganic Chemistry |edition=1st |publisher=McGraw-Hill |date=1984 |pages=[https://archive.org/details/trent_0116300649799/page/10 10–12] |isbn=0-07-032760-2 |url=https://archive.org/details/trent_0116300649799/page/10 }}</ref><ref name=Ostrovsky/><ref name=Ostrovsky1981/><ref name=Wong/>{{efn|name=lowdin}} The shells overlap in energies, and the Madelung rule specifies the sequence of filling according to:<ref name="Ostrovsky">{{cite journal |last1=Ostrovsky |first1=V. N. |date=May 2001 |title=What and How Physics Contributes to Understanding the Periodic Law |journal=Foundations of Chemistry |volume=3 |issue=2 |pages=145–181 |doi=10.1023/A:1011476405933 |s2cid=15679915 }}</ref>
:1s ≪ 2s < 2p ≪ 3s < 3p ≪ 4s < 3d < 4p ≪ 5s < 4d < 5p ≪ 6s < 4f < 5d < 6p ≪ 7s < 5f < 6d < 7p ≪ ... <!--write in 8s and 5g when they get discovered-->
Here the sign ≪ means "much less than" as opposed to < meaning just "less than".<ref name="Ostrovsky"/> Phrased differently, electrons enter orbitals in order of increasing ''n'' + ℓ, and if two orbitals are available with the same value of ''n'' + ℓ, the one with lower ''n'' is occupied first.<ref name="Goudsmit" /><ref name="Wong">{{cite journal |title=Theoretical justification of Madelung's rule |journal=[[Journal of Chemical Education|J. Chem. Educ.]] |last=Wong |first=D. Pan |date=1979 |issue=11 |pages=714–718 |volume=56 |doi=10.1021/ed056p714 |bibcode = 1979JChEd..56..714W }}</ref> In general, orbitals with the same value of ''n'' + ℓ are similar in energy, but in the case of the s&nbsp;orbitals (with ℓ = 0), quantum effects raise their energy to approach that of the next ''n'' + ℓ group. Hence the periodic table is usually drawn to begin each row (often called a period) with the filling of a new s&nbsp;orbital, which corresponds to the beginning of a new shell.<ref name=Ostrovsky/><ref name=Ostrovsky1981>{{cite journal |last1=Ostrovsky |first1=V. N. |date=1981 |title=Dynamic symmetry of atomic potential |url= |journal=Journal of Physics B: Atomic and Molecular Physics |volume=14 |issue=23 |pages=4425–4439 |doi=10.1088/0022-3700/14/23/008 |bibcode=1981JPhB...14.4425O }}</ref><ref name="Petrucci331" /> Thus, with the exception of the first row, each period length appears twice:<ref name=Ostrovsky/>
:2, 8, 8, 18, 18, 32, 32, ...

The overlaps get quite close at the point where the d&nbsp;orbitals enter the picture,<ref name="Petrucci328"/> and the order can shift slightly with atomic number<ref name=Cao/> and atomic charge.<ref name="Jorgensen"/>{{efn|
Once two to four electrons are removed, the d and f orbitals usually become lower in energy than the s ones:<ref name="Jorgensen"/>
:1s ≪ 2s < 2p ≪ 3s < 3p ≪ 3d < 4s < 4p ≪ 4d < 5s < 5p ≪ 4f < 5d < 6s < 6p ≪ 5f < 6d < 7s < 7p ≪ ...

and in the limit for extremely highly charged ions, orbitals simply fill in the order of increasing ''n'' instead. There is a gradual transition between the limiting situations of highly charged ions (increasing ''n'') and neutral atoms (Madelung's rule).<ref name="Goudsmit"/> Thus for example, the energy order for the 55th electron outside the xenon core proceeds as follows in the isoelectronic series of caesium (55 electrons):<ref name=elyashevich/>
:Cs<sup>0</sup>: 6s < 6p < 5d < 7s < 4f
:Ba<sup>+</sup>: 6s < 5d < 6p < 7s < 4f
:La<sup>2+</sup>: 5d < 4f < 6s < 6p < 7s
:Ce<sup>3+</sup>: 4f < 5d < 6s < 6p < 7s
and in the isoelectronic series of holmium (67 electrons), a Ho<sup>0</sup> atom is [Xe]4f<sup>11</sup>6s<sup>2</sup>, but Er<sup>+</sup> is [Xe]4f<sup>12</sup>6s<sup>1</sup>, Tm<sup>2+</sup> through W<sup>7+</sup> are [Xe]4f<sup>13</sup>, and from Re<sup>8+</sup> onward the configuration is [Cd]4f<sup>14</sup>5p<sup>5</sup> following the hydrogenic order.<ref name=rareearths/><ref>{{cite web |url=https://physics.nist.gov/cgi-bin/ASD/ie.pl?spectra=Ho-like&submit=Retrieve+Data&units=1&format=0&order=0&at_num_out=on&sp_name_out=on&ion_charge_out=on&el_name_out=on&seq_out=on&shells_out=on&level_out=on&ion_conf_out=on&e_out=0&unc_out=on&biblio=on |title=NIST Atomic Spectra Database: Ionization Energies Data: All Ho-like |author=NIST |date=2023 |website=nist.gov |publisher=NIST |access-date=5 January 2024 |quote=}}</ref>
:
Also, the ordering of the orbitals between each ≪ changes somewhat throughout each period. For example, the ordering in argon and potassium is 3p ≪ 4s < 4p ≪ 3d; by calcium it has become 3p ≪ 4s < 3d < 4p; from scandium to copper it is 3p ≪ 3d < 4s < 4p; and from zinc to krypton it is 3p < 3d ≪ 4s < 4p<ref name=Cao>{{cite journal |last1=Cao |first1=Changsu |last2=Vernon |first2=René E. |first3=W. H. Eugen |last3=Schwarz |first4=Jun |last4=Li |date=6 January 2021 |title=Understanding Periodic and Non-periodic Chemistry in Periodic Tables |journal=Frontiers in Chemistry |volume=8 |issue=813 |page=813 |doi=10.3389/fchem.2020.00813 |pmid=33490030 |pmc=7818537 |bibcode=2021FrCh....8..813S |doi-access=free }}</ref> as the d&nbsp;orbitals fall into the core at gallium.<ref>{{cite journal |last1=Tossell |first1=J.A. |date=1 November 1977 |title=Theoretical studies of valence orbital binding energies in solid zinc sulfide, zinc oxide, and zinc fluoride |journal=Inorganic Chemistry |volume=16 |issue=11 |pages=2944–2949 |doi=10.1021/ic50177a056}}</ref><ref name=KW/> Deeply buried core shells in heavy atoms thus come closer to the hydrogenic order: around osmium (''Z'' {{=}} 76) 4f falls below 5p, and around bismuth (''Z'' {{=}} 83) 4f falls below 5s as well.<ref name=rareearths/>
}}

Starting from the simplest atom, this lets us build up the periodic table one at a time in order of atomic number, by considering the cases of single atoms. In [[hydrogen]], there is only one electron, which must go in the lowest-energy orbital 1s. This [[electron configuration]] is written 1s<sup>1</sup>, where the superscript indicates the number of electrons in the subshell. [[Helium]] adds a second electron, which also goes into 1s, completely filling the first shell and giving the configuration 1s<sup>2</sup>.<ref name="FIII19">{{cite book |last1=Feynman |first1=Richard |last2=Leighton |first2=Robert B. |last3=Sands |first3=Matthew |date=1964 |title=The Feynman Lectures on Physics |url=https://feynmanlectures.caltech.edu/III_19.html |publisher=Addison–Wesley |volume=3 |chapter=19. The Hydrogen Atom and The Periodic Table |isbn=0-201-02115-3 |access-date=15 August 2021 |archive-date=19 October 2021 |archive-url=https://web.archive.org/web/20211019202245/https://www.feynmanlectures.caltech.edu/III_19.html |url-status=live }}</ref><ref name=jensenlaw>{{cite web|url=http://www.che.uc.edu/jensen/W.%20B.%20Jensen/Reprints/081.%20Periodic%20Table.pdf|archive-url=https://web.archive.org/web/20201110113324/http://www.che.uc.edu/jensen/W.%20B.%20Jensen/Reprints/081.%20Periodic%20Table.pdf|archive-date=10 November 2020|last1=Jensen|first1=William B.|author-link=William B. Jensen|title=The Periodic Law and Table|date=2000|access-date=10 December 2022}}</ref>{{efn|In fact, electron configurations represent a first-order approximation: an atom really exists in a superposition of multiple configurations, and electrons in an atom are indistinguishable.<ref name=Scerri2009/> The elements in the d- and f-blocks have multiple configurations separated by small energies and can change configuration depending on the chemical environment.<ref name=Jorgensen/> In some of the undiscovered g-block elements, mixing of configurations may become so important that the result can no longer be well-described by a single configuration.<ref name=nefedov/>}}

Starting from the third element, [[lithium]], the first shell is full, so its third electron occupies a 2s orbital, giving a 1s<sup>2</sup> 2s<sup>1</sup> configuration. The 2s electron is lithium's only valence electron, as the 1s subshell is now too tightly bound to the nucleus to participate in chemical bonding to other atoms: such a shell is called a "[[Core electron|core shell]]". The 1s subshell is a core shell for all elements from lithium onward. The 2s subshell is completed by the next element [[beryllium]] (1s<sup>2</sup> 2s<sup>2</sup>). The following elements then proceed to fill the 2p subshell. [[Boron]] (1s<sup>2</sup> 2s<sup>2</sup> 2p<sup>1</sup>) puts its new electron in a 2p orbital; [[carbon]] (1s<sup>2</sup> 2s<sup>2</sup> 2p<sup>2</sup>) fills a second 2p orbital; and with [[nitrogen]] (1s<sup>2</sup> 2s<sup>2</sup> 2p<sup>3</sup>) all three 2p orbitals become singly occupied. This is consistent with [[Hund's rule]], which states that atoms usually prefer to singly occupy each orbital of the same type before filling them with the second electron. [[Oxygen]] (1s<sup>2</sup> 2s<sup>2</sup> 2p<sup>4</sup>), [[fluorine]] (1s<sup>2</sup> 2s<sup>2</sup> 2p<sup>5</sup>), and [[neon]] (1s<sup>2</sup> 2s<sup>2</sup> 2p<sup>6</sup>) then complete the already singly filled 2p orbitals; the last of these fills the second shell completely.<ref name="FIII19" /><ref name=jensenlaw/>

Starting from element 11, [[sodium]], the second shell is full, making the second shell a core shell for this and all heavier elements. The eleventh electron begins the filling of the third shell by occupying a 3s orbital, giving a configuration of 1s<sup>2</sup> 2s<sup>2</sup> 2p<sup>6</sup> 3s<sup>1</sup> for sodium. This configuration is abbreviated [Ne] 3s<sup>1</sup>, where [Ne] represents neon's configuration. [[Magnesium]] ([Ne] 3s<sup>2</sup>) finishes this 3s orbital, and the following six elements [[aluminium]], [[silicon]], [[phosphorus]], [[sulfur]], [[chlorine]], and [[argon]] fill the three 3p orbitals ([Ne] 3s<sup>2</sup> 3p<sup>1</sup> through [Ne] 3s<sup>2</sup> 3p<sup>6</sup>).<ref name="FIII19"/><ref name=jensenlaw/> This creates an analogous series in which the outer shell structures of sodium through argon are analogous to those of lithium through neon, and is the basis for the periodicity of chemical properties that the periodic table illustrates:<ref name="FIII19" /> at regular but changing intervals of atomic numbers, the properties of the chemical elements approximately repeat.<ref name="Scerri17">Scerri, p. 17</ref>

The first 18 elements can thus be arranged as the start of a periodic table. Elements in the same column have the same number of valence electrons and have analogous valence electron configurations: these columns are called groups. The single exception is helium, which has two valence electrons like beryllium and magnesium, but is typically placed in the column of neon and argon to emphasise that its outer shell is full. (Some contemporary authors question even this single exception, preferring to consistently follow the valence configurations and place helium over beryllium.) There are eight columns in this periodic table fragment, corresponding to at most eight outer-shell electrons.<ref name="cartoon">{{cite book |last1=Gonick |first1=First |last2=Criddle |first2=Craig |date=2005 |title=The Cartoon Guide to Chemistry |publisher=Collins |pages=17–65 |isbn=0-06-093677-0}}</ref> A period begins when a new shell starts filling.<ref name="Petrucci331" /> Finally, the colouring illustrates the [[block (periodic table)|blocks]]: the elements in the s-block (coloured red) are filling s&nbsp;orbitals, while those in the p-block (coloured yellow) are filling p&nbsp;orbitals.<ref name="Petrucci331" />

{| class="wikitable" style="margin:auto;"
| bgcolor="{{element color|s-block}}" | 1<br />[[hydrogen|H]]
|
|
|
|
|
|
| bgcolor="{{element color|s-block}} | 2<br />[[helium|He]]
| 2×1 = '''2''' elements<br />{{inline block|bg={{element color|s-block}}|1s}} {{inline block|{{0|0p}}}}
|-
| bgcolor="{{element color|s-block}}" | 3<br />[[lithium|Li]]
| bgcolor="{{element color|s-block}}" | 4<br />[[beryllium|Be]]
| bgcolor="{{element color|p-block}}" | 5<br />[[boron|B]]
| bgcolor="{{element color|p-block}}" | 6<br />[[carbon|C]]
| bgcolor="{{element color|p-block}}" | 7<br />[[nitrogen|N]]
| bgcolor="{{element color|p-block}}" | 8<br />[[oxygen|O]]
| bgcolor="{{element color|p-block}}" | 9<br />[[fluorine|F]]
| bgcolor="{{element color|p-block}}" | 10<br />[[neon|Ne]]
| {{nowrap|2×(1+3) {{=}} '''8''' elements}}<br />{{inline block|bg={{element color|s-block}}|2s}} {{inline block|bg={{element color|p-block}}|2p}}
|-
| bgcolor="{{element color|s-block}}" | 11<br />[[sodium|Na]]
| bgcolor="{{element color|s-block}}" | 12<br />[[magnesium|Mg]]
| bgcolor="{{element color|p-block}}" | 13<br />[[aluminium|Al]]
| bgcolor="{{element color|p-block}}" | 14<br />[[silicon|Si]]
| bgcolor="{{element color|p-block}}" | 15<br />[[phosphorus|P]]
| bgcolor="{{element color|p-block}}" | 16<br />[[sulfur|S]]
| bgcolor="{{element color|p-block}}" | 17<br />[[chlorine|Cl]]
| bgcolor="{{element color|p-block}}" | 18<br />[[argon|Ar]]
| 2×(1+3) = '''8''' elements<br />{{inline block|bg={{element color|s-block}}|3s}} {{inline block|bg={{element color|p-block}}|3p}}
|}

Starting the next row, for [[potassium]] and [[calcium]] the 4s subshell is the lowest in energy, and therefore they fill it.<ref name="FIII19"/><ref name=jensenlaw/> Potassium adds one electron to the 4s shell ([Ar] 4s<sup>1</sup>), and calcium then completes it ([Ar] 4s<sup>2</sup>). However, starting from [[scandium]] ([Ar] 3d<sup>1</sup> 4s<sup>2</sup>) the 3d subshell becomes the next highest in energy. The 4s and 3d subshells have approximately the same energy and they compete for filling the electrons, and so the occupation is not quite consistently filling the 3d orbitals one at a time. The precise energy ordering of 3d and 4s changes along the row, and also changes depending on how many electrons are removed from the atom. For example, due to the repulsion between the 3d electrons and the 4s ones, at [[chromium]] the 4s energy level becomes slightly higher than 3d, and so it becomes more profitable for a chromium atom to have a [Ar] 3d<sup>5</sup> 4s<sup>1</sup> configuration than an [Ar] 3d<sup>4</sup> 4s<sup>2</sup> one. A similar anomaly occurs at [[copper]], whose atom has a [Ar] 3d<sup>10</sup> 4s<sup>1</sup> configuration rather than the expected [Ar] 3d<sup>9</sup> 4s<sup>2</sup>.<ref name="FIII19" /> These are violations of the Madelung rule. Such anomalies, however, do not have any chemical significance:<ref name="Jorgensen" /> most chemistry is not about isolated gaseous atoms,<ref>Wulfsberg, p. 27</ref> and the various configurations are so close in energy to each other<ref name="Petrucci328">Petrucci et al., p. 328</ref> that the presence of a nearby atom can shift the balance.<ref name="FIII19" /> Therefore, the periodic table ignores them and considers only idealized configurations.<ref name="Jensen2009">{{cite journal|author1-link=William B. Jensen |last1=Jensen |first1=William B. |date=2009 |title=Misapplying the Periodic Law |journal=Journal of Chemical Education |volume=86 |issue=10 |page=1186 |doi=10.1021/ed086p1186 |bibcode=2009JChEd..86.1186J |doi-access=free }}</ref>

At [[zinc]] ([Ar] 3d<sup>10</sup> 4s<sup>2</sup>), the 3d orbitals are completely filled with a total of ten electrons.<ref name="FIII19"/><ref name=jensenlaw/> Next come the 4p orbitals, completing the row, which are filled progressively by [[gallium]] ([Ar] 3d<sup>10</sup> 4s<sup>2</sup> 4p<sup>1</sup>) through [[krypton]] ([Ar] 3d<sup>10</sup> 4s<sup>2</sup> 4p<sup>6</sup>), in a manner analogous to the previous p-block elements.<ref name="FIII19" /><ref name=jensenlaw/> From gallium onwards, the 3d orbitals form part of the electronic core, and no longer participate in chemistry.<ref name=KW/> The s- and p-block elements, which fill their outer shells, are called [[main-group element]]s; the d-block elements (coloured blue below), which fill an inner shell, are called [[transition element]]s (or transition metals, since they are all metals).<ref name="Petrucci326">Petrucci et al., pp. 326–7</ref>

The next 18 elements fill the 5s orbitals ([[rubidium]] and [[strontium]]), then 4d ([[yttrium]] through [[cadmium]], again with a few anomalies along the way), and then 5p ([[indium]] through [[xenon]]).<ref name=Petrucci331/><ref name=jensenlaw/> Again, from indium onward the 4d orbitals are in the core.<ref name=jensenlaw/><ref>{{cite journal |last1=Farberovich |first1=O. V. |last2=Kurganskii |first2=S. I. |last3=Domashevskaya |first3=E. P. |date=1980 |title=Problems of the OPW Method. II. Calculation of the Band Structure of ZnS and CdS |url= |journal=Physica Status Solidi B |volume=97 |issue=2 |pages=631–640 |doi=10.1002/pssb.2220970230 |bibcode=1980PSSBR..97..631F }}</ref> Hence the fifth row has the same structure as the fourth.<ref name="Petrucci331" />

{| class="wikitable" style="margin:auto;"
| bgcolor="{{element color|s-block}}" | 1<br />[[hydrogen|H]]
|
|
|
|
|
|
|
|
|
|
|
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|
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|
|
| bgcolor="{{element color|s-block}} | 2<br />[[helium|He]]
| 2×1 = '''2''' elements<br />{{inline block|bg={{element color|s-block}}|1s}} {{inline block|{{0|0d}}}} {{inline block|{{0|0p}}}}
|-
| bgcolor="{{element color|s-block}}" | 3<br />[[lithium|Li]]
| bgcolor="{{element color|s-block}}" | 4<br />[[beryllium|Be]]
|
|
|
|
|
|
|
|
|
|
| bgcolor="{{element color|p-block}}" | 5<br />[[boron|B]]
| bgcolor="{{element color|p-block}}" | 6<br />[[carbon|C]]
| bgcolor="{{element color|p-block}}" | 7<br />[[nitrogen|N]]
| bgcolor="{{element color|p-block}}" | 8<br />[[oxygen|O]]
| bgcolor="{{element color|p-block}}" | 9<br />[[fluorine|F]]
| bgcolor="{{element color|p-block}}" | 10<br />[[neon|Ne]]
| 2×(1+3) = '''8''' elements<br />{{inline block|bg={{element color|s-block}}|2s}} {{inline block|{{0|0d}}}} {{inline block|bg={{element color|p-block}}|2p}}
|-
| bgcolor="{{element color|s-block}}" | 11<br />[[sodium|Na]]
| bgcolor="{{element color|s-block}}" | 12<br />[[magnesium|Mg]]
|
|
|
|
|
|
|
|
|
|
| bgcolor="{{element color|p-block}}" | 13<br />[[aluminium|Al]]
| bgcolor="{{element color|p-block}}" | 14<br />[[silicon|Si]]
| bgcolor="{{element color|p-block}}" | 15<br />[[phosphorus|P]]
| bgcolor="{{element color|p-block}}" | 16<br />[[sulfur|S]]
| bgcolor="{{element color|p-block}}" | 17<br />[[chlorine|Cl]]
| bgcolor="{{element color|p-block}}" | 18<br />[[argon|Ar]]
| 2×(1+3) = '''8''' elements<br />{{inline block|bg={{element color|s-block}}|3s}} {{inline block|{{0|0d}}}} {{inline block|bg={{element color|p-block}}|3p}}
|-
| bgcolor="{{element color|s-block}}" | 19<br />[[potassium|K]]
| bgcolor="{{element color|s-block}}" | 20<br />[[calcium|Ca]]
| bgcolor="{{element color|d-block}}" | 21<br />[[scandium|Sc]]
| bgcolor="{{element color|d-block}}" | 22<br />[[titanium|Ti]]
| bgcolor="{{element color|d-block}}" | 23<br />[[vanadium|V]]
| bgcolor="{{element color|d-block}}" | 24<br />[[chromium|Cr]]
| bgcolor="{{element color|d-block}}" | 25<br />[[manganese|Mn]]
| bgcolor="{{element color|d-block}}" | 26<br />[[iron|Fe]]
| bgcolor="{{element color|d-block}}" | 27<br />[[cobalt|Co]]
| bgcolor="{{element color|d-block}}" | 28<br />[[nickel|Ni]]
| bgcolor="{{element color|d-block}}" | 29<br />[[copper|Cu]]
| bgcolor="{{element color|d-block}}" | 30<br />[[zinc|Zn]]
| bgcolor="{{element color|p-block}}" | 31<br />[[gallium|Ga]]
| bgcolor="{{element color|p-block}}" | 32<br />[[germanium|Ge]]
| bgcolor="{{element color|p-block}}" | 33<br />[[arsenic|As]]
| bgcolor="{{element color|p-block}}" | 34<br />[[selenium|Se]]
| bgcolor="{{element color|p-block}}" | 35<br />[[bromine|Br]]
| bgcolor="{{element color|p-block}}" | 36<br />[[krypton|Kr]]
| {{nowrap|2×(1+3+5) {{=}} '''18''' elements}}<br />{{inline block|bg={{element color|s-block}}|4s}} {{inline block|bg={{element color|d-block}}|3d}} {{inline block|bg={{element color|p-block}}|4p}}
|-
| bgcolor="{{element color|s-block}}" | 37<br />[[rubidium|Rb]]
| bgcolor="{{element color|s-block}}" | 38<br />[[strontium|Sr]]
| bgcolor="{{element color|d-block}}" | 39<br />[[yttrium|Y]]
| bgcolor="{{element color|d-block}}" | 40<br />[[zirconium|Zr]]
| bgcolor="{{element color|d-block}}" | 41<br />[[niobium|Nb]]
| bgcolor="{{element color|d-block}}" | 42<br />[[molybdenum|Mo]]
| bgcolor="{{element color|d-block}}" | 43<br />[[technetium|Tc]]
| bgcolor="{{element color|d-block}}" | 44<br />[[ruthenium|Ru]]
| bgcolor="{{element color|d-block}}" | 45<br />[[rhodium|Rh]]
| bgcolor="{{element color|d-block}}" | 46<br />[[palladium|Pd]]
| bgcolor="{{element color|d-block}}" | 47<br />[[silver|Ag]]
| bgcolor="{{element color|d-block}}" | 48<br />[[cadmium|Cd]]
| bgcolor="{{element color|p-block}}" | 49<br />[[indium|In]]
| bgcolor="{{element color|p-block}}" | 50<br />[[tin|Sn]]
| bgcolor="{{element color|p-block}}" | 51<br />[[antimony|Sb]]
| bgcolor="{{element color|p-block}}" | 52<br />[[tellurium|Te]]
| bgcolor="{{element color|p-block}}" | 53<br />[[iodine|I]]
| bgcolor="{{element color|p-block}}" | 54<br />[[xenon|Xe]]
| 2×(1+3+5) = '''18''' elements<br />{{inline block|bg={{element color|s-block}}|5s}} {{inline block|bg={{element color|d-block}}|4d}} {{inline block|bg={{element color|p-block}}|5p}}
|}

The sixth row of the table likewise starts with two s-block elements: [[caesium]] and [[barium]].<ref name=jensenlaw/> After this, the first f-block elements (coloured green below) begin to appear, starting with [[lanthanum]]. These are sometimes termed inner transition elements.<ref name="Petrucci326" /> As there are now not only 4f but also 5d and 6s subshells at similar energies, competition occurs once again with many irregular configurations;<ref name="Petrucci328" /> this resulted in some dispute about where exactly the f-block is supposed to begin, but most who study the matter agree that it starts at lanthanum in accordance with the Aufbau principle.<ref name="Jensen-2015" /> Even though lanthanum does not itself fill the 4f subshell as a single atom, because of repulsion between electrons,<ref name="Jorgensen">{{cite journal |last1=Jørgensen |first1=Christian |date=1973 |title=The Loose Connection between Electron Configuration and the Chemical Behavior of the Heavy Elements (Transuranics) |journal=Angewandte Chemie International Edition |volume=12 |issue=1 |pages=12–19 |doi=10.1002/anie.197300121}}</ref> its 4f orbitals are low enough in energy to participate in chemistry.<ref name="Hamilton">{{cite journal |last1=Hamilton |first1=David C. |date=1965 |title=Position of Lanthanum in the Periodic Table |journal=American Journal of Physics |volume=33 |issue=8 |pages=637–640 |doi=10.1119/1.1972042|bibcode=1965AmJPh..33..637H}}</ref><ref name=elyashevich>{{cite book |last=El'yashevich |first=M. A. |author-link= |date=1953 |title=Spectra of the Rare Earths |url= |location=Moscow |publisher=State Publishing House of Technical-Theoretical Literature |pages=382, 397 |isbn=}}</ref><ref name=Cp3Ln>{{cite journal | last1=Krinsky | first1=Jamin L. | last2=Minasian | first2=Stefan G. | last3=Arnold | first3=John | title=Covalent Lanthanide Chemistry Near the Limit of Weak Bonding: Observation of (CpSiMe<sub>3</sub>)<sub>3</sub>Ce−ECp* and a Comprehensive Density Functional Theory Analysis of Cp<sub>3</sub>Ln−ECp (E = Al, Ga) | journal=Inorganic Chemistry | publisher=American Chemical Society (ACS) | volume=50 | issue=1 | date=8 December 2010 | issn=0020-1669 | doi=10.1021/ic102028d | pages=345–357| pmid=21141834 }}</ref> At [[ytterbium]], the seven 4f orbitals are completely filled with fourteen electrons; thereafter, a series of ten transition elements ([[lutetium]] through [[mercury (element)|mercury]]) follows,<ref name=jensenlaw/><ref name="JensenLr">{{cite web|url=https://www.che.uc.edu/jensen/W.%20B.%20Jensen/Reprints/251.%20Lawrencium.pdf |title=Some Comments on the Position of Lawrencium in the Periodic Table |last1=Jensen |first1=W. B. |date=2015 |access-date=20 September 2015 |archive-url=https://web.archive.org/web/20151223091325/https://www.che.uc.edu/jensen/W.%20B.%20Jensen/Reprints/251.%20Lawrencium.pdf |archive-date=23 December 2015 }}</ref><ref>{{cite journal |last1=Wang |first1=Fan |last2=Le-Min |first2=Li |date=2002 |title=镧系元素 4f 轨道在成键中的作用的理论研究 |trans-title=Theoretical Study on the Role of Lanthanide 4f Orbitals in Bonding |language=zh |journal=Acta Chimica Sinica |volume=62 |issue=8 |pages=1379–84}}</ref><ref name="LaF3">{{cite journal |last1=Xu |first1=Wei |last2=Ji |first2=Wen-Xin |first3=Yi-Xiang |last3=Qiu |first4=W. H. Eugen |last4=Schwarz |first5=Shu-Guang |last5=Wang |date=2013 |title=On structure and bonding of lanthanoid trifluorides LnF<sub>3</sub> (Ln = La to Lu) |journal=Physical Chemistry Chemical Physics |volume=2013 |issue=15 |pages=7839–47 |doi=10.1039/C3CP50717C|pmid=23598823 |bibcode=2013PCCP...15.7839X }}</ref> and finally six main-group elements ([[thallium]] through [[radon]]) complete the period.<ref name=jensenlaw/><ref name="Pyykko">{{cite journal
| title = Octacarbonyl Ion Complexes of Actinides [An(CO)8]+/− (An=Th, U) and the Role of f Orbitals in Metal–Ligand Bonding
| first1= Chaoxian |last1=Chi |first2=Sudip |last2=Pan | first3= Jiaye |last3=Jin |first4=Luyan |last4=Meng | first5= Mingbiao |last5=Luo |first6=Lili |last6=Zhao |first7=Mingfei |last7=Zhou |first8=Gernot |last8=Frenking
| journal = [[Chemistry: A European Journal|Chem. Eur. J.]]
| year = 2019
| volume = 25
| issue = 50
| pages = 11772–11784
| doi = 10.1002/chem.201902625
| pmid= 31276242 | pmc= 6772027 |doi-access=free }}</ref> From lutetium onwards the 4f orbitals are in the core,<ref name=jensenlaw/><ref name=Cp3Ln/> and from thallium onwards so are the 5d orbitals.<ref name=jensenlaw/><ref name=KW/><ref>{{cite journal |last1=Singh |first1=Prabhakar P. |date=1994 |title=Relativistic effects in mercury: Atom, clusters, and bulk |url= |journal=Physical Review B |volume=49 |issue=7 |pages=4954–4958 |doi=10.1103/PhysRevB.49.4954 |pmid=10011429 |bibcode=1994PhRvB..49.4954S }}</ref>

The seventh row is analogous to the sixth row: 7s fills ([[francium]] and [[radium]]), then 5f ([[actinium]] to [[nobelium]]), then 6d ([[lawrencium]] to [[copernicium]]), and finally 7p ([[nihonium]] to [[oganesson]]).<ref name=jensenlaw/> Starting from lawrencium the 5f orbitals are in the core,<ref name=jensenlaw/> and probably the 6d orbitals join the core starting from nihonium.<ref name=jensenlaw/><ref name=VI>{{cite journal |last1=Hu |first1=Shu-Xian |last2=Zou |first2=Wenli |date=23 September 2021 |title=Stable copernicium hexafluoride (CnF<sub>6</sub>) with an oxidation state of VI+ |journal=Physical Chemistry Chemical Physics |volume=2022 |issue=24 |pages=321–325 |doi=10.1039/D1CP04360A|pmid=34889909 |bibcode=2021PCCP...24..321H }}</ref>{{efn|Compounds that would use the 6d orbitals of nihonium as valence orbitals have been theoretically investigated, but they are all expected to be too unstable to observe.<ref name="Seth">{{cite journal |last1=Seth |first1=Michael |last2=Schwerdtfeger |first2=Peter |first3=Knut |last3=Fægri |date=1999 |title=The chemistry of superheavy elements. III. Theoretical studies on element 113 compounds |journal=Journal of Chemical Physics |volume=111 |issue=14 |pages=6422–6433 |doi=10.1063/1.480168 |bibcode=1999JChPh.111.6422S|s2cid=41854842 |doi-access=free |hdl=2292/5178 |hdl-access=free }}</ref>}} Again there are a few anomalies along the way:<ref name="Petrucci331">Petrucci et al., p. 331</ref> for example, as single atoms neither actinium nor [[thorium]] actually fills the 5f subshell, and lawrencium does not fill the 6d shell, but all these subshells can still become filled in chemical environments.<ref>{{cite journal |last1=Kelley |first1=Morgan P. |last2=Deblonde |first2=Gauthier J.-P. |first3=Jing |last3=Su |first4=Corwin H. |last4=Booth |first5=Rebecca J. |last5=Abergel |first6=Enrique R. |last6=Batista |first7=Ping |last7=Yang |date=2018 |title=Bond Covalency and Oxidation State of Actinide Ions Complexed with Therapeutic Chelating Agent 3,4,3-LI(1,2-HOPO) |url= https://escholarship.org/uc/item/4tc1b0xz|journal=Inorganic Chemistry |volume=57 |issue=9 |pages=5352–5363 |doi=10.1021/acs.inorgchem.8b00345 |pmid=29624372 |osti=1458511 }}</ref><ref name="Johansson">{{cite journal|last1=Johansson |first1=B. |last2=Abuja |first2=R. |last3=Eriksson |first3=O. |last4=Wills |first4=J. M. |display-authors=3 |year=1995 |title=Anomalous fcc crystal structure of thorium metal. |journal=Physical Review Letters |volume=75 |issue=2 |pages=280–283 |doi=10.1103/PhysRevLett.75.280|pmid=10059654 |bibcode=1995PhRvL..75..280J|url=https://zenodo.org/record/1233903 }}</ref><ref name=XuPyykko>
{{cite journal |last1=Xu |first1=Wen-Hua |last2=Pyykkö |first2=Pekka |date=8 June 2016 |url=http://pubs.rsc.org/-/content/articlehtml/2016/cp/c6cp02706g |title=Is the chemistry of lawrencium peculiar |journal=Phys. Chem. Chem. Phys. |volume=2016 |issue=18 |pages=17351–5 |doi=10.1039/c6cp02706g |pmid=27314425 |access-date=24 April 2017|bibcode=2016PCCP...1817351X |hdl=10138/224395 |s2cid=31224634 |hdl-access=free }}</ref> For a very long time, the seventh row was incomplete as most of its elements do not occur in nature. The missing [[transuranic element|elements beyond uranium]] started to be synthesized in the laboratory in 1940, when neptunium was made.<ref name="Scerri354" /> (However, the first element to be discovered by synthesis rather than in nature was technetium in 1937.) The row was completed with the synthesis of [[tennessine]] in 2010<ref name="117s">{{cite journal |last1=Oganessian |first1=Yu.Ts. |author-link1=Yuri Oganessian |last2=Abdullin |first2=F.Sh. |last3=Bailey |first3=P.D. |last4=Benker |first4=D.E. |last5=Bennett |first5=M.E. |last6=Dmitriev |first6=S.N. |last7=Ezold |first7=J.G. |last8=Hamilton |first8=J.H. |last9=Henderson |first9=R.A. |first10=M.G. |last10=Itkis |first11=Yuri V. |last11=Lobanov |first12=A.N. |last12=Mezentsev |first13=K. J. |last13=Moody |first14=S.L. |last14=Nelson |first15=A.N. |last15=Polyakov |first16=C.E. |last16=Porter |first17=A.V. |last17=Ramayya |first18=F.D. |last18=Riley |first19=J.B. |last19=Roberto |first20=M. A. |last20=Ryabinin |first21=K.P. |last21=Rykaczewski |first22=R.N. |last22=Sagaidak |first23=D.A. |last23=Shaughnessy |first24=I.V. |last24=Shirokovsky |first25=M.A. |last25=Stoyer |first26=V.G. |last26=Subbotin |first27=R. |last27=Sudowe |first28=A.M. |last28=Sukhov |first29=Yu.S. |last29=Tsyganov |first30=Vladimir K. |last30=Utyonkov |first31=A.A. |last31=Voinov |first32=G.K. |last32=Vostokin |first33=P.A. |last33=Wilk |display-authors=6 |title=Synthesis of a new element with atomic number {{nowrap|''Z'' {{=}} 117}} |year=2010 |journal=Physical Review Letters |volume=104 |issue=14 |page=142502 |doi=10.1103/PhysRevLett.104.142502 |pmid=20481935 |bibcode=2010PhRvL.104n2502O |s2cid=3263480 |doi-access=free }}</ref> (the last element [[oganesson]] had already been made in 2002),<ref name="pp2002">{{cite journal|author=Oganessian, Yu. T.|display-authors=etal|title=Results from the first <sup>249</sup>Cf+<sup>48</sup>Ca experiment|url=https://www.jinr.ru/publish/Preprints/2002/287(D7-2002-287)e.pdf|journal=JINR Communication|date=2002|access-date=13 June 2009|archive-date=13 December 2004|archive-url=https://web.archive.org/web/20041213100709/https://www.jinr.ru/publish/Preprints/2002/287%28D7-2002-287%29e.pdf}}</ref> and the last elements in this seventh row were given names in 2016.<ref name="IUPAC-20161130">{{cite news |author=<!--Not stated--> |title=IUPAC Announces the Names of the Elements 113, 115, 117, and 118 |url=https://iupac.org/iupac-announces-the-names-of-the-elements-113-115-117-and-118/ |date=30 November 2016 |work=[[IUPAC]] |access-date=1 December 2016 |archive-date=30 November 2016 |archive-url=https://web.archive.org/web/20161130111959/https://iupac.org/iupac-announces-the-names-of-the-elements-113-115-117-and-118/ |url-status=live }}</ref>
<div style="overflow-x:auto">
{| class="wikitable" style="margin:auto;"
| bgcolor="{{element color|s-block}}" | 1<br />[[hydrogen|H]]
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| bgcolor="{{element color|s-block}} | 2<br />[[helium|He]]
| 2×1 = '''2''' elements<br />{{inline block|bg={{element color|s-block}}|1s}} {{inline block|{{0|0f}}}} {{inline block|{{0|0d}}}} {{inline block|{{0|0p}}}}
|-
| bgcolor="{{element color|s-block}}" | 3<br />[[lithium|Li]]
| bgcolor="{{element color|s-block}}" | 4<br />[[beryllium|Be]]
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| bgcolor="{{element color|p-block}}" | 5<br />[[boron|B]]
| bgcolor="{{element color|p-block}}" | 6<br />[[carbon|C]]
| bgcolor="{{element color|p-block}}" | 7<br />[[nitrogen|N]]
| bgcolor="{{element color|p-block}}" | 8<br />[[oxygen|O]]
| bgcolor="{{element color|p-block}}" | 9<br />[[fluorine|F]]
| bgcolor="{{element color|p-block}}" | 10<br />[[neon|Ne]]
| 2×(1+3) = '''8''' elements<br />{{inline block|bg={{element color|s-block}}|2s}} {{inline block|{{0|0f}}}} {{inline block|{{0|0d}}}} {{inline block|bg={{element color|p-block}}|2p}}
|-
| bgcolor="{{element color|s-block}}" | 11<br />[[sodium|Na]]
| bgcolor="{{element color|s-block}}" | 12<br />[[magnesium|Mg]]
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| bgcolor="{{element color|p-block}}" | 13<br />[[aluminium|Al]]
| bgcolor="{{element color|p-block}}" | 14<br />[[silicon|Si]]
| bgcolor="{{element color|p-block}}" | 15<br />[[phosphorus|P]]
| bgcolor="{{element color|p-block}}" | 16<br />[[sulfur|S]]
| bgcolor="{{element color|p-block}}" | 17<br />[[chlorine|Cl]]
| bgcolor="{{element color|p-block}}" | 18<br />[[argon|Ar]]
| 2×(1+3) = '''8''' elements<br />{{inline block|bg={{element color|s-block}}|3s}} {{inline block|{{0|0f}}}} {{inline block|{{0|0d}}}} {{inline block|bg={{element color|p-block}}|3p}}
|-
| bgcolor="{{element color|s-block}}" | 19<br />[[potassium|K]]
| bgcolor="{{element color|s-block}}" | 20<br />[[calcium|Ca]]
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| bgcolor="{{element color|d-block}}" | 21<br />[[scandium|Sc]]
| bgcolor="{{element color|d-block}}" | 22<br />[[titanium|Ti]]
| bgcolor="{{element color|d-block}}" | 23<br />[[vanadium|V]]
| bgcolor="{{element color|d-block}}" | 24<br />[[chromium|Cr]]
| bgcolor="{{element color|d-block}}" | 25<br />[[manganese|Mn]]
| bgcolor="{{element color|d-block}}" | 26<br />[[iron|Fe]]
| bgcolor="{{element color|d-block}}" | 27<br />[[cobalt|Co]]
| bgcolor="{{element color|d-block}}" | 28<br />[[nickel|Ni]]
| bgcolor="{{element color|d-block}}" | 29<br />[[copper|Cu]]
| bgcolor="{{element color|d-block}}" | 30<br />[[zinc|Zn]]
| bgcolor="{{element color|p-block}}" | 31<br />[[gallium|Ga]]
| bgcolor="{{element color|p-block}}" | 32<br />[[germanium|Ge]]
| bgcolor="{{element color|p-block}}" | 33<br />[[arsenic|As]]
| bgcolor="{{element color|p-block}}" | 34<br />[[selenium|Se]]
| bgcolor="{{element color|p-block}}" | 35<br />[[bromine|Br]]
| bgcolor="{{element color|p-block}}" | 36<br />[[krypton|Kr]]
| 2×(1+3+5) = '''18''' elements<br />{{inline block|bg={{element color|s-block}}|4s}} {{inline block|{{0|0f}}}} {{inline block|bg={{element color|d-block}}|3d}} {{inline block|bg={{element color|p-block}}|4p}}
|-
| bgcolor="{{element color|s-block}}" | 37<br />[[rubidium|Rb]]
| bgcolor="{{element color|s-block}}" | 38<br />[[strontium|Sr]]
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| bgcolor="{{element color|d-block}}" | 39<br />[[yttrium|Y]]
| bgcolor="{{element color|d-block}}" | 40<br />[[zirconium|Zr]]
| bgcolor="{{element color|d-block}}" | 41<br />[[niobium|Nb]]
| bgcolor="{{element color|d-block}}" | 42<br />[[molybdenum|Mo]]
| bgcolor="{{element color|d-block}}" | 43<br />[[technetium|Tc]]
| bgcolor="{{element color|d-block}}" | 44<br />[[ruthenium|Ru]]
| bgcolor="{{element color|d-block}}" | 45<br />[[rhodium|Rh]]
| bgcolor="{{element color|d-block}}" | 46<br />[[palladium|Pd]]
| bgcolor="{{element color|d-block}}" | 47<br />[[silver|Ag]]
| bgcolor="{{element color|d-block}}" | 48<br />[[cadmium|Cd]]
| bgcolor="{{element color|p-block}}" | 49<br />[[indium|In]]
| bgcolor="{{element color|p-block}}" | 50<br />[[tin|Sn]]
| bgcolor="{{element color|p-block}}" | 51<br />[[antimony|Sb]]
| bgcolor="{{element color|p-block}}" | 52<br />[[tellurium|Te]]
| bgcolor="{{element color|p-block}}" | 53<br />[[iodine|I]]
| bgcolor="{{element color|p-block}}" | 54<br />[[xenon|Xe]]
| 2×(1+3+5) = '''18''' elements<br />{{inline block|bg={{element color|s-block}}|5s}} {{inline block|{{0|0f}}}} {{inline block|bg={{element color|d-block}}|4d}} {{inline block|bg={{element color|p-block}}|5p}}
|-
| bgcolor="{{element color|s-block}}" | 55<br />[[caesium|Cs]]
| bgcolor="{{element color|s-block}}" | 56<br />[[barium|Ba]]
| bgcolor="{{element color|f-block}}" | 57<br />[[lanthanum|La]]
| bgcolor="{{element color|f-block}}" | 58<br />[[cerium|Ce]]
| bgcolor="{{element color|f-block}}" | 59<br />[[praseodymium|Pr]]
| bgcolor="{{element color|f-block}}" | 60<br />[[neodymium|Nd]]
| bgcolor="{{element color|f-block}}" | 61<br />[[promethium|Pm]]
| bgcolor="{{element color|f-block}}" | 62<br />[[samarium|Sm]]
| bgcolor="{{element color|f-block}}" | 63<br />[[europium|Eu]]
| bgcolor="{{element color|f-block}}" | 64<br />[[gadolinium|Gd]]
| bgcolor="{{element color|f-block}}" | 65<br />[[terbium|Tb]]
| bgcolor="{{element color|f-block}}" | 66<br />[[dysprosium|Dy]]
| bgcolor="{{element color|f-block}}" | 67<br />[[holmium|Ho]]
| bgcolor="{{element color|f-block}}" | 68<br />[[erbium|Er]]
| bgcolor="{{element color|f-block}}" | 69<br />[[thulium|Tm]]
| bgcolor="{{element color|f-block}}" | 70<br />[[ytterbium|Yb]]
| bgcolor="{{element color|d-block}}" | 71<br />[[lutetium|Lu]]
| bgcolor="{{element color|d-block}}" | 72<br />[[hafnium|Hf]]
| bgcolor="{{element color|d-block}}" | 73<br />[[tantalum|Ta]]
| bgcolor="{{element color|d-block}}" | 74<br />[[tungsten|W]]
| bgcolor="{{element color|d-block}}" | 75<br />[[rhenium|Re]]
| bgcolor="{{element color|d-block}}" | 76<br />[[osmium|Os]]
| bgcolor="{{element color|d-block}}" | 77<br />[[iridium|Ir]]
| bgcolor="{{element color|d-block}}" | 78<br />[[platinum|Pt]]
| bgcolor="{{element color|d-block}}" | 79<br />[[gold|Au]]
| bgcolor="{{element color|d-block}}" | 80<br />[[mercury (element)|Hg]]
| bgcolor="{{element color|p-block}}" | 81<br />[[thallium|Tl]]
| bgcolor="{{element color|p-block}}" | 82<br />[[lead|Pb]]
| bgcolor="{{element color|p-block}}" | 83<br />[[bismuth|Bi]]
| bgcolor="{{element color|p-block}}" | 84<br />[[polonium|Po]]
| bgcolor="{{element color|p-block}}" | 85<br />[[astatine|At]]
| bgcolor="{{element color|p-block}}" | 86<br />[[radon|Rn]]
| {{nowrap|2×(1+3+5+7) {{=}} '''32''' elements}}<br />{{nowrap|{{inline block|bg={{element color|s-block}}|6s}} {{inline block|bg={{element color|f-block}}|4f}} {{inline block|bg={{element color|d-block}}|5d}} {{inline block|bg={{element color|p-block}}|6p}}}}
|-
| bgcolor="{{element color|s-block}}" | 87<br />[[francium|Fr]]
| bgcolor="{{element color|s-block}}" | 88<br />[[radium|Ra]]
| bgcolor="{{element color|f-block}}" | 89<br />[[actinium|Ac]]
| bgcolor="{{element color|f-block}}" | 90<br />[[thorium|Th]]
| bgcolor="{{element color|f-block}}" | 91<br />[[protactinium|Pa]]
| bgcolor="{{element color|f-block}}" | 92<br />[[uranium|U]]
| bgcolor="{{element color|f-block}}" | 93<br />[[neptunium|Np]]
| bgcolor="{{element color|f-block}}" | 94<br />[[plutonium|Pu]]
| bgcolor="{{element color|f-block}}" | 95<br />[[americium|Am]]
| bgcolor="{{element color|f-block}}" | 96<br />[[curium|Cm]]
| bgcolor="{{element color|f-block}}" | 97<br />[[berkelium|Bk]]
| bgcolor="{{element color|f-block}}" | 98<br />[[californium|Cf]]
| bgcolor="{{element color|f-block}}" | 99<br />[[einsteinium|Es]]
| bgcolor="{{element color|f-block}}" | 100<br />[[fermium|Fm]]
| bgcolor="{{element color|f-block}}" | 101<br />[[mendelevium|Md]]
| bgcolor="{{element color|f-block}}" | 102<br />[[nobelium|No]]
| bgcolor="{{element color|d-block}}" | 103<br />[[lawrencium|Lr]]
| bgcolor="{{element color|d-block}}" | 104<br />[[rutherfordium|Rf]]
| bgcolor="{{element color|d-block}}" | 105<br />[[dubnium|Db]]
| bgcolor="{{element color|d-block}}" | 106<br />[[seaborgium|Sg]]
| bgcolor="{{element color|d-block}}" | 107<br />[[bohrium|Bh]]
| bgcolor="{{element color|d-block}}" | 108<br />[[hassium|Hs]]
| bgcolor="{{element color|d-block}}" | 109<br />[[meitnerium|Mt]]
| bgcolor="{{element color|d-block}}" | 110<br />[[darmstadtium|Ds]]
| bgcolor="{{element color|d-block}}" | 111<br />[[roentgenium|Rg]]
| bgcolor="{{element color|d-block}}" | 112<br />[[copernicium|Cn]]
| bgcolor="{{element color|p-block}}" | 113<br />[[nihonium|Nh]]
| bgcolor="{{element color|p-block}}" | 114<br />[[flerovium|Fl]]
| bgcolor="{{element color|p-block}}" | 115<br />[[moscovium|Mc]]
| bgcolor="{{element color|p-block}}" | 116<br />[[livermorium|Lv]]
| bgcolor="{{element color|p-block}}" | 117<br />[[tennessine|Ts]]
| bgcolor="{{element color|p-block}}" | 118<br />[[oganesson|Og]]
| 2×(1+3+5+7) = '''32''' elements<br />{{inline block|bg={{element color|s-block}}|7s}} {{inline block|bg={{element color|f-block}}|5f}} {{inline block|bg={{element color|d-block}}|6d}} {{inline block|bg={{element color|p-block}}|7p}}
|}
</div>
This completes the modern periodic table, with all seven rows completely filled to capacity.<ref name="IUPAC-20161130" /><!--when 8th row elements are discovered, replace them here and write "The eighth row finishes prematurely as we run out of elements discovered."-->

===Electron configuration table===
The following table shows the electron configuration of a neutral gas-phase atom of each element. Different configurations can be favoured in different chemical environments.<ref name="Jorgensen" /> The main-group elements have entirely regular electron configurations; the transition and inner transition elements show twenty irregularities due to the aforementioned competition between subshells close in energy level. For the last ten elements (109–118), experimental data is lacking<ref>{{cite journal |url=https://www.nist.gov/pml/periodic-table-elements |title=Periodic Table of the Elements |author=[[National Institute of Standards and Technology]] (NIST) |date=August 2019 |journal=NIST |access-date=7 February 2021 |archive-date=8 February 2021 |archive-url=https://web.archive.org/web/20210208182536/https://www.nist.gov/pml/periodic-table-elements |url-status=live }}</ref> and therefore calculated configurations have been shown instead.<ref>{{cite journal |last1=Fricke |first1=B. |editor-last=Dunitz |editor-first=J. D. |year=1975 |journal=Structure and Bonding |volume=21 |pages=89–144 |title=Superheavy elements a prediction of their chemical and physical properties|publisher=Springer-Verlag |location=Berlin |doi=10.1007/BFb0116496|isbn=978-3-540-07109-9 }}</ref> Completely filled subshells have been greyed out.

{{Periodic table (electron configuration)}}