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Aperiod 7 element is one of thechemical elements in the seventh row (orperiod) of theperiodic table of the chemical elements. The periodic table is laid out in rows to illustrate recurring (periodic) trends in the chemical behavior of the elements as their atomic number increases: a new row is begun when chemical behavior begins to repeat, meaning that elements with similar behavior fall into the same vertical columns. The seventh period contains 32 elements, tied for the most withperiod 6, beginning withfrancium and ending withoganesson, the heaviest element currently discovered. As a rule, period 7 elements fill their 7sshells first, then their 5f, 6d, and 7p shells in that order, but there are exceptions, such asuranium.
All period 7 elements areradioactive. This period contains theactinides, which includeplutonium, the last naturally occurring element;[1][note 1] subsequent elements must be created artificially. While the first five of thesesynthetic elements (americium througheinsteinium) are now available inmacroscopic quantities, most are extremely rare, having only been prepared inmicrogram amounts or less. The latertransactinide elements have only been identified in laboratories in batches of a few atoms at a time.
Though the rarity of many of these elements means that experimental results are not many, their periodic and group trends are less well defined than other periods. Whilstfrancium andradium do show typical properties of their respective groups,actinides display a much greater variety of behavior and oxidation states than thelanthanides. These peculiarities are due to a variety of factors, including a large degree ofspin–orbit coupling and relativistic effects, ultimately caused by the very high electric charge of their massivenuclei. Periodicity mostly holds throughout the 6d series and is predicted also formoscovium andlivermorium, but the other four 7p elements,nihonium,flerovium,tennessine, andoganesson, are predicted to have very different properties from those expected for their groups.
| Chemical element | Block | Electron configuration | Occurrence | ||
|---|---|---|---|---|---|
| 87 | Fr | Francium | s-block | [Rn] 7s1 | From decay |
| 88 | Ra | Radium | s-block | [Rn] 7s2 | From decay |
| 89 | Ac | Actinium | f-block | [Rn] 6d1 7s2 (*) | From decay |
| 90 | Th | Thorium | f-block | [Rn] 6d2 7s2 (*) | Primordial |
| 91 | Pa | Protactinium | f-block | [Rn] 5f2 6d1 7s2 (*) | From decay |
| 92 | U | Uranium | f-block | [Rn] 5f3 6d1 7s2 (*) | Primordial |
| 93 | Np | Neptunium | f-block | [Rn] 5f4 6d1 7s2 (*) | From decay |
| 94 | Pu | Plutonium | f-block | [Rn] 5f6 7s2 | From decay |
| 95 | Am | Americium | f-block | [Rn] 5f7 7s2 | Synthetic |
| 96 | Cm | Curium | f-block | [Rn] 5f7 6d1 7s2 (*) | Synthetic |
| 97 | Bk | Berkelium | f-block | [Rn] 5f9 7s2 | Synthetic |
| 98 | Cf | Californium | f-block | [Rn] 5f10 7s2 | Synthetic |
| 99 | Es | Einsteinium | f-block | [Rn] 5f11 7s2 | Synthetic |
| 100 | Fm | Fermium | f-block | [Rn] 5f12 7s2 | Synthetic |
| 101 | Md | Mendelevium | f-block | [Rn] 5f13 7s2 | Synthetic |
| 102 | No | Nobelium | f-block | [Rn] 5f14 7s2 | Synthetic |
| 103 | Lr | Lawrencium | d-block | [Rn] 5f14 7s2 7p1 (*) | Synthetic |
| 104 | Rf | Rutherfordium | d-block | [Rn] 5f14 6d2 7s2 | Synthetic |
| 105 | Db | Dubnium | d-block | [Rn] 5f14 6d3 7s2 | Synthetic |
| 106 | Sg | Seaborgium | d-block | [Rn] 5f14 6d4 7s2 | Synthetic |
| 107 | Bh | Bohrium | d-block | [Rn] 5f14 6d5 7s2 | Synthetic |
| 108 | Hs | Hassium | d-block | [Rn] 5f14 6d6 7s2 | Synthetic |
| 109 | Mt | Meitnerium | d-block | [Rn] 5f14 6d7 7s2 (?) | Synthetic |
| 110 | Ds | Darmstadtium | d-block | [Rn] 5f14 6d8 7s2 (?) | Synthetic |
| 111 | Rg | Roentgenium | d-block | [Rn] 5f14 6d9 7s2 (?) | Synthetic |
| 112 | Cn | Copernicium | d-block | [Rn] 5f14 6d10 7s2 (?) | Synthetic |
| 113 | Nh | Nihonium | p-block | [Rn] 5f14 6d10 7s2 7p1 (?) | Synthetic |
| 114 | Fl | Flerovium | p-block | [Rn] 5f14 6d10 7s2 7p2 (?) | Synthetic |
| 115 | Mc | Moscovium | p-block | [Rn] 5f14 6d10 7s2 7p3 (?) | Synthetic |
| 116 | Lv | Livermorium | p-block | [Rn] 5f14 6d10 7s2 7p4 (?) | Synthetic |
| 117 | Ts | Tennessine | p-block | [Rn] 5f14 6d10 7s2 7p5 (?) | Synthetic |
| 118 | Og | Oganesson | p-block | [Rn] 5f14 6d10 7s2 7p6 (?) | Synthetic |
(?) Prediction
(*) Exception to theMadelung rule.
In many periodic tables, the f-block is erroneously shifted one element to the right, so that lanthanum and actinium become d-block elements, and Ce–Lu and Th–Lr form the f-block tearing the d-block into two very uneven portions. This is a holdover from early erroneous measurements of electron configurations.[4]Lev Landau andEvgeny Lifshitz pointed out in 1948 that lutetium is not an f-block element,[5] and since then physical, chemical, and electronic evidence has overwhelmingly supported that the f-block contains the elements La–Yb and Ac–No,[4][6] as shown here and as supported byInternational Union of Pure and Applied Chemistry reports dating from 1988[6] and 2021.[7]
Francium and radium make up the s-block elements of the 7th period.
Francium(Fr, atomic number 87) is a highlyradioactive metal that decays into astatine,radium, orradon. It is one of the two leastelectronegative elements; the other iscaesium. As analkali metal, it has onevalence electron. Francium was discovered byMarguerite Perey inFrance (from which the element takes its name) in 1939.[8] It was the last element discovered innature, rather than by synthesis.[note 2] Outside the laboratory, francium is extremely rare, with trace amounts found inuranium andthorium ores, where theisotope francium-223 continually forms and decays. As little as 20–30 g (one ounce) exists at any given time throughoutEarth's crust; the other isotopes are entirely synthetic. The largest amount produced in the laboratory was a cluster of more than 300,000 atoms.[9]
Radium (Ra, atomic number 88) is an almost pure-whitealkaline earth metal, but it readilyoxidizes, reacting with nitrogen (rather than oxygen) on exposure to air, becoming black in color. Allisotopes of radium areradioactive; the most stable isradium-226, which has ahalf-life of 1601 years anddecays intoradon. Due to such instability, radiumluminesces, glowing a faint blue. Radium, in the form ofradium chloride, wasdiscovered byMarie andPierre Curie in 1898. They extracted the radium compound fromuraninite and published the discovery at theFrench Academy of Sciences five days later. Radium was isolated in itsmetallic state by Marie Curie andAndré-Louis Debierne throughelectrolysis of radium chloride in 1910. Since its discovery, it has given names such asradium A andradium C2 to several isotopes of other elements that aredecay products of radium-226. In nature, radium is found inuranium ores in trace amounts as small as a seventh of a gram per ton ofuraninite. Radium is not necessary for living things, and adverse health effects are likely when it is incorporated into biochemical processes due to its radioactivity and chemical reactivity.
Theactinide oractinoid (IUPAC nomenclature) series encompasses the 15metallicchemical elements withatomic numbers from 89 to 103,actinium throughlawrencium.[11][12][13][14]
The actinide series is named after its first element actinium. All but one of the actinides aref-block elements, corresponding to the filling of the 5felectron shell; lawrencium, ad-block element, is also generally considered an actinide. In comparison with thelanthanides, also mostlyf-block elements, the actinides show much more variablevalence.
Of the actinides,thorium anduranium occur naturally in substantial,primordial, quantities. Radioactive decay of uranium produces transient amounts ofactinium,protactinium andplutonium, and atoms ofneptunium andplutonium are occasionally produced fromtransmutation inuranium ores. The other actinides are purelysynthetic elements, though the first six actinides after plutonium would have been produced atOklo (and long since decayed away), andcurium almost certainly previously existed in nature as anextinct radionuclide.[11][15] Nuclear tests have released at least six actinides heavier than plutonium into theenvironment; analysis of debris from a 1952hydrogen bomb explosion showed the presence ofamericium,curium,berkelium,californium,einsteinium andfermium.[16]
All actinides areradioactive and release energy upon radioactive decay; naturally occurring uranium and thorium, and synthetically produced plutonium are the most abundant actinides on Earth. These are used innuclear reactors andnuclear weapons. Uranium and thorium also have diverse current or historical uses, and americium is used in theionization chambers of most modernsmoke detectors.
In presentations of theperiodic table, the lanthanides and the actinides are customarily shown as two additional rows below the main body of the table,[11] with placeholders or else a selected single element of each series (eitherlanthanum orlutetium, and eitheractinium orlawrencium, respectively) shown in a single cell of the main table, betweenbarium andhafnium, andradium andrutherfordium, respectively. This convention is entirely a matter ofaesthetics and formatting practicality; a rarely usedwide-formatted periodic table (32 columns) shows the lanthanide and actinide series in their proper columns, as parts of the table's sixth and seventh rows (periods).
Transactinide elements (also,transactinides, orsuper-heavy elements, orsuperheavies) are thechemical elements withatomic numbers greater than those of theactinides, the heaviest of which islawrencium (103).[17][18] All transactinides of period 7 have been discovered, up tooganesson (element 118).
Superheavies are alsotransuranic elements, that is, have atomic number greater than that ofuranium (92). The further distinction of having an atomic number greater than the actinides is significant in several ways:
Transactinides areradioactive and have only been obtained synthetically in laboratories. None of these elements has ever been collected in a macroscopic sample. Transactinides are all named after scientists, or important locations involved in the synthesis of the elements.
Chemistry Nobel Prize winnerGlenn T. Seaborg, who first proposed theactinide concept which led to the acceptance of theactinide series, also proposed the existence of a transactinide series ranging from element 104 to 121 and asuperactinide series approximately spanning elements 122 to 153. The transactinideseaborgium is named in his honor.
IUPAC defines an element to exist if its lifetime is longer than 10−14 second, the time needed to form an electron cloud.[19]
