Period 7 element

A period 7 element is one of the chemical elements in the seventh row (or period) of the periodic table of the chemical elements. The periodic table is laid out in rows to illustrate recurring (periodic) trends in the chemical behaviour of the elements as their atomic number increases: a new row is begun when chemical behaviour begins to repeat, meaning that elements with similar behaviour fall into the same vertical columns. The seventh period contains 32 elements, tied for the most with period 6, beginning with francium and ending with oganesson, the heaviest element currently discovered. As a rule, period 7 elements fill their 7s shells first, then their 5f, 6d, and 7p shells, in that order; however, there are exceptions, such as uranium.

Properties

All elements of period 7 are radioactive. This period contains the actinides, which includes plutonium, the naturally occurring element with the heaviest nucleus; subsequent elements must be created artificially. While the first five of these synthetic elements (americium through einsteinium) are now available in macroscopic quantities, most are extremely rare, having only been prepared in microgram amounts or less. The later transactinide elements have only been identified in laboratories in batches of a few atoms at a time.

Although the rarity of many of these elements means that experimental results are not very extensive, their periodic and group trends are less well defined than other periods. Whilst francium and radium do show typical properties of their respective groups, actinides display a much greater variety of behaviour and oxidation states than the lanthanides. These peculiarities are due to a variety of factors, including a large degree of spin-orbit coupling and relativistic effects, ultimately caused by the very high positive electrical charge from their massive atomic nuclei. Periodicity mostly holds throughout the 6d series, and at moscovium and livermorium; but the other four 7p elements, nihonium, flerovium, tennessine, and oganesson, have very different properties from those expected for their groups.

Elements

Chemical element			Chemical series	Electron configuration	Occurrence

87	Fr	Francium	Alkali metal	[Rn] 7s¹	From decay
88	Ra	Radium	Alkaline earth metal	[Rn] 7s²	From decay
89	Ac	Actinium	Actinide	[Rn] 6d¹ 7s² (*)	From decay
90	Th	Thorium	Actinide	[Rn] 6d² 7s² (*)	Primordial
91	Pa	Protactinium	Actinide	[Rn] 5f² 6d¹ 7s² (*)	From decay
92	U	Uranium	Actinide	[Rn] 5f³ 6d¹ 7s² (*)	Primordial
93	Np	Neptunium	Actinide	[Rn] 5f⁴ 6d¹ 7s² (*)	From decay
94	Pu	Plutonium	Actinide	[Rn] 5f⁶ 7s²	From decay
95	Am	Americium	Actinide	[Rn] 5f⁷ 7s²	Synthetic
96	Cm	Curium	Actinide	[Rn] 5f⁷ 6d¹ 7s² (*)	Synthetic
97	Bk	Berkelium	Actinide	[Rn] 5f⁹ 7s²	Synthetic
98	Cf	Californium	Actinide	[Rn] 5f¹⁰ 7s²	Synthetic
99	Es	Einsteinium	Actinide	[Rn] 5f¹¹ 7s²	Synthetic
100	Fm	Fermium	Actinide	[Rn] 5f¹² 7s²	Synthetic
101	Md	Mendelevium	Actinide	[Rn] 5f¹³ 7s²	Synthetic
102	No	Nobelium	Actinide	[Rn] 5f¹⁴ 7s²	Synthetic
103	Lr	Lawrencium	Actinide	[Rn] 5f¹⁴ 7s² 7p¹ (*)	Synthetic
104	Rf	Rutherfordium	Transition metal	[Rn] 5f¹⁴ 6d² 7s²	Synthetic
105	Db	Dubnium	Transition metal	[Rn] 5f¹⁴ 6d³ 7s²	Synthetic
106	Sg	Seaborgium	Transition metal	[Rn] 5f¹⁴ 6d⁴ 7s²	Synthetic
107	Bh	Bohrium	Transition metal	[Rn] 5f¹⁴ 6d⁵ 7s²	Synthetic
108	Hs	Hassium	Transition metal	[Rn] 5f¹⁴ 6d⁶ 7s²	Synthetic
109	Mt	Meitnerium	Transition metal (?)	[Rn] 5f¹⁴ 6d⁷ 7s² (?)	Synthetic
110	Ds	Darmstadtium	Transition metal (?)	[Rn] 5f¹⁴ 6d⁸ 7s² (?)	Synthetic
111	Rg	Roentgenium	Transition metal (?)	[Rn] 5f¹⁴ 6d⁹ 7s² (?)	Synthetic
112	Cn	Copernicium	Post-transition metal	[Rn] 5f¹⁴ 6d¹⁰ 7s² (?)	Synthetic
113	Nh	Nihonium	Post-transition metal (?)	[Rn] 5f¹⁴ 6d¹⁰ 7s² 7p¹ (?)	Synthetic
114	Fl	Flerovium	Post-transition metal (?)	[Rn] 5f¹⁴ 6d¹⁰ 7s² 7p² (?)	Synthetic
115	Mc	Moscovium	Post-transition metal (?)	[Rn] 5f¹⁴ 6d¹⁰ 7s² 7p³ (?)	Synthetic
116	Lv	Livermorium	Post-transition metal (?)	[Rn] 5f¹⁴ 6d¹⁰ 7s² 7p⁴ (?)	Synthetic
117	Ts	Tennessine	Post-transition metal (?)	[Rn] 5f¹⁴ 6d¹⁰ 7s² 7p⁵ (?)	Synthetic
118	Og	Oganesson	Noble gas (?)	[Rn] 5f¹⁴ 6d¹⁰ 7s² 7p⁶ (?)	Synthetic

(?) Prediction

(*) Exception to the Madelung rule.

Francium and radium

Francium and radium make up the s-block elements of the 7th period.

Francium is a chemical element with symbol Fr and atomic number 87. It was formerly known as eka-caesium and actinium K.^{[note 1]} It is one of the two least electronegative elements, the other being caesium. Francium is a highly radioactive metal that decays into astatine, radium, and radon. As an alkali metal, it has one valence electron. Francium was discovered by Marguerite Perey in France (from which the element takes its name) in 1939. It was the last element discovered in nature, rather than by synthesis.^{[note 2]} Outside the laboratory, francium is extremely rare, with trace amounts found in uranium and thorium ores, where the isotope francium-223 continually forms and decays. As little as 20–30 g (one ounce) exists at any given time throughout the Earth's crust; the other isotopes are entirely synthetic. The largest amount produced in the laboratory was a cluster of more than 300,000 atoms.^[1]

Radium is a chemical element with atomic number 88, represented by the symbol Ra. Radium is an almost pure-white alkaline earth metal, but it readily oxidizes on exposure to air, becoming black in color. All isotopes of radium are highly radioactive, with the most stable isotope being radium-226, which has a half-life of 1601 years and decays into radon gas. Because of such instability, radium is luminescent, glowing a faint blue. Radium, in the form of radium chloride, was discovered by Marie Skłodowska-Curie and Pierre Curie in 1898. They extracted the radium compound from uraninite and published the discovery at the French Academy of Sciences five days later. Radium was isolated in its metallic state by Marie Curie and André-Louis Debierne through the electrolysis of radium chloride in 1910. Since its discovery, it has given names such as radium A and radium C₂ to several isotopes of other elements that are decay products of radium-226. In nature, radium is found in uranium ores in trace amounts as small as a seventh of a gram per ton of uraninite. Radium is not necessary for living organisms, and adverse health effects are likely when it is incorporated into biochemical processes because of its radioactivity and chemical reactivity.

Actinides

The atomic bomb dropped on Nagasaki had a plutonium charge.^[2]

The actinide or actinoid (IUPAC nomenclature) series encompasses the 15 metallic chemical elements with atomic numbers from 89 to 103, actinium through lawrencium.^[3]^[4]^[5]^[6]

The actinide series derives its name from the group 3 element actinium. All but one of the actinides are f-block elements, corresponding to the filling of the 5f electron shell; actinium, a d-block element, is also generally considered an actinide. In comparison with the lanthanides, also mostly f-block elements, the actinides show much more variable valence.

Of the actinides, thorium and uranium occur naturally in substantial, primordial, quantities. The radioactive decay of uranium produces transient amounts of actinium, protactinium and plutonium, and atoms of neptunium are occasionally produced from transmutation reactions in uranium ores. The other actinides are purely synthetic elements, although the first six actinides after plutonium would have been produced during the Oklo phenomenon (and long since decayed away), and curium almost certainly previously existed in nature as an extinct radionuclide.^[3]^[7] Nuclear weapons tests have released at least six actinides heavier than plutonium into the environment; analysis of debris from a 1952 hydrogen bomb explosion showed the presence of americium, curium, berkelium, californium, einsteinium and fermium.^[8]

All actinides are radioactive 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 in nuclear reactors and nuclear weapons. Uranium and thorium also have diverse current or historical uses, and americium is used in the ionization chambers of most modern smoke detectors.

In presentations of the periodic table, the lanthanides and the actinides are customarily shown as two additional rows below the main body of the table,^[3] with placeholders or else a selected single element of each series (either lanthanum or lutetium, and either actinium or lawrencium, respectively) shown in a single cell of the main table, between barium and hafnium, and radium and rutherfordium, respectively. This convention is entirely a matter of aesthetics and formatting practicality; a rarely used wide-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).

Transactinides

Transactinide elements (also, transactinides, or super-heavy elements) are the chemical elements with atomic numbers greater than those of the actinides, the heaviest of which is lawrencium (103).^[9]^[10] All transactinides of period 7 have been discovered, up to oganesson (element 118).

Transactinide elements are also transuranic elements, that is, have an atomic number greater than that of uranium (92), an actinide. The further distinction of having an atomic number greater than the actinides is significant in several ways:

The transactinide elements all have electrons in the 6d subshell in their ground state (and thus are placed in the d-block).
Even the longest-lasting isotopes of many transactinide elements have extremely short half-lives, measured in seconds or smaller units.
The element naming controversy involved the first five or six transactinide elements. These elements thus used three-letter systematic names for many years after their discovery had been confirmed. (Usually the three-letter symbols are replaced with two-letter symbols relatively shortly after a discovery has been confirmed.)

Transactinides are radioactive and have only been obtained synthetically in laboratories. None of these elements has ever been collected in a macroscopic sample. Transactinide elements are all named after nuclear physicists and chemists or important locations involved in the synthesis of the elements.

Chemistry Nobel Prize winner Glenn T. Seaborg, who first proposed the actinide concept which led to the acceptance of the actinide series, also proposed the existence of a transactinide series ranging from element 104 to 121 and a superactinide series approximately spanning elements 122 to 153. The transactinide seaborgium is named in his honor.

IUPAC defines an element to exist if its lifetime is longer than 10⁻¹⁴ seconds, the time needed for the nucleus to form an electronic cloud.^[11]

Notes

^ Actually the least unstable isotope, francium-223
^ Some synthetic elements, like technetium, have later been found in nature.

References

^ Luis A. Orozco (2003). "Francium". Chemical and Engineering News.
^ The Manhattan Project. An Interactive History. US Department of Energy
^ ^a ^b ^c Gray, Theodore (2009). The Elements: A Visual Exploration of Every Known Atom in the Universe. New York: Black Dog & Leventhal Publishers. p. 240. ISBN 978-1-57912-814-2.
^ Actinide element, Encyclopædia Britannica on-line
^ Although "actinoid" (rather than "actinide") means "actinium-like" and therefore should exclude actinium, that element it is usually included in the series.
^ Connelly, Neil G.; et al. (2005). "Elements". Nomenclature of Inorganic Chemistry. London: Royal Society of Chemistry. p. 52. ISBN 978-0-85404-438-2.
^ Greenwood, p. 1250
^ Fields, P.; Studier, M.; Diamond, H.; Mech, J.; Inghram, M.; Pyle, G.; Stevens, C.; Fried, S.; Manning, W. (1956). "Transplutonium Elements in Thermonuclear Test Debris". Physical Review. 102 (1): 180. Bibcode:1956PhRv..102..180F. doi:10.1103/PhysRev.102.180.
^ IUPAC Provisional Recommendations for the Nomenclature of Inorganic Chemistry (2004) Archived 2006-10-27 at the Wayback Machine (online draft of an updated version of the "Red Book" IR 3–6)
^ Morss, Lester R.; Edelstein, Norman M.; Fuger, Jean, eds. (2006). The Chemistry of the Actinide and Transactinide Elements (3rd ed.). Dordrecht, The Netherlands: Springer. ISBN 978-1-4020-3555-5.
^ "Kernchemie".

[1] Actually the least unstable isotope, francium-223

[2] Some synthetic elements, like technetium, have later been found in nature.

[chemnews-3] Luis A. Orozco (2003). "Francium". Chemical and Engineering News.

[4] The Manhattan Project. An Interactive History. US Department of Energy

[Gray-5] Gray, Theodore (2009). The Elements: A Visual Exploration of Every Known Atom in the Universe. New York: Black Dog & Leventhal Publishers. p. 240. ISBN 978-1-57912-814-2.

[6] Actinide element, Encyclopædia Britannica on-line

[7] Although "actinoid" (rather than "actinide") means "actinium-like" and therefore should exclude actinium, that element it is usually included in the series.

[8] Connelly, Neil G.; et al. (2005). "Elements". Nomenclature of Inorganic Chemistry. London: Royal Society of Chemistry. p. 52. ISBN 978-0-85404-438-2.

[g1250-9] Greenwood, p. 1250

[10] Fields, P.; Studier, M.; Diamond, H.; Mech, J.; Inghram, M.; Pyle, G.; Stevens, C.; Fried, S.; Manning, W. (1956). "Transplutonium Elements in Thermonuclear Test Debris". Physical Review. 102 (1): 180. Bibcode:1956PhRv..102..180F. doi:10.1103/PhysRev.102.180.

[11] IUPAC Provisional Recommendations for the Nomenclature of Inorganic Chemistry (2004) Archived 2006-10-27 at the Wayback Machine (online draft of an updated version of the "Red Book" IR 3–6)

[12] Morss, Lester R.; Edelstein, Norman M.; Fuger, Jean, eds. (2006). The Chemistry of the Actinide and Transactinide Elements (3rd ed.). Dordrecht, The Netherlands: Springer. ISBN 978-1-4020-3555-5.

[13] "Kernchemie".

[note 1]

[note 2]

[1]

[2]

[3]

[4]

[5]

[6]

[7]

[8]

[9]

[10]

[11]