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 ununoctium, 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 protactinium.

Properties

All elements of period 7 are radioactive. This period contains the actinides, which contains the heaviest naturally occurring element, californium; subsequent elements must be synthesized artificially. Whilst one of these (einsteinium) is 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: of these, ununtrium, ununpentium and those beyond livermorium have not been recognised by the IUPAC.

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.

Elements

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

(?) Prediction

(*) Exception to the Madelung rule.

(**) Probably an exception to the Madelung rule.

Francium and radium

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

Francium (/ˈfrænsiəm/ FRAN-see-əm) 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 (/ˈreɪdiəm/ RAY-dee-əm) 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 highlyradioactive, 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 likeradium 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; lawrencium, 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 and small amounts of persisting natural plutonium have also been identified. The radioactive decay of uranium produces transient amounts of actinium and protactinium, and atoms of neptunium, americium, curium, berkelium and californium are occasionally produced from transmutation reactions in uranium ores. The other actinides are purely synthetic elements.^[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, including 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). The last actinide, lawrencium, also has one electron in the 6d subshell.
• Except for dubnium, even the longest-lasting isotopes of 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 names are replaced with two-letter names 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 Nobelist 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.

The term transactinide is an adjective, and is not commonly used alone as a noun to refer to the transactinide elements.

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

Notes

References