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
, beginning with
and ending with ununoctium
, the heaviest element currently discovered. As a rule, period 7 elements fill their 7s
first, then their 5f, 6d, and 7p shells, in that order, however there are exceptions, such as protactinium
All elements of period 7 are
. This period contains the
, which contains the heaviest naturally occurring element,
; 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,
elements have only been identified in laboratories in batches of a few atoms at a time: of these, ununtrium
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
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
and relativistic effects, ultimately caused by the very high positive electrical charge from their massive atomic nuclei
Francium and radium make up the s-block elements of the 7th period.
) is a
with atomic number
88, represented by the symbol Ra
. Radium is an almost pure-white
alkaline earth metal
, but it readily
on exposure to air, becoming black in color. All isotopes of radium are highlyradioactive
, with the most stable
, which has a
of 1601 years and decays
gas. Because of such instability, radium is luminescent
, glowing a faint blue. Radium, in the form of
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.
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
element, is also generally considered an actinide. In comparison with the lanthanides
, also mostly
elements, the actinides show much more variable valence
Of the actinides,
occur naturally in substantial, primordial
, quantities and small amounts of persisting natural
have also been identified. The radioactive decay of uranium produces transient amounts of actinium
, and atoms of
are occasionally produced from transmutation
reactions in uranium ores
. The other actinides are purely
Nuclear weapons tests have released at least six actinides heavier than plutonium into the environment
; analysis of debris from a 1952
explosion showed the presence of americium
All actinides are
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
of most modern smoke detectors
In presentations of the
, the lanthanides and the actinides are customarily shown as two additional rows below the main body of the table,
with placeholders or else a selected single element of each series (either lanthanum
, and either
, respectively) shown in a single cell of the main table, between
, respectively. This convention is entirely a matter of
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).
Transactinide elements are also
, that is, have an atomic number greater than that of
(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
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.
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.)
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.
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.
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.
Actually the least unstable isotope, francium-223
Some synthetic elements, like
technetium, have later been found in nature.
Luis A. Orozco (2003).
Chemical and Engineering News.
The Manhattan Project. An Interactive History. US Department of Energy
Gray, Theodore (2009).
The Elements: A Visual Exploration of Every Known Atom in the Universe. New York: Black Dog & Leventhal Publishers. p. 240.
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.
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".
(1): 180. Bibcode:1956PhRv..102..180F.
IUPAC Provisional Recommendations for the Nomenclature of Inorganic Chemistry (2004)
(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.