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 plutonium.
All elements of period 7 are radioactive. This period contains the actinides, which contains the heaviest naturally occurring element, plutonium; subsequent elements must be synthesized artificially. Whilst the first five of these 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.
|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|
(*) Exception to the Madelung rule.
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.
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.
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. 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.
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, 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).
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). 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:
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.
In atomic physics and quantum chemistry, the electron configuration is the distribution of electrons of an atom or molecule (or other physical structure) in atomic or molecular orbitals. For example, the electron configuration of the neon atom is 1s2 2s2 2p6, using the notation explained below.
Electronic configurations describe each electron as moving independently in an orbital, in an average field created by all other orbitals. Mathematically, configurations are described by Slater determinants or configuration state functions.
According to the laws of quantum mechanics, for systems with only one electron, a level of energy is associated with each electron configuration and in certain conditions, electrons are able to move from one configuration to another by the emission or absorption of a quantum of energy, in the form of a photon.
Knowledge of the electron configuration of different atoms is useful in understanding the structure of the periodic table of elements. This is also useful for describing the chemical bonds that hold atoms together. In bulk materials, this same idea helps explain the peculiar properties of lasers and semiconductors.Extended periodic table
An extended periodic table theorizes about chemical elements beyond those currently known in the periodic table and proven up through oganesson, which completes the seventh period (row) in the periodic table at atomic number (Z) 118.
If further elements with higher atomic numbers than this are discovered, they will be placed in additional periods, laid out (as with the existing periods) to illustrate periodically recurring trends in the properties of the elements concerned. Any additional periods are expected to contain a larger number of elements than the seventh period, as they are calculated to have an additional so-called g-block, containing at least 18 elements with partially filled g-orbitals in each period. An eight-period table containing this block was suggested by Glenn T. Seaborg in 1969. The first element of the g-block may have atomic number 121, and thus would have the systematic name unbiunium. Despite many searches, no elements in this region have been synthesized or discovered in nature.According to the orbital approximation in quantum mechanical descriptions of atomic structure, the g-block would correspond to elements with partially filled g-orbitals, but spin-orbit coupling effects reduce the validity of the orbital approximation substantially for elements of high atomic number. While Seaborg's version of the extended period had the heavier elements following the pattern set by lighter elements, as it did not take into account relativistic effects, models that take relativistic effects into account do not. Pekka Pyykkö and Burkhard Fricke used computer modeling to calculate the positions of elements up to Z = 172, and found that several were displaced from the Madelung rule. As a result of uncertainty and variability in predictions of chemical and physical properties of elements beyond 120, there is currently no consensus on their placement in the extended periodic table.
Elements in this region are likely to be highly unstable with respect to radioactive decay and undergo alpha decay or spontaneous fission with extremely short half-lives, though element 126 is hypothesized to be within an island of stability that is resistant to fission but not to alpha decay. Other islands of stability beyond the known elements may also be possible, including one theorized around element 164, though the extent of stabilizing effects from closed nuclear shells is uncertain. It is not clear how many elements beyond the expected island of stability are physically possible, whether period 8 is complete, or if there is a period 9. The International Union of Pure and Applied Chemistry (IUPAC) defines an element to exist if its lifetime is longer than 10−14 seconds (0.01 picoseconds, or 10 femtoseconds), which is the time it takes for the nucleus to form an electron cloud.As early as 1940, it was noted that a simplistic interpretation of the relativistic Dirac equation runs into problems with electron orbitals at Z > 1/α ≈ 137, suggesting that neutral atoms cannot exist beyond element 137, and that a periodic table of elements based on electron orbitals therefore breaks down at this point. On the other hand, a more rigorous analysis calculates the analogous limit to be Z ≈ 173 where the 1s subshell dives into the Dirac sea, and that it is instead not neutral atoms that cannot exist beyond element 173, but bare nuclei, thus posing no obstacle to the further extension of the periodic system. Atoms beyond this critical atomic number are called supercritical atoms.Index of chemistry articles
Chemistry (from Egyptian kēme (chem), meaning "earth") is the physical science concerned with the composition, structure, and properties of matter, as well as the changes it undergoes during chemical reactions.Below is a list of chemistry-related articles. Chemical compounds are listed separately at list of organic compounds, list of inorganic compounds or list of biomolecules.
|Periodic table forms|
|Sets of elements|