Francium | |||||||||||||||||||||||||||||||||||
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Pronunciation | /ˈfrænsiəm/ | ||||||||||||||||||||||||||||||||||
Mass number | [223] | ||||||||||||||||||||||||||||||||||
Francium in the periodic table | |||||||||||||||||||||||||||||||||||
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Atomic number (Z) | 87 | ||||||||||||||||||||||||||||||||||
Group | group 1: hydrogen and alkali metals | ||||||||||||||||||||||||||||||||||
Period | period 7 | ||||||||||||||||||||||||||||||||||
Block | s-block | ||||||||||||||||||||||||||||||||||
Electron configuration | [ Rn ] 7s1 | ||||||||||||||||||||||||||||||||||
Electrons per shell | 2, 8, 18, 32, 18, 8, 1 | ||||||||||||||||||||||||||||||||||
Physical properties | |||||||||||||||||||||||||||||||||||
Phase at STP | solid | ||||||||||||||||||||||||||||||||||
Melting point | 300 K (27 °C,81 °F) | ||||||||||||||||||||||||||||||||||
Boiling point | 950 K(677 °C,1251 °F) | ||||||||||||||||||||||||||||||||||
Density (near r.t.) | 2.458 g/cm3(estimated) [1] | ||||||||||||||||||||||||||||||||||
Vapor pressure (extrapolated)
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Atomic properties | |||||||||||||||||||||||||||||||||||
Oxidation states | +1 (expected to have a strongly basic oxide) | ||||||||||||||||||||||||||||||||||
Electronegativity | Pauling scale: >0.79 | ||||||||||||||||||||||||||||||||||
Ionization energies |
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Covalent radius | 260 pm (extrapolated) | ||||||||||||||||||||||||||||||||||
Van der Waals radius | 348 pm(extrapolated) | ||||||||||||||||||||||||||||||||||
Other properties | |||||||||||||||||||||||||||||||||||
Natural occurrence | from decay | ||||||||||||||||||||||||||||||||||
Crystal structure | body-centered cubic (bcc) (extrapolated) [1] | ||||||||||||||||||||||||||||||||||
Lattice constant | a = 670.4 pm (estimated) [1] | ||||||||||||||||||||||||||||||||||
Thermal conductivity | 15 W/(m⋅K)(extrapolated) | ||||||||||||||||||||||||||||||||||
Electrical resistivity | 3 µΩ⋅m(calculated) | ||||||||||||||||||||||||||||||||||
Magnetic ordering | Paramagnetic | ||||||||||||||||||||||||||||||||||
CAS Number | 7440-73-5 | ||||||||||||||||||||||||||||||||||
History | |||||||||||||||||||||||||||||||||||
Naming | after France, homeland of the discoverer | ||||||||||||||||||||||||||||||||||
Discovery and first isolation | Marguerite Perey (1939) | ||||||||||||||||||||||||||||||||||
Isotopes of francium | |||||||||||||||||||||||||||||||||||
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Francium is a chemical element; it has symbol Fr and atomic number 87. It is extremely radioactive; its most stable isotope, francium-223 (originally called actinium K after the natural decay chain in which it appears), has a half-life of only 22 minutes. [4] It is the second-most electropositive element, behind only caesium, and is the second rarest naturally occurring element (after astatine). Francium's isotopes decay quickly into astatine, radium, and radon. The electronic structure of a francium atom is [Rn] 7s1; thus, the element is classed as an alkali metal.
Bulk francium has never been seen. Because of the general appearance of the other elements in its periodic table column, it is presumed that francium would appear as a highly reactive metal if enough could be collected together to be viewed as a bulk solid or liquid. Obtaining such a sample is highly improbable since the extreme heat of decay resulting from its short half-life would immediately vaporize any viewable quantity of the element.
Francium was discovered by Marguerite Perey [5] in France (from which the element takes its name) on January 7, 1939. [6] Before its discovery, francium was referred to as eka-caesium or ekacaesium because of its conjectured existence below caesium in the periodic table. It was the last element first discovered in nature, rather than by synthesis. [note 1] Outside the laboratory, francium is extremely rare, with trace amounts found in uranium ores, where the isotope francium-223 (in the family of uranium-235) continually forms and decays. As little as 1 ounce (28 g) exists at any given time throughout the Earth's crust; aside from francium-223 and francium-221, its other isotopes are entirely synthetic. The largest amount produced in the laboratory was a cluster of more than 300,000 atoms. [7]
Francium is one of the most unstable of the naturally occurring elements: its longest-lived isotope, francium-223, has a half-life of only 22 minutes. The only comparable element is astatine, whose most stable natural isotope, astatine-219 (the alpha daughter of francium-223), has a half-life of 56 seconds, although synthetic astatine-210 is much longer-lived with a half-life of 8.1 hours. [8] All isotopes of francium decay into astatine, radium, or radon. [8] Francium-223 also has a shorter half-life than the longest-lived isotope of each synthetic element up to and including element 105, dubnium. [9]
Francium is an alkali metal whose chemical properties mostly resemble those of caesium. [9] A heavy element with a single valence electron, [10] it has the highest equivalent weight of any element. [9] Liquid francium—if created—should have a surface tension of 0.05092 N/m at its melting point. [11] Francium's melting point was estimated to be around 8.0 °C (46.4 °F); [12] a value of 27 °C (81 °F) is also often encountered. [9] The melting point is uncertain because of the element's extreme rarity and radioactivity; a different extrapolation based on Dmitri Mendeleev's method gave 20 ± 1.5 °C (68.0 ± 2.7 °F). A calculation based on the melting temperatures of binary ionic crystals gives 24.861 ± 0.517 °C (76.750 ± 0.931 °F). [13] The estimated boiling point of 620 °C (1,148 °F) is also uncertain; the estimates 598 °C (1,108 °F) and 677 °C (1,251 °F), as well as the extrapolation from Mendeleev's method of 640 °C (1,184 °F), have also been suggested. [12] [11] The density of francium is expected to be around 2.48 g/cm3 (Mendeleev's method extrapolates 2.4 g/cm3). [12]
Linus Pauling estimated the electronegativity of francium at 0.7 on the Pauling scale, the same as caesium; [14] the value for caesium has since been refined to 0.79, but there are no experimental data to allow a refinement of the value for francium. [15] Francium has a slightly higher ionization energy than caesium, [16] 392.811(4) kJ/mol as opposed to 375.7041(2) kJ/mol for caesium, as would be expected from relativistic effects, and this would imply that caesium is the less electronegative of the two. Francium should also have a higher electron affinity than caesium and the Fr− ion should be more polarizable than the Cs− ion. [17]
As a result of francium's instability, its salts are only known to a small extent. Francium coprecipitates with several caesium salts, such as caesium perchlorate, which results in small amounts of francium perchlorate. This coprecipitation can be used to isolate francium, by adapting the radiocaesium coprecipitation method of Lawrence E. Glendenin and C. M. Nelson. It will additionally coprecipitate with many other caesium salts, including the iodate, the picrate, the tartrate (also rubidium tartrate), the chloroplatinate, and the silicotungstate. It also coprecipitates with silicotungstic acid, and with perchloric acid, without another alkali metal as a carrier, which leads to other methods of separation. [18] [19]
Francium perchlorate is produced by the reaction of francium chloride and sodium perchlorate. The francium perchlorate coprecipitates with caesium perchlorate. [19] This coprecipitation can be used to isolate francium, by adapting the radiocaesium coprecipitation method of Lawrence E. Glendenin and C. M. Nelson. However, this method is unreliable in separating thallium, which also coprecipitates with caesium. [19] Francium perchlorate's entropy is expected to be 42.7 e.u [12] (178.7 J mol−1 K−1).
Francium halides are all soluble in water and are expected to be white solids. They are expected to be produced by the reaction of the corresponding halogens. For example, francium chloride would be produced by the reaction of francium and chlorine. Francium chloride has been studied as a pathway to separate francium from other elements, by using the high vapour pressure of the compound, although francium fluoride would have a higher vapour pressure. [12]
Francium nitrate, sulfate, hydroxide, carbonate, acetate, and oxalate, are all soluble in water, while the iodate, picrate, tartrate, chloroplatinate, and silicotungstate are insoluble. The insolubility of these compounds are used to extract francium from other radioactive products, such as zirconium, niobium, molybdenum, tin, antimony, the method mentioned in the section above. [12] Francium oxide is believed to disproportionate to the peroxide and francium metal. [20] The CsFr molecule is predicted to have francium at the negative end of the dipole, unlike all known heterodiatomic alkali metal molecules. Francium superoxide (FrO2) is expected to have a more covalent character than its lighter congeners; this is attributed to the 6p electrons in francium being more involved in the francium–oxygen bonding. [17] The relativistic destabilisation of the 6p3/2 spinor may make francium compounds in oxidation states higher than +1 possible, such as [FrVF6]−; but this has not been experimentally confirmed. [21]
There are 37 known isotopes of francium ranging in atomic mass from 197 to 233. [3] Francium has seven metastable nuclear isomers. [9] Francium-223 and francium-221 are the only isotopes that occur in nature, with the former being far more common. [22]
Francium-223 is the most stable isotope, with a half-life of 21.8 minutes, [9] and it is highly unlikely that an isotope of francium with a longer half-life will ever be discovered or synthesized. [23] Francium-223 is a fifth product of the uranium-235 decay series as a daughter isotope of actinium-227; thorium-227 is the more common daughter. [24] Francium-223 then decays into radium-223 by beta decay (1.149 MeV decay energy), with a minor (0.006%) alpha decay path to astatine-219 (5.4 MeV decay energy). [25]
Francium-221 has a half-life of 4.8 minutes. [9] It is the ninth product of the neptunium decay series as a daughter isotope of actinium-225. [24] Francium-221 then decays into astatine-217 by alpha decay (6.457 MeV decay energy). [9] Although all primordial 237Np is extinct, the neptunium decay series continues to exist naturally in tiny traces due to (n,2n) knockout reactions in natural 238U. [26] Francium-222, with a half-life of 14 minutes, may be produced as a result of the beta decay of natural radon-222; this process, though energetically possible, has nonetheless not yet been observed. [27]
The least stable ground state isotope is francium-215, with a half-life of 90 ns: [3] it undergoes a 9.54 MeV alpha decay to astatine-211. [9]
Due to its instability and rarity, there are no commercial applications for francium. [28] [29] [30] [24] It has been used for research purposes in the fields of chemistry [31] and of atomic structure. Its use as a potential diagnostic aid for various cancers has also been explored, [8] but this application has been deemed impractical. [29]
Francium's ability to be synthesized, trapped, and cooled, along with its relatively simple atomic structure, has made it the subject of specialized spectroscopy experiments. These experiments have led to more specific information regarding energy levels and the coupling constants between subatomic particles. [32] Studies on the light emitted by laser-trapped francium-210 ions have provided accurate data on transitions between atomic energy levels which are fairly similar to those predicted by quantum theory. [33]
As early as 1870, chemists thought that there should be an alkali metal beyond caesium, with an atomic number of 87. [8] It was then referred to by the provisional name eka-caesium . [34]
In 1914, Stefan Meyer, Viktor F. Hess, and Friedrich Paneth (working in Vienna) made measurements of alpha radiation from various substances, including 227Ac. They observed the possibility of a minor alpha branch of this nuclide, though follow-up work could not be done due to the outbreak of World War I. Their observations were not precise and sure enough for them to announce the discovery of element 87, though it is likely that they did indeed observe the decay of 227Ac to 223Fr. [34]
Soviet chemist Dmitry Dobroserdov was the first scientist to claim to have found eka-caesium, or francium. In 1925, he observed weak radioactivity in a sample of potassium, another alkali metal, and incorrectly concluded that eka-caesium was contaminating the sample (the radioactivity from the sample was from the naturally occurring potassium radioisotope, potassium-40). [35] He then published a thesis on his predictions of the properties of eka-caesium, in which he named the element russium after his home country. [36] Shortly thereafter, Dobroserdov began to focus on his teaching career at the Polytechnic Institute of Odesa, and he did not pursue the element further. [35]
The following year, English chemists Gerald J. F. Druce and Frederick H. Loring analyzed X-ray photographs of manganese(II) sulfate. [36] They observed spectral lines which they presumed to be of eka-caesium. They announced their discovery of element 87 and proposed the name alkalinium, as it would be the heaviest alkali metal. [35]
In 1930, Fred Allison of the Alabama Polytechnic Institute claimed to have discovered element 87 (in addition to 85) when analyzing pollucite and lepidolite using his magneto-optical machine. Allison requested that it be named virginium after his home state of Virginia, along with the symbols Vi and Vm. [36] [37] In 1934, H.G. MacPherson of UC Berkeley disproved the effectiveness of Allison's device and the validity of his discovery. [38]
In 1936, Romanian physicist Horia Hulubei and his French colleague Yvette Cauchois also analyzed pollucite, this time using their high-resolution X-ray apparatus. [35] They observed several weak emission lines, which they presumed to be those of element 87. Hulubei and Cauchois reported their discovery and proposed the name moldavium, along with the symbol Ml, after Moldavia, the Romanian province where Hulubei was born. [36] In 1937, Hulubei's work was criticized by American physicist F. H. Hirsh Jr., who rejected Hulubei's research methods. Hirsh was certain that eka-caesium would not be found in nature, and that Hulubei had instead observed mercury or bismuth X-ray lines. Hulubei insisted that his X-ray apparatus and methods were too accurate to make such a mistake. Because of this, Jean Baptiste Perrin, Nobel Prize winner and Hulubei's mentor, endorsed moldavium as the true eka-caesium over Marguerite Perey's recently discovered francium. Perey took pains to be accurate and detailed in her criticism of Hulubei's work, and finally she was credited as the sole discoverer of element 87. [35] All other previous purported discoveries of element 87 were ruled out due to francium's very limited half-life. [36]
Eka-caesium was discovered on January 7, 1939, by Marguerite Perey of the Curie Institute in Paris, [34] when she purified a sample of actinium-227 which had been reported to have a decay energy of 220 keV. Perey noticed decay particles with an energy level below 80 keV. Perey thought this decay activity might have been caused by a previously unidentified decay product, one which was separated during purification, but emerged again out of the pure actinium-227. Various tests eliminated the possibility of the unknown element being thorium, radium, lead, bismuth, or thallium. The new product exhibited chemical properties of an alkali metal (such as coprecipitating with caesium salts), which led Perey to believe that it was element 87, produced by the alpha decay of actinium-227. [34] Perey then attempted to determine the proportion of beta decay to alpha decay in actinium-227. Her first test put the alpha branching at 0.6%, a figure which she later revised to 1%. [23]
Perey named the new isotope actinium-K (it is now referred to as francium-223) [34] and in 1946, she proposed the name catium (Cm) for her newly discovered element, as she believed it to be the most electropositive cation of the elements. Irène Joliot-Curie, one of Perey's supervisors, opposed the name due to its connotation of cat rather than cation; furthermore, the symbol coincided with that which had since been assigned to curium. [34] Perey then suggested francium, after France. This name was officially adopted by the International Union of Pure and Applied Chemistry (IUPAC) in 1949, [8] becoming the second element after gallium to be named after France. It was assigned the symbol Fa, but it was revised to the current Fr shortly thereafter. [39] Francium was the last element discovered in nature, rather than synthesized, following hafnium and rhenium. [34] Further research into francium's structure was carried out by, among others, Sylvain Lieberman and his team at CERN in the 1970s and 1980s. [40]
223Fr is the result of the alpha decay of 227Ac and can be found in trace amounts in uranium minerals. [9] In a given sample of uranium, there is estimated to be only one francium atom for every 1 × 1018 uranium atoms. [29] Only about 1 ounce (28 g) of francium is present naturally in the earth's crust. [41]
Francium can be synthesized by a fusion reaction when a gold-197 target is bombarded with a beam of oxygen-18 atoms from a linear accelerator in a process originally developed at the physics department of the State University of New York at Stony Brook in 1995. [43] Depending on the energy of the oxygen beam, the reaction can yield francium isotopes with masses of 209, 210, and 211.
The francium atoms leave the gold target as ions, which are neutralized by collision with yttrium and then isolated in a magneto-optical trap (MOT) in a gaseous unconsolidated state. [42] Although the atoms only remain in the trap for about 30 seconds before escaping or undergoing nuclear decay, the process supplies a continual stream of fresh atoms. The result is a steady state containing a fairly constant number of atoms for a much longer time. [42] The original apparatus could trap up to a few thousand atoms, while a later improved design could trap over 300,000 at a time. [7] Sensitive measurements of the light emitted and absorbed by the trapped atoms provided the first experimental results on various transitions between atomic energy levels in francium. Initial measurements show very good agreement between experimental values and calculations based on quantum theory. The research project using this production method relocated to TRIUMF in 2012, where over 106 francium atoms have been held at a time, including large amounts of 209Fr in addition to 207Fr and 221Fr. [44] [45]
Other synthesis methods include bombarding radium with neutrons, and bombarding thorium with protons, deuterons, or helium ions. [23]
223Fr can also be isolated from samples of its parent 227Ac, the francium being milked via elution with NH4Cl–CrO3 from an actinium-containing cation exchanger and purified by passing the solution through a silicon dioxide compound loaded with barium sulfate. [46]
In 1996, the Stony Brook group trapped 3000 atoms in their MOT, which was enough for a video camera to capture the light given off by the atoms as they fluoresce. [7] Francium has not been synthesized in amounts large enough to weigh. [8] [29] [47]
The alkali metals consist of the chemical elements lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs), and francium (Fr). Together with hydrogen they constitute group 1, which lies in the s-block of the periodic table. All alkali metals have their outermost electron in an s-orbital: this shared electron configuration results in their having very similar characteristic properties. Indeed, the alkali metals provide the best example of group trends in properties in the periodic table, with elements exhibiting well-characterised homologous behaviour. This family of elements is also known as the lithium family after its leading element.
Actinium is a chemical element; it has symbol Ac and atomic number 89. It was first isolated by Friedrich Oskar Giesel in 1902, who gave it the name emanium; the element got its name by being wrongly identified with a substance André-Louis Debierne found in 1899 and called actinium. Actinium gave the name to the actinide series, a set of 15 elements between actinium and lawrencium in the periodic table. Together with polonium, radium, and radon, actinium was one of the first non-primordial radioactive elements to be isolated.
Astatine is a chemical element; it has symbol At and atomic number 85. It is the rarest naturally occurring element in the Earth's crust, occurring only as the decay product of various heavier elements. All of astatine's isotopes are short-lived; the most stable is astatine-210, with a half-life of 8.1 hours. Consequently, a solid sample of the element has never been seen, because any macroscopic specimen would be immediately vaporized by the heat of its radioactivity.
The actinide or actinoid series encompasses at least the 14 metallic chemical elements in the 5f series, with atomic numbers from 89 to 102, actinium through nobelium. The actinide series derives its name from the first element in the series, actinium. The informal chemical symbol An is used in general discussions of actinide chemistry to refer to any actinide.
A chemical element is a chemical substance that cannot be broken down into other substances by chemical reactions. The basic particle that constitutes a chemical element is the atom. Chemical elements are identified by the number of protons in the nuclei of their atoms, known as the element's atomic number. For example, oxygen has an atomic number of 8, meaning that each oxygen atom has 8 protons in its nucleus. Two or more atoms of the same element can combine to form molecules, in contrast to chemical compounds or mixtures, which contain atoms of different elements. Atoms can be transformed into different elements in nuclear reactions, which change an atom's atomic number.
Caesium is a chemical element; it has symbol Cs and atomic number 55. It is a soft, silvery-golden alkali metal with a melting point of 28.5 °C, which makes it one of only five elemental metals that are liquid at or near room temperature. Caesium has physical and chemical properties similar to those of rubidium and potassium. It is pyrophoric and reacts with water even at −116 °C (−177 °F). It is the least electronegative element, with a value of 0.79 on the Pauling scale. It has only one stable isotope, caesium-133. Caesium is mined mostly from pollucite. Caesium-137, a fission product, is extracted from waste produced by nuclear reactors. It has the largest atomic radius of all elements whose radii have been measured or calculated, at about 260 picometers.
Mendelevium is a synthetic chemical element; it has symbol Md and atomic number 101. A metallic radioactive transuranium element in the actinide series, it is the first element by atomic number that currently cannot be produced in macroscopic quantities by neutron bombardment of lighter elements. It is the third-to-last actinide and the ninth transuranic element. It can only be produced in particle accelerators by bombarding lighter elements with charged particles. Seventeen isotopes are known; the most stable is 258Md with half-life 51.59 days; however, the shorter-lived 256Md is most commonly used in chemistry because it can be produced on a larger scale.
The periodic table, also known as the periodic table of the elements, is an ordered arrangement of the chemical elements into rows ("periods") and columns ("groups"). It is an icon of chemistry and is widely used in physics and other sciences. It is a depiction of the periodic law, which states that when the elements are arranged in order of their atomic numbers an approximate recurrence of their properties is evident. The table is divided into four roughly rectangular areas called blocks. Elements in the same group tend to show similar chemical characteristics.
Radium is a chemical element; it has symbol Ra and atomic number 88. It is the sixth element in group 2 of the periodic table, also known as the alkaline earth metals. Pure radium is silvery-white, but it readily reacts with nitrogen (rather than oxygen) upon exposure to air, forming a black surface layer of radium nitride (Ra3N2). All isotopes of radium are radioactive, the most stable isotope being radium-226 with a half-life of 1,600 years. When radium decays, it emits ionizing radiation as a by-product, which can excite fluorescent chemicals and cause radioluminescence.
Ununennium, also known as eka-francium or element 119, is a hypothetical chemical element; it has symbol Uue and atomic number 119. Ununennium and Uue are the temporary systematic IUPAC name and symbol respectively, which are used until the element has been discovered, confirmed, and a permanent name is decided upon. In the periodic table of the elements, it is expected to be an s-block element, an alkali metal, and the first element in the eighth period. It is the lightest element that has not yet been synthesized.
Tennessine is a synthetic chemical element; it has symbol Ts and atomic number 117. It has the second-highest atomic number and joint-highest atomic mass of all known elements, and is the penultimate element of the 7th period of the periodic table.
A period 6 element is one of the chemical elements in the sixth row (or period) of the periodic table of the chemical elements, including the lanthanides. 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 sixth period contains 32 elements, tied for the most with period 7, beginning with caesium and ending with radon. Lead is currently the last stable element; all subsequent elements are radioactive. For bismuth, however, its only primordial isotope, 209Bi, has a half-life of more than 1019 years, over a billion times longer than the current age of the universe. As a rule, period 6 elements fill their 6s shells first, then their 4f, 5d, and 6p shells, in that order; however, there are exceptions, such as gold.
In nuclear science, the decay chain refers to a series of radioactive decays of different radioactive decay products as a sequential series of transformations. It is also known as a "radioactive cascade". The typical radioisotope does not decay directly to a stable state, but rather it decays to another radioisotope. Thus there is usually a series of decays until the atom has become a stable isotope, meaning that the nucleus of the atom has reached a stable state.
A period 7 element is one of the chemical elements in the seventh row of the periodic 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 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, but there are exceptions, such as uranium.
Marguerite Catherine Perey was a French physicist and a student of Marie Curie. In 1939, Perey discovered the element francium by purifying samples of lanthanum that contained actinium. In 1962, she was the first woman to be elected to the French Académie des Sciences, an honor denied to her mentor Curie. Perey died of cancer in 1975.
Caesium perchlorate or cesium perchlorate (CsClO4), is a perchlorate of caesium. It forms white crystals, which are sparingly soluble in cold water and ethanol. It dissolves more easily in hot water.
Unbiunium, also known as eka-actinium or element 121, is a hypothetical chemical element; it has symbol Ubu and atomic number 121. Unbiunium and Ubu are the temporary systematic IUPAC name and symbol respectively, which are used until the element is discovered, confirmed, and a permanent name is decided upon. In the periodic table of the elements, it is expected to be the first of the superactinides, and the third element in the eighth period. It has attracted attention because of some predictions that it may be in the island of stability. It is also likely to be the first of a new g-block of elements.
Astatine compounds are compounds that contain the element astatine (At). As this element is very radioactive, few compounds have been studied. Less reactive than iodine, astatine is the least reactive of the halogens. Its compounds have been synthesized in nano-scale amounts and studied as intensively as possible before their radioactive disintegration. The reactions involved have been typically tested with dilute solutions of astatine mixed with larger amounts of iodine. Acting as a carrier, the iodine ensures there is sufficient material for laboratory techniques to work. Like iodine, astatine has been shown to adopt odd-numbered oxidation states ranging from −1 to +7.
Francium compounds are compounds containing the element francium (Fr). Due to francium being very unstable, its salts are only known to a small extent. Francium coprecipitates with several caesium salts, such as caesium perchlorate, which results in small amounts of francium perchlorate. This coprecipitation can be used to isolate francium, by adapting the radiocaesium coprecipitation method of Lawrence E. Glendenin and C. M. Nelson. It will additionally coprecipitate with many other caesium salts, including the iodate, the picrate, the tartrate, the chloroplatinate, and the silicotungstate. It also coprecipitates with silicotungstic acid, and with perchloric acid, without another alkali metal as a carrier, which leads to other methods of separation.
Radium compounds are compounds containing the element radium (Ra). Due to radium's radioactivity, not many compounds have been well characterized. Solid radium compounds are white as radium ions provide no specific coloring, but they gradually turn yellow and then dark over time due to self-radiolysis from radium's alpha decay. Insoluble radium compounds coprecipitate with all barium, most strontium, and most lead compounds.