The actinide or actinoid series encompasses the 14 metallic chemical elements with atomic numbers from 89 to 103, actinium through Lawrencium. 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.
Berkelium is a synthetic chemical element; it has symbol Bk and atomic number 97. It is a member of the actinide and transuranium element series. It is named after the city of Berkeley, California, the location of the Lawrence Berkeley National Laboratory where it was discovered in December 1949. Berkelium was the fifth transuranium element discovered after neptunium, plutonium, curium and americium.
Curium is a synthetic chemical element; it has symbol Cm and atomic number 96. This transuranic actinide element was named after eminent scientists Marie and Pierre Curie, both known for their research on radioactivity. Curium was first intentionally made by the team of Glenn T. Seaborg, Ralph A. James, and Albert Ghiorso in 1944, using the cyclotron at Berkeley. They bombarded the newly discovered element plutonium with alpha particles. This was then sent to the Metallurgical Laboratory at University of Chicago where a tiny sample of curium was eventually separated and identified. The discovery was kept secret until after the end of World War II. The news was released to the public in November 1947. Most curium is produced by bombarding uranium or plutonium with neutrons in nuclear reactors – one tonne of spent nuclear fuel contains ~20 grams of curium.
Californium is a synthetic chemical element; it has symbol Cf and atomic number 98. The element was first synthesized in 1950 at Lawrence Berkeley National Laboratory, by bombarding curium with alpha particles. It is an actinide element, the sixth transuranium element to be synthesized, and has the second-highest atomic mass of all elements that have been produced in amounts large enough to see with the naked eye. The element was named after the university and the U.S. state of California.
Einsteinium is a synthetic chemical element; it has symbol Es and atomic number 99. Einsteinium is a member of the actinide series and it is the seventh transuranium element. It was named in honor of Albert Einstein.
Fermium is a synthetic chemical element; it has symbol Fm and atomic number 100. It is an actinide and the heaviest element that can be formed by neutron bombardment of lighter elements, and hence the last element that can be prepared in macroscopic quantities, although pure fermium metal has not yet been prepared. A total of 20 isotopes are known, with 257Fm being the longest-lived with a half-life of 100.5 days.
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 days; however, the shorter-lived 256Md is most commonly used in chemistry because it can be produced on a larger scale.
Ionic radius, rion, is the radius of a monatomic ion in an ionic crystal structure. Although neither atoms nor ions have sharp boundaries, they are treated as if they were hard spheres with radii such that the sum of ionic radii of the cation and anion gives the distance between the ions in a crystal lattice. Ionic radii are typically given in units of either picometers (pm) or angstroms (Å), with 1 Å = 100 pm. Typical values range from 31 pm (0.3 Å) to over 200 pm (2 Å).
Few compounds of californium have been made and studied. The only californium ion that is stable in aqueous solutions is the californium(III) cation. The other two oxidation states are IV (strong oxidizing agents) and II (strong reducing agents). The element forms a water-soluble chloride, nitrate, perchlorate, and sulfate and is precipitated as a fluoride, oxalate or hydroxide. If problems of availability of the element could be overcome, then CfBr2 and CfI2 would likely be stable.
Berkelium forms a number of chemical compounds, where it normally exists in an oxidation state of +3 or +4, and behaves similarly to its lanthanide analogue, terbium. Like all actinides, berkelium easily dissolves in various aqueous inorganic acids, liberating gaseous hydrogen and converting into the trivalent oxidation state. This trivalent state is the most stable, especially in aqueous solutions, but tetravalent berkelium compounds are also known. The existence of divalent berkelium salts is uncertain and has only been reported in mixed lanthanum chloride-strontium chloride melts. Aqueous solutions of Bk3+ ions are green in most acids. The color of the Bk4+ ions is yellow in hydrochloric acid and orange-yellow in sulfuric acid. Berkelium does not react rapidly with oxygen at room temperature, possibly due to the formation of a protective oxide surface layer; however, it reacts with molten metals, hydrogen, halogens, chalcogens and pnictogens to form various binary compounds. Berkelium can also form several organometallic compounds.
Einsteinium(III) oxide is an oxide of the synthetic actinide einsteinium which has the molecular formula Es2O3. It is a colourless solid.
Niobium pentaiodide is the inorganic compound with the formula Nb2I10. Its name comes from the compound's empirical formula, NbI5. It is a diamagnetic, yellow solid that hydrolyses readily. The compound adopts an edge-shared bioctahedral structure, which means that two NbI5 units are joined by a pair of iodide bridges. There is no bond between the Nb centres. Niobium(V) chloride, niobium(V) bromide, tantalum(V) chloride, tantalum(V) bromide, and tantalum(V) iodide, all share this structural motif.
Curium(III) fluoride or curium trifluoride is the chemical compound composed of curium and fluorine with the formula CmF3. It is a white, nearly insoluble salt that has the same crystal structure as LaF3. It precipitates as a hydrate when fluoride ions are added to a weakly acidic Cm(III) solution; alternatively it can be synthesized by reacting hydrofluoric acid with Cm(OH)3. The anhydrous form is then obtained by desiccation or by treatment with hydrogen fluoride gas.
Neptunium(III) fluoride or neptunium trifluoride is a salt of neptunium and fluorine with the formula NpF3.
Neptunium(IV) fluoride or neptunium tetrafluoride is a inorganic compound with the formula NpF4. It is a green salt and is isostructural with UF4.
Einsteinium compounds are compounds that contain the element einsteinium (Es). These compounds largely have einsteinium in the +3 oxidation state, or in some cases in the +2 and +4 oxidation states. Although einsteinium is relatively stable, with half-lives ranging from 20 days upwards, these compounds have not been studied in great detail.
Praseodymium(III) iodide is an inorganic salt, consisting of the rare-earth metal praseodymium and iodine, with the chemical formula PrI3. It forms green crystals. It is soluble in water.
Californium(IV) oxide is a binary inorganic compound of californium and oxygen with the formula CfO
2.
Einsteinium fluoride is a binary inorganic chemical compound of einsteinium and fluorine with the chemical formula EsF3.
Curium(III) iodide is the chemical compound with the formula CmI3. Since all isotopes of curium are only artificially produced, the compound has no natural occurrence.
