Francium (Fr) | AMERICAN ELEMENTS ® Isotopes About Francium Francium is the second rarest and the most unstable naturally occurring element on the periodic table; only astatine is rarer. A product of a disintegration of actinium , which undergoes beta-disintegration 99% of the time, francium is so highly radioactive that its most stable isotope (Francium-233, formerly known as actinium-K) has a half-life of merely 22 minutes. As such, only 20-30 grams of the element are present at any given time in the earth’s crust, limited to trace amounts in uranium and thorium ores. Francium can be produced in the laboratory via bombardment of thorium with protons or radium with neutrons, but only in small quantities--the largest amount ever synthesized was a cluster of 30,000 atoms. The element has never been observed in bulk; with the lowest electronegativity of any element on the periodic table, it would immediately vaporize due to the extreme heat of decay. Thus, scientists estimate that francium’s theoretical properties are similar to the other members of the alkali metals family .

There are no commercial applications for francium because of its instability. Dmitri Mendeleev predicted the existence of Francium in the 1870's, calling it “eka-caesium” because of its similarity to cesium (“eka” meaning one element down on the periodic table). The element was discovered by French chemist Marguerite Catherine Perey of the Curie Institute in 1939 while analyzing the decay of actinium ; named for her country of origin, Francium would become the last naturally-occurring element to be discovered rather than being synthesized in a laboratory. Francium Properties Francium is a S-Block, Group 1, Period 7 element. The number of electrons in each of Francium's shells is 2,8,18,32,18,8,1 and its electronic configuration is 1s2 2s2p6 3s2p6d10 4s2p6d10f14 5s2p6d10 6s2p6 7s1. In its elemental form francium's CAS number is 7440-73-5.

The francium atom has a radius of 270.pm and it's Van der Waals radius is 348.pm. Francium was discovered by Marguerite Perey of the Curie Institute in Paris, France in 1939 although its existence was predicted by Mendeleev during the 1870's. Francium, formerly known as eka-caesium and actinium K, is the second rarest naturally occurring element, the first being Astatine . Francium has the lowest electronegativitiy of all known elements and it was the last element discovered in nature. Outside of the laboratory, only trace amounts of francium can be found in uranium and thorium ores. Out of all of the naturally occurring elements, francium is the most unstable. Due to its rarity and instability, commercial applications for francium do not exist. Francium information, including technical data, properties, research, and other useful facts are discussed below. Scientific facts such as the atomic structure, ionization energy, conductivity and thermal properties are also included.

smart-elements� - Buy Francium online Year: 1939 Francium formerly known as eka-caesium and actinium K, is a chemical element that has the symbol Fr and atomic number 87. It has the lowest known electronegativity of all known elements, and is the second rarest naturally occurring element (after astatine). 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 synthesized. 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 30 g (one ounce) exists at any given time throughout the Earth's crust; the other isotopes are entirely synthetic.

The largest amount ever collected of any isotope was a cluster of 10,000 atoms (of francium-210) created as an ultracold gas at Stony Brook in 1997. Views: 53132 What does Francium mean? Definitions for Franciumˈfræn si əm This page provides all possible meanings and translations of the word Francium Princeton's WordNet(0.00 / 0 votes)Rate this definition: francium, Fr, atomic number 87(noun) a radioactive element of the alkali-metal group discovered as a disintegration product of actinium Wiktionary(1.00 / 1 vote)Rate this definition: francium(Noun) A metallic chemical element (symbol Fr) with an atomic number of 87. Origin: From francium, from (after the native country of . Freebase(0.00 / 0 votes)Rate this definition: Francium Francium is a chemical element with symbol Fr and atomic number 87. It was formerly known as eka-caesium and actinium K. 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. Bulk francium has never been viewed. Because of the general appearance of the other elements in its periodic table column, it is assumed that francium would appear as a highly reflective metal, if enough could be collected together to be viewed as a bulk solid or liquid. However preparing such a sample is impossible, since the extreme heat of decay would immediately vaporize any viewable quantity of the element. Francium was discovered by Marguerite Perey in France in 1939. It was the last element discovered in nature, rather than by synthesis. 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 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. U.S.

National Library of Medicine(0.00 / 0 votes)Rate this definition: Francium Francium. A radioactive alkali metal with the atomic symbol Fr, atomic number 87, and atomic weight 223. The mass numbers of other known isotopes are 204-213, 217-222, and 224. Its valence is +1. Numerology The numerical value of Francium in Chaldean Numerology is: 3 Pythagorean Numerology Giving: Department of Chemistry, College of Arts and Sciences, Syracuse University Hydrogen (H) -- The most abundant of all elements, making up more than 90% of all atoms; the lightest of all gases, combines with other elements, sometimes explosively, to form compounds. Rocket fuel, hydrogenation of fats, water, and ammonia. Sponsor: Bruce Hudson Helium (He) -- Lowest melting point of any element; used as an inert gas shield for welding and a lifting gas for balloons. Balloons, blimps, diving bell atmosphere, lasers, leak detectors, and nuclear plant coolant.

Lithium (Li) -- The lightest of all metals, found in small amounts in igneous rock and in the waters of mineral springs; used as an alloying agent. Pharmaceuticals, glass, pacemaker batteries, alloys used in space, and lubricant additive. Beryllium (Be) -- Steel gray, one of the lightest metals; used in high-speed aircraft, missiles and spacecraft. Watch springs, X-ray tube windows, spark-free tools, and heat conducting ceramics. Boron (B) -- Element with interesting optical properties; a boron compound, borax, is used as a water softener in powdered detergents. Heat resistant glass, regulators in nuclear plants, eye disinfectant. Carbon (C) -- The basis for life; a truly unique element that takes forms ranging from diamonds to lumps of coal. Pencils, diamonds, coal, tire colorant, steel, plastics, life. Sponsor: Phillip M. Pivawer Nitrogen (N) -- Makes up 78% of the air, with more than 4000 billion tons in the atmosphere; compounds important in foods, poisons, fertilizers, and explosives.

Refrigerant, coolant (liquid nitrogen), cryogenic surgery, ammonia production, rocket fuels. Oxygen (O) -- The third most abundant element found in the universe; essential for respiration of all plants and animal and for practically all combustion. Hospital life support, combustion, steel production, water purification. Sponsor: Gershon and Dina Vincow Fluorine (F) -- The most electronegative and reactive of all elements; a pale yellow, corrosive gas; used in drinking water to prevent dental decay. Toothpaste additives, uranium enrichment, refrigerator coolants, Teflon. Neon (Ne) -- A rare gaseous element that glows reddish-orange in a vacuum discharge tube; used in making advertising signs, high-voltage indicators, lightning arrestors, and TV tubes. Neon lights, fog lights, TV tubes, lasers, voltage detectors. Sodium (Na) -- Bright, soft, silvery metal; very reactive and never found free in nature; compounds used in paper, glass, soap, textile, petroleum, chemical and metal industries; ingredient in kitchen salt, soda, glass, street lights, batteries, nuclear reactor coolant.

Magnesium (Mg) -- A light, silvery white metal that readily ignites upon heating in air and burns with a dazzling white flame; used in flash photography, flares and fireworks and as an alloy with aluminum. Sparklers, chlorophyll, airplanes, bricks for fireplaces. Aluminum (Al) -- Silvery white metal. Thousands of household and industrial applications. Planes, cars, rockets, window frames, doorknobs, tube, cable, foil, fireworks, flash bulbs. Sponsor: Dr. Lisa D. Coutts Silicon (Si) -- One of the most useful elements, in different forms used to make brick, glass, electron devices; present in human skeleton. Solar cells, micro chips, tools, quartz, cement, glass, silicon rubbers and oils. Phosphorus (P) -- Widely distributed in combination with other minerals; an essential component of all cell protoplasm, nervous tissue and bones; spontaneously combusts in air. Matches, fireworks, fertilizers, detergents, toothpastes, pesticides.

Sulfur (S) -- A pale yellow, odorless, brittle solid; found in meteorites and naturally occurs near volcanoes and hot springs; component of gun powder, is used to cure rubber and as a fungicide. Odorant for natural gas, matches, fireworks, batteries, vulcanization of rubber. Chlorine (Cl) -- Greenish-yellow gas that combines directly with most elements, used in making many everyday products; used to produce safe drinking water. Bleach, hydrochloric acid, water purification, plastics, stain removers. Argon (Ar) -- Gas present in air; makes up 0.94% of the atmosphere. Lasers, geiger counters, light bulbs, gas discharge tubes, welding blanket gas. Potassium (K) -- Alkaline metal never found free in nature; used in fertilizers; spontaneously combusts in water. Glass lenses, fertilizer, matches, gun powder, salt substitute. Essential constituent of leaves, bones, teeth and shells. Concrete, plaster of Paris, fertilizer, metallurgy, bones. Sponsor: Prof. Robert R. Birge, Mrs. Constance R.

Birge Scandium (Sc) -- Soft, silvery-white metal found in residues of rare earth metals; is much more abundant in the sun and stars than here on earth. Stadium lighting, leak detectors, large screen TVs. Titanium (Ti) -- A lustrous white metal that is present in meteorites and in the sun, in igneous rocks and in their sediment. Bone pins, heat exchanger, airplane motors, pigments for paint and paper. Vanadium (V) -- Bright white metal that is soft and ductile with good structural strength; used in the production of steels for tools and in nuclear applications. Tools, construction materials, springs, jet engines. Chromium (Cr) -- Lustrous, steel-gray, hard metal, much of which is used in plating to produce a hard, beautiful surface and to prevent corrosion. Camouflage paints, lasers, stereo, video tapes, tools, knives, plating for car parts. Manganese (Mn) -- A gray-white metal resembling iron that is used to form many alloys; in steel, improves strength, toughness, stiffness, wear resistance and hardening; also used in dry cell batteries.

Plows, safes, steel for rail switches, tools, axes, batteries. Iron (Fe) -- Relatively abundant in the universe; a major component of meteorites; the cheapest, most abundant, useful and important of all metals. Magnets, machines, bikes, cars, bridges, nails, tools, red blood cells. Sponsor: LighTouch Medical Cobalt (Co) -- A brittle, hard metal that resembles iron and nickel; in salts has been used for centuries to produce brilliant blue color in pottery, tiles and enamels. Permanent blue pigment, razor blades, permanent magnets, catalytic converters. Nickel (Ni) -- A constituent in most meteorites, often used to distinguish meteorites from other minerals; silvery-white metal that takes on a high polish; valuable as an alloy. Coins, knives, forks, spoons, crucibles, white gold, rechargeable batteries. Copper (Cu) -- One of the world's most important metals; used especially in electrical industry and in the alloys bronze and brass; all American coins are copper alloys. Statue of Liberty, cable, wire, water pipe, pennies, bronze sculpture, bells, carillons.

Zinc (Zn) -- Bluish-white, lustrous metal used for making brass; also used to produce nickel silver, commercial bronze, spring brass, German silver, soft solder and aluminum solder; used in production of paints, rubber, and cosmetics. Corrosion resistant coating, water and gas valves, batteries, gutters, white pigments in rubber. Gallium (Ga) -- A metal that is liquid near room temperatures; gallium arsenide is used as a compound semiconductor used to fabricate electron devices. Infrared night vision, computer memory, quartz thermometers, transistors, laser diodes. Germanium (Ge) -- A gray-white metalloid element and important semiconductor material used in transistors, as an alloying agent, as a phosphor in fluorescent lamps, and as a catalyst. Fiber optics, infrared night vision, wide-angle lenses, semiconductors. Arsenic (As) -- Element that appears in white, gray and yellow solid forms; poisonous murder weapon favored by mystery writers. Shotgun pellets, metal for mirrors, glass, lasers, light emitting diodes (LEDS).

Selenium (Se) -- A member of the sulfur family; can be red, in powder form, or black, in vitreous form; exhibits both photovoltaic action and photo-conductive action make possible its use in photographic equipment; used to color glass and enamels. Copy machines, light meters, solar cells, dandruff shampoos. Bromine (Br) -- The only liquid non-metallic element, with a strong, disagreeable odor; one form used in gasoline anti-knock compounds. Fire retardants, photographic film, tear gas, disinfectants. Sponsor: Roger and Estelle Hahn Krypton (Kr) -- A rare, inert gas present in the air at about one part per million. Atomic clocks, fluorescent bulbs, flash bulbs, UV lasers. Rubidium (Rb) -- Soft, silvery white metallic element of the alkali group; ignites spontaneously in air and reacts violently in water, setting fire to the liberated hydrogen. Heart muscle research, photoelectric cells, gas scavenger in vacuum tubes. Strontium (Sr) -- A metal which, finely divided, ignites spontaneously in air; salts used in fireworks for the crimson color of their flames.

Nuclear batteries in buoys, beta radiation source, phosphorescent paint. Yttrium (Y) -- Silvery element that occurs in most rare earth metals; turnings of the metal ignite in air; used in alloys with aluminum, magnesium and iron. Color TV screens, radar, lasers, superconductors, fireproof bricks. Zirconium (Zr) -- Grayish-white, lustrous metal that is exceptionally resistant to corrosion; when finely divided, will ignite in air; used in poison ivy lotion. Zircon gemstone, nuclear fuel rods, catalytic converters, furnace bricks. Niobium (Nb) -- A shiny, white, soft metal that takes on a bluish cast when exposed to air at room temperatures for a long time; used as an alloy. Welding rods, cutting tools, pipelines, superconducting magnets. Molybdenum (Mo) -- A metal at first confused with lead and graphite; used in many alloys and in missile and aircraft parts; an essential trace element in plant nutrition. Filament in electric heaters, rocket motors, lubricants, source of radio isotopes.

Technetium (Tc) -- A silver-gray metal that tarnishes slowly in moist air; the first element to be produced artificially; a corrosion inhibitor for steel. Radiation source for medical research. Sponsor: Molecular Insight Pharmaceuticals Ruthenium (Ru) -- Metallic element found in residue from platinum ore; an effective hardener for platinum and palladium. Eye treatment, surgery, thickness meters for eggshells, fountain pen point. Rhodium (Rh) -- Metallic element often found with platinum metals, useful as an electrical contact material; has a high reflectance and durability; sometimes used in jewelry. Headlight reflectors, telephone relays, airplane spark plugs, catalytic converters. Palladium (Pd) -- Element found along with metals of the platinum group, a steel-white metal alloyed with gold to form white gold; used in dentistry, watch making, surgical instruments and electrical contacts. Dental, catalytic converters, hydrogen separation, anti-tumor. Silver (Ag) -- Metal known since ancient times, prized for its brilliant white luster; alloys used in jewelry, coins, and dentistry; also important in photography. Silverware, mirrors, batteries, photographic film, paper, photosensitive glass.

Cadmium (Cd) -- A soft, bluish-white element that is easily cut with a knife; used in batteries and electroplating; toxic. Rechargeable batteries, red and yellow pigments, plating of screws, bolts, regulator in nuclear reactors. Indium (In) -- A very soft, silvery-white metal; used in making bearing alloys, germanium transistors, photoconductors, and mirrors. Transistors, photo cells, solar cells, mirrors, regulator in nuclear power, clear conductive coatings. Tin (Sn) -- A silvery white metal with a highly crystalline structure; used to coat other metals to prevent corrosion; important in alloys like solder, pewter, and bronze. Organ pipes, pewter cups and plates, opalescent glass, enamel, weather resistant vinyl siding. Antimony (Sb) -- Common metallic element that increases strength of lead. Ceramic glass, solder, type for printing, lead batteries, fire retardants. Tellurium (Te) -- Silvery white element with a metallic luster; is brittle and easily pulverized; most often found as the telluride of gold and other metals; important semiconductor.

Vulcanization of rubber, percussion caps, battery plate protector, electrical resistors. Sponsor: Donald C. Dittmer Iodine (I) -- A grayish black, lustrous solid that volatizes at ordinary temperatures into a blue-violet gas with an irritating odor; used in different forms to treat thyroid disease and cleanse wounds, and in the photographic process. Photographic film, ink pigments, salt additive, disinfectant, halogen lamps. Xenon (Xe) -- Inert gas present in the atmosphere at about one part in 20 million; in a vacuum tube, produces a beautiful blue glow when excited by an electrical discharge. Sun lamps, UV lamps, paint testers, projection lamps, electronic flashes. Cesium (Cs) -- Silvery white, soft alkaline metal that is liquid at room temperature; reacts explosively with cold water. Atomic clock, photoelectric cells, gamma radiation source, scintillation counters. Barium (Ba) -- Soft, silver-white metallic element from the alkaline earth group; sulfate used in paint, x-ray diagnostic work, and glass making. Fireworks (green), magnetic recording tapes, gas scavenger in vacuum, fluorescent lamps.

Lanthanum (La) -- A silvery white, malleable, ductile rare earth metal that oxidizes rapidly when exposed to air; compounds used in carbon lighting applications, especially by the film industry for studio lighting and projection. Camera lenses, battery electrodes, catalytic converters, lighter flints. Cerium (Ce) -- The most abundant of the rare earth metals; used in carbon-arc lighting in the film industry. Lighter flints, catalytic converters, kluge lights, self cleaning ovens. Praseodymium (Pr) -- Soft, silvery and malleable rare earth metal; used in carbon arcs for lighting in film industry; salts are used to color glass and enamels yellow. Cryogenic refrigeration, permanent magnets, search lights, ceramic cooling. Neodymium (Nd) -- A bright silvery metallic rare earth metal; used to color glass a light lavender and as a laser material. High strength magnets for disc drives, coloring for eyeglasses, ceramic capacitors, glass for lasers and lenses.

Promethium (Pm) -- Beta radiation source for thickness gauges, source for signals that require dependable operation (using phosphor to absorb the beta radiation and produce light), nuclear battery in which photocells convert the light into electric current. Samarium (Sm) -- A rare earth metal with a bright silver luster; used for carbon-arc lighting for the film industry; oxide used in infrared absorbing glass and as a neutron absorber in nuclear reactors. Ceramic capacitors, high temperature permanent magnets, lasers. Europium (Eu) -- A silvery white element with a metallic luster identified spectroscopically in the sun and certain stars. Color TV tubes, X-ray intensifier screens, mercury lamps, energy saving trichromatic fluorescent lights. Gadolinium (Gd) -- A silver-white, malleable rare earth metal; useful in nuclear rods and possibly as nuclear shields; has unusual superconducting properties. Diagnosing osteoporosis, permanent magnets, X-ray tubes, computer memory. Terbium (Tb) -- Silvery gray, rare earth metal, relatively stable in air; used in solid-state devices.

Magneto-optic alloys for CDs, X-ray screens, fluorescent lamps, magnetic-strictive alloys for submarine transducers. Dysprosium (Dy) -- A rare earth metal with a bright silver luster. Magneto-optic alloys for CDs, X-ray screens, color TV tubes, mercury lamps, neutron scavenger. Holmium (Ho) -- A rare earth metal that in its pure form has a metallic to bright silver luster; relatively soft and malleable. Glass coloring, eye-safe lasers. Erbium (Er) -- A dark gray metallic powder with nuclear and metallurgical applications; in oxide form gives a pink color used in glasses and porcelain enamel glazes. Glass coloring, infrared fiber optics, coating for sun glasses, pink simulant gemstones. Bright, silvery metal, the least abundant of the rare earth elements. Lasers. Ytterbium (Yb) -- Rare earth metal with a bright, silvery luster; soft and malleable. Dentures, portable X-ray source for blood treatment, carbon arc lamps.

Lutetium (Lu) -- A rare earth metal that occurs in small amounts in nearly all minerals containing yttrium; one of the most costly of all elements. Temperature sensing optics. Hafnium (Hf) -- Along with zirconium, one of the hardest elements to separate; has a brilliant silver luster; used in nuclear reactor control rods. Nuclear submarines, controls nuclear reactions, gas scavenger in vacuum tubes. Tantalum (Ta) -- A gray, heavy, hard metal with a high melting point; used in a variety of alloys; used in surge suppressors, chemical process equipment, nuclear reactors, aircraft and missile parts, and surgical equipment. Weights, capacitors, vacuum tube filaments, cutting tools. Tungsten (W) -- Steel-gray to white element; in pure and alloy form used for electric light filaments, x-ray targets, space missile and high-temperature applications. Lamp filaments, welding electrode, rocket nozzles, cutting and boring tools.

Rhenium (Re) -- Metallic element often found in platinum ores; used as an additive to tungsten and molybdenum-based alloys; used as electrical contacts, filaments for mass spectrographs and gages, thermocouples, and flash lamps for photography. Electrodes, oven filaments, jewelry plating, thermocouples. Osmium (Os) -- Lustrous, blue-white hard metal; used in various forms to detect fingerprints, stain fatty tissue for microscope slides, and to produce hard alloys. Fountain pen points, decorations, compass needles, clock bearings. Iridium (Ir) -- A metal of the platinum family, white with a yellowish cast, hard and brittle, the most corrosion-resistant metal known; used as a hardening agent for platinum. Helicopter spark plugs, hypodermic needles, satellite thruster engines. Platinum (Pt) -- A beautiful, silvery-white metal extensively used in jewelry, wire and vessels for laboratory use, thermocouple elements, electrical contacts and dentistry. Crucibles, dental crowns, anti-tumor agents, catalyst for nitric acid products.

Gold (Au) -- The most beautiful of all elements; when in a mass this metal is yellow, but when finely divided may be black, ruby or purple. Jewelry, precious metals, electrical contacts, dental crowns. Mercury (Hg) -- The only common metal that is liquid at room temperature; used in laboratory instruments, mercury-vapor lamps, pesticides, batteries, and catalysts. Thermometers, barometers, street lights, thermostats, dental fillings, seed protection. Thallium (Tl) -- A soft, malleable and toxic metal; when freshly exposed to air has a metallic luster, but rapidly develops a bluish-gray tinge. Insecticides, thermometer filling, infrared detectors, heat muscle research. Lead (Pb) -- Bluish-white with a bright luster, very soft; very effective as a sound and vibration absorber and a radiation shield. Radiation protection, roof coverings, batteries, solders, ammunition, crystal stemware, fishing weights. Bismuth (Bi) -- White, crystalline, brittle metal with a pinkish tinge; in early times was confused with tin and lead.

Antacids, antidiarrheals, catalyst in rubber production. Polonium (Po) -- A very rare, natural, radioactive element, the first discovered by Marie Curie; can be mixed or alloyed with beryllium. Nuclear batteries, neutron source, antistatic agents, film cleaner. Radioactive element; isotopes have very short half-lives. Seldom found in nature. Radon (Rn) -- The heaviest known gas, naturally occurring in soil; at normal temperatures is colorless, but when cooled below freezing, exhibits a brilliant phosphorescence that becomes yellow and then orange-red as the temperature is lowered. Health threat in home built on granite, earthquake meter, seldom found in nature. Francium (Fr) -- The last member of the alkali metal series; there is probably less than an ounce of Francium at any time in the total crust of the earth. Seldom found in nature. Radium (Ra) -- Radioactive element discovered by Pierre and Marie Curie, the study of which has greatly altered ideas of the structure of the atom; used to produce luminous paints, neutron sources and in medicine for the treatment of disease. Antique glow in the dark paint, neutron source.

150 times as radioactive as radium; of value in production of neutrons. Neutron source. Thorium (Th) -- Silvery-white, radioactive metal; when heated in air, ignites and burns brilliantly with a white light; used for portable gas lights, alloying material with magnesium, and for high-temperature crucibles. Coating on filament wire, breeder reactor fuel, gaslight mantles, crucibles. Protactinium (Pa) -- Radioactive element that has a bright metallic luster; isotopes have very long half-lives. Trace contaminant in ceramic glazes. Uranium (U) -- Heavy, silvery white, radioactive metal of great importance as a nuclear fuel. Breeder reactor fuel, nuclear reactor fuel, gyro compasses, glass coloring. Neptunium (Np) -- A synthetic transuranium element with a silvery appearance; isotope used as a component in neutron-detection instruments. Plutonium (Pu) -- A transuranium element used as an explosive ingredient in nuclear weapons and nuclear power; radiological poison that must be specially handled.

Americium (Am) -- Radioactive element, identified as the result of successive neutron capture reactions by plutonium isotopes in a nuclear reactor. Crystal research, smoke detectors, glass thickness meters, neutron source. Radioactive element discovered in 1958; attempts to duplicate experiment have failed. Lawrencium (Lr) -- Last of the actinide series to be discovered, based solely on nuclear rather than chemical evidence. Rutherfordium (Rf) -- Not used for anything and little is known about it. Rutherfordium is the first transactinide element and it is predicted to have chemical properties similar to hafnium. Dubnium (Db) -- Formerly called Hahnium, named after Dubna, the city that contains the Russian Joint Institute for Nuclear Research. Seaborgium (Sg) -- Chemistry resembles that of tungsten, discovered almost simultaneously by two different laboratories, Joint Institute for Nuclear Research at Dubna and the Lawrence Radiation Laboratory at the University of California, Berkeley. Bohrium (Bh) -- Synthesized in 1976 by a Soviet team led by Y. Oganessian at the Joint Institute for Nuclear Research at Dubna.

Hassium (Hs) -- First synthesized in 1984 at the Institute for Heavy Ion Research in Darmstadt, Germany. Name derived from the Latin name for the German state of Hessen where the institute is located. Barely Radioactive Elements Barely Radioactive Elements Original image by Heinrich Pniok ( ) licensed under the Creative Commons Attribution-ShareAlike 3.0 (CC-BY-SA-3.0) license. If you ask somebody who remembers a bit of their high school chemistry, “What's the heaviest stable (non-radioactive) element?” they'll usually answer “ Lead .” If you pose the same question to a chemist, they'll probably glance at the periodic table on the wall and respond “ Bismuth .” Reality is somewhat more complicated, and interesting in its details. The chemist is correct in noting that all elements heavier than bismuth (element 83) have no stable isotopes, and only a few which have isotopes with very long half-lives such as thorium and uranium occur in substantial quantities in nature.

(Others, such as polonium and radon , are found in nature as daughter products from the decay of thorium and uranium but are not primordial [left over from the formation of the solar system].) But is bismuth actually stable? Naturally occurring bismuth is composed exclusively of the isotope bismuth-209 (209Bi), whose atoms contain 83 protons and 126 neutrons. Now, nuclear structure is quite well understood, and it is possible to calculate from theory that the bismuth-209 nucleus is in a higher energy state than the sum of the energies of a nucleus of thallium-205 and an alpha particle (nucleus of helium-4 ). In quantum mechanics, whatever is not forbidden by a conservation law must happen eventually, and since alpha decay of bismuth-209 to thallium-205 does not violate conservation of energy or any other law, it has long been expected to occur, but had not been observed to happen.

This all changed in 2003, when a group of researchers at the Institut d'Astrophysique Spatiale in Orsay, France reported in a paper in Nature the direct detection of alpha particles resulting from the decay of bismuth-209 using a detector cooled to just two hundredths of a degree above absolute zero (20 mK). They were able to calculate the half-life of bismuth-209 as 1.9×1019 years. This is a long time. How long? Well, the universe is about 1.38×1010 years old (time from the big bang to the present), so the half-life of bismuth-209 (henceforth I'll write just “bismuth” as this is the only naturally-occurring isotope) is about a billion (109) times the age of the universe.

Based upon our understanding of astrophysics and the process of star formation in galaxies, all of the stars in the universe will have burned out in around 1014 years, so you'll have to wait a time a hundred thousand times longer than the era in which stars shone in the universe for half of the bismuth atoms in your bottle of Pepto-Bismol to decay away, which probably substantially postdates the “use before” date on the label. What will the universe be like 1019 years in the future? Well before the last stars burn out at 1014 years, all of the galaxies in the Local Group will have merged into one enormous galaxy. The inexorable acceleration of the expansion of the universe due to dark energy will red-shift even the most energetic radiation from other superclusters of galaxies to wavelengths longer than the size of the observable universe by around 2×1012 years: astronomers in that distant epoch will observe only a single galaxy in an otherwise entirely empty universe . If reports of observations of the universe from our era remain, one wonders whether anybody would believe them.

By around 1015 years, planets which orbit the burned-out remains of stars (this being a time ten times longer that that in which stars shone) will be ejected from their orbits by encounters with other stellar remnants or crash into and merge with their own central body due to orbital decay by gravitational radiation . And after an interval ten thousand times longer than this, half the bismuth will still be around. Let's look through the other end of the telescope and see how radioactive bismuth really is. Radioactive decay is governed by the equations: where t½ is the-half life, λ the decay constant, τ the mean lifetime, N the number of particles in the sample, and A the number of decays per unit time (using the same time unit as half-life). Let's assume we have a one gram sample of bismuth: a cube about half a centimetre on a side. The atomic weight of bismuth is around 209, so our one gram sample is 1/209 mole . A mole of any substance is composed of Avogadro's number , 6.022×1023 of constituents.

Dividing this by 209, we find our sample contains 2.9×1021 atoms of bismuth. Using the formulæ above, we find that 105 atoms of bismuth in our sample will decay, on average, every year, or around one every three and a half days. But these are alpha decays. Alpha particles have very little penetrating power—a sheet of paper or human skin completely stops them, and bismuth is a heavy element with far greater absorption than those light substances. So, in terms of alpha particles emitted from these rare decays, only those which occur very near the surface will ever be emitted outside the sample: all the rest will be trapped inside. As the overwhelming bulk of a macroscopic sample is in the volume, not on the surface, emitted alpha particles will be correspondingly rare. The French team who measured the decay rate employed the clever strategy of using a detector which was a compound including bismuth and germanium , so that almost every decay would result in a signal from the detector. Getting back to the original question, was the non-professional's guess that lead is the heaviest stable element correct? Well, not so fast….

Naturally occurring lead is composed of four isotopes: lead-204, lead-205, lead-207, and lead-208, with the latter making up more than half. From the same energetic calculation which caused nuclear chemists to suspect that bismuth was slightly radioactive, each of these nuclides should be exothermic to alpha decay with very long half-lives. No such decays have ever been observed experimentally, so only a lower bound on their half-lives, on the order of that of bismuth, can be given. From a theoretical and experimental standpoint thallium (element 81) is believed to be absolutely stable. Still, when it comes to barely radioactive elements, bismuth doesn't take the prize.

Barium -130 decays into xenon-130 through the process of double electron capture with a half-life of 0.5–2.7×1021 years, around a hundred times that of bismuth, and tellurium -128 is the all time champion, decaying into xenon -128 by double beta decay with a half-life of 2.2×1024 years. This, the longest experimentally-measured half-life at this writing, is a hundred thousand times longer than that of bismuth, and 160 trillion times the present age of the universe. If you had a one gram sample of pure tellurium-128 (which would be expensive to prepare, since you'd have to perform isotope separation to isolate the 128Te, which makes up about a third of naturally-occurring tellurium), you'd only observe a decay event on average once every 674 years. In wilder realms of speculation, some grand unified theories of particle physics predict that the proton, and by implication, all elements should eventually decay.

Experiments have shown that proton decay, if it occurs, must have a half-life in excess of 1033 years, more than 50 trillion times longer than that of bismuth and 72 billion trillion times the present age of the universe. You may wonder which naturally-occurring element has the shortest half-life. That would be francium , element 87, whose longest-lived isotope, francium-223, has a half-life of 22 minutes, decaying either into radium by beta decay or astatine by alpha emission. It was discovered in nature in 1939 (the last radioactive element to be found in nature rather than by synthesis) and is present in trace amounts in uranium and thorium ores. At any given time, it is estimated that only 20–30 grams of francium are present in the Earth's crust. All elements from hydrogen to californium (element 98) have been found in nature, but most of the radioactive elements were first discovered by synthesis and then later detected in trace amounts in natural uranium ore. There is a distinction between “found in nature” and primordial .

While the first 98 elements are found in nature, only 84 have atoms present in nature which date from the formation of the solar system. Of these, 80 are stable and four (bismuth, thorium, uranium, and plutonium) are radioactive.

Question: The last element to be discovered in nature, rather than synthesized, was discovered In 1939. What was it?
Answer: Francium