Rhenium

Rhenium is a very rare metal that was discovered in 1925 by Otto Berg, Ida Noddack and Walter Noddack. It has several distinct characteristics and is widely used in making of superalloys.

History and Discovery

Rhenium was discovered in 1925 by Otto Berg, Ida Noddack and Walter Noddack from ores of platinum and in various minerals. They also succeeded in extracting pure form of rhenium in 1928. The element was named Rhenium after a river in Europe, called Rhine. In order of discovery among elements, rhenium was the second last stable element [1].

Rhenium

Periodic Table ClassificationGroup 7
Period 6
State at 20CSolid
ColorSilvery-grayish
Electron Configuration[Xe] 4f14 5d5 6s2
Electron Number75
Proton Number75
Electron Shell2, 8, 18, 32, 13, 2
Density21.04 g.cm-3 at 20°C
Atomic number75
Atomic Mass186.21 g.mol -1
Electronegativity according to Pauling1.90

Occurrence

Rhenium is extremely rare and is considered as the rarest of all metals. it is found in about 0.5 ppb of Earth’s crust and is ranked as the 77th most abundant element in the Earth’s crust [2]. Rhenium does not exist in native form. The ores and minerals of rhenium are also quite and molybdenite and gadolinite are some of the minerals that contain trace amount rhenium. Rhenium is an expensive metal as it has a high demand and low availability. The largest producer of rhenium in the world is Chile, where the largest copper ore deposits of rhenium are found. Recently, a mineral of rhenium, rheniite (ReS2), is being used for extracting large amount of rhenium (20-60 kg rhenium per year) [3]. Other countries that are leading producers of rhenium include Peru, USA and Poland.

Physical Characteristics

Rhenium is a greyish silver metal. Rhenium has remarkably high boiling point (5627 °C) and is categorized as the element with the highest boiling point. It also has one of the highest melting point (3170 °C), second only to carbon and tungsten. Rhenium is a significantly dense metal (21.02 g/cm3). Rhenium do not dissolve in acids and alkalis at room temperature. It does not dissolve in aqua regia.  Rhenium is resistant to tarnishing and is corroded very slowly in the presence of moist air. The atomic number of rhenium is 75 and its atomic mass is 186.

Chemical Characteristics

Rhenium is not very reactive metal. It exists in many oxidation states in compounds, and +2, +4, +6 and +7 are the most common [4]. Rhenium is used in powder form. Rhenium is unreactive with water at standard conditions. Some salts of rhenium have commercial importance, such as sodium perrhenates and ammonium perrhenates. Rhenium forms oxide and the most common is rhenium (VII) oxide, which is a colorless and volatile compound. Rhenium also from various organic compounds, such as dirhenium decacarbonyl, methyl-rhenium trioxide and pentacarbonylhydridorhenium.

Significance and Uses

  • Rhenium is a widely used super alloy. It is used to make alloys with various metals to impart desirable characteristics. Rhenium is widely used to make high-temperature superalloys, that are used for manufacturing of parts of military jet engines.
  • Rhenium is used as catalyst in gasoline, in combination with platinum.
  • Rhenium superalloys are used in gas turbine engines in various industries.
  • Rhenium is used in making electrical contact points, mass spectrometers and photographic flash lamps.
  • Rhenium tungsten superalloys are used in making X-ray machines.
  • Rhenium isotopes (rhenium-186 and 188) are used to treat liver and pancreatic cancer (radio-pharmacy).

Health Hazards

Rhenium is a toxic metal. Exposure to rhenium can lead to irritation of eyes and skin. While, inhalation and ingestion of rhenium can lead to disturbance in respiratory and digestive tract, respectively. The vapors of rhenium cause breathing difficulty and dizziness. Certain compounds of rhenium, such as rhenium trichloride are highly toxic.

Isotopes of Rhenium

There are 25 radioactive isotopes of rhenium. Rhenium has only one stable isotope, rhenium-185. Rhenium-185 is quite rare, as natural rhenium contain about 37.4 % of rhemium-185 and about 62.6% of rhenium-187. Rhenium-187 is not highly unstable as it has a half-life of about 1010  years.

REFERENCES

[1]. “Rhenium: Statistics and Information”. Minerals Information. United States Geological Survey. 2011. Retrieved 2011-05-25

[2]. Emsley, John (2001). “Rhenium”. Nature’s Building Blocks: An A-Z Guide to the Elements. Oxford, England, UK: Oxford University Press. pp. 358–360. ISBN 0-19-850340-7.

[3]. Tessalina, S.; Yudovskaya, M.; Chaplygin, I.; Birck, J.; Capmas, F. (2008). “Sources of unique rhenium enrichment in fumaroles and sulphides at Kudryavy volcano”. Geochimica et Cosmochimica Acta. 72 (3): 889. Bibcode:2008GeCoA..72..889T. doi:10.1016/j.gca.2007.11.015.

[4]. Holleman, Arnold F.; Wiberg, Egon; Wiberg, Nils (1985). “Rhenium”. Lehrbuch der Anorganischen Chemie (in German) (91–100 ed.). Walter de Gruyter. pp. 1118–1123. ISBN 3-11-007511-3.

Radon

Radon is radioactive gas and was discovered by 1899 by Ernest Rutherford and Robert B. Owens. It is formed by the radioactive decay of radium. Radon is the heaviest gas and a known air pollutant.

History and Discovery

Radon was discovered by Ernest Rutherford and Robert B. Owens in 1899.  In the same year Pierre and Marie Curie observed gas emission from radon. And Friedrich Ernst Dom (1900) named the radioactive gas ‘Radium Emanation’ [1]. Ramsay and Robert Whytlaw-Gray found various characteristics of this distinct gas, including density and melting temperature in 1909. They proposed that radon is the heaviest among all known gases.  In early time, Radon was named as niton that was derived from Latin word ‘’nitens’’ meaning “shinning”. The International Union of Pure and Applied Chemistry (IUPAC) named it as Radon in 1923 [2].

Radon

Periodic Table ClassificationGroup 18
Period 6
State at 20CGas
ColorColorless gas
Electron Configuration[Xe] 4f14 5d10 6s2 6p6
Electron Number86
Proton Number86
Electron Shell2, 8, 18, 32, 18, 8
Density9.73 g.cm-3 at 20°C
Atomic number86
Atomic Mass222.00 g.mol -1
Electronegativity according to Pauling2.20

Occurrence

Radon is present in indoor and outdoor areas. It is produced by radioactive decay of radium and thorium. Naturally, radium is present in uranium ores. Uranium is present in small quantity in all soil and rocks. Radon quantity in atmosphere is very low but in houses its concentration is very high. Radon gas can enter in the building through cracks in floor and wall. Its concentration is very high in mining areas, spring waters and hot water. Japan and Germany have radium rich springs that emit high concentrations of radon. Ground water has high concentration of radon due to continuous radioactive decay of radon as compared to the surface water. It is also found in petroleum as radon and propane has the same temperature and pressure curves and is often isolated during the purification of petroleum [3].

Physical Characteristics

Radon is a colorless, odorless and tasteless gas which makes it presence hard to detect by humans. Radon seeps up through the ground and diffuses into air. Radon exhibits brilliant yellow phosphorescence at temperature below its freezing point. The density of radon is significantly high and is nine times higher than air (9.73kg/m3). Radon is about 100 times heavier than hydrogen. Unlike oxygen, radon is a single atom gas which makes it easily penetrate able through various obstacles, including paper, plastic bags, paints, building materials like gypsum board, concrete block and certain insulations. Radon gas liquefies at -61.80C and freezes at-710C.  Radon is springily soluble in water but more soluble in organic solvents. The atomic number of radon is 86 and atomic mass is 222.

Chemical Characteristics

Radon is inert gas and chemically unreactive. Radon is inert to most common chemical reactions including combustion. It is metalloid which means radon lies on the diagonal of the periodic table between the true metals and nonmetals, so it exhibits characteristics of both. In its ionic state it can displace H+, Na+, Cs+, Ca+ and Ba2+ ions. Radon has lower electronegativity than xenon, so it is relatively reactive. The stability of radon hydrate is similar with the hydrates of chlorine or sulfur dioxide but significantly higher than hydrates of hydrogen sulfide. Radon is oxidized by strong oxidizing agent like fluorine and forms radon difluoride.  It is mostly exit in two possible states 0 and +2.

Significance and Uses

  • Radon is commercially for radiation therapy. The radioactivity of radon is molecular damaging is being widely used to kill cancerous cell.
  • In groundwater, the changing concentration of radon is helpful for examination of earthquake prediction.
  • Radon has been used for presumed medical effects in spas.
  • It is useful in geological research for tracking air masses.
  • Radon is needed and delivered in sealed gold needles.
  • It is also used in hydrologic research due to its rapid loss of air.
  • Radon is helpful in exploration of new reserve of petroleum and uranium.

Health Hazards

The primary routes of human exposure to radon is inhalation and ingestion. High concentration of radon in underground water may contribute to radon toxicity [4]. Building materials like granite countertops in a home would increase radiation level. Radon quickly decay and produced radioactive particles which when inhaled damage lungs cells and lead to lung cancer. Leukemia is also caused by radon exposure in adults and children. Radon exposure level is higher for people who are working in uranium processing factories and dealing with phosphate fertilizers. Radon is second leading cause of lung cancer after cigarette smoking.

Isotopes of Radon

Radon has thirty-seven isotopes having atomic masses ranging from 193 to 229. It has no stable isotopes. 222Rn is the stable isotope having a half-life of 3.8 days. It is decay product of 226Rn and 238U. Three isotopes of radon have a half –life of over an hour like 211Rn, 210Rn and 224Rn. 220Rn isotope is product of natural decay of stable thorium.

REFERENCES

[1]. Dorn, F. E. (1900). “Die von radioactiven Substanzen ausgesandte Emanation“(PDF). Abhandlungen der Naturforschenden Gesellschaft zu Halle23: 1–15

[2].https://www.azom.com/article.aspx?ArticleID=7948

[3].“Potential for Elevated Radiation Levels In Propane”(PDF). National Energy Board. April 1994. Retrieved 2009-07-07.

[4]. https://www.cancer.org/cancer/cancer-causes/radiation-exposure/radon.html

Polonium

Polonium is a highly radioactive element. It was discovered in 1989 owing to its highly radioactive nature.

History and Discovery

Polonium was discovered by Marie and Pierre Curie from the ores of uranium in 1989. It was identified as a distinct element due to its highly radioactive nature. Later, in 1902, Willy Marckwald was able to isolate around 3 milligrams of polonium. Commercial production of polonium started during the 2nd World War in US. It was used as the crucial component of the nuclear weapon, Fat Man bomb that was detonated on Nagasaki in 1945 [1]. The name of the element has been derived from the word Polonia, that is Latin for Poland. So, it is basically named after the homeland of its discoverer, the Curies [2].

Polonium

Periodic Table ClassificationGroup 16
Period 6
State at 20CSolid
ColorSilvery
Electron Configuration[Xe] 4f14 5d10 6s2 6p4
Electron Number84
Proton Number84
Electron Shell2, 8, 18, 32, 18, 6
Density9.30 g.cm-3 at 20°C
Atomic number84
Atomic Mass209.00 g.mol -1
Electronegativity according to Pauling2.00

Occurrence

Polonium is a very rare element. It is highly radioactive and has a short half-life, so its natural abundance is very limited and is present in trace amounts. It occurs in uranium ores and is considered as the daughter of uranium-238, as it is formed during the process of radioactive decay of parent element, uranium. In uranium ores, it is present in about 0.1 mg per metric ton. The natural amount of polonium in the Earth crust is not harmful. Polonium is also formed artificially by the neutron irradiation of bismuth, but this process also yields only milligrams of polonium. Polonium has also been reported to be present in smoke of tobacco leaves that are grown in fertilizers containing phosphate. Traces of polonium have been found to be present in sea food.

Physical Characteristics

Polonium is a shiny silver metal. It exists in two allotropic forms, alpha and beta. The alpha form exists in a single atom arranged in a cubic crystal at standard temperature and pressure. While the beta form exists in a complex rhombohedral structure [3]. The atomic number of polonium is 84 and atomic mass is 209.

Chemical Characteristics

Polonium compounds have a wide range of oxidation states: 4, 2, -2. There are very few naturally occurring compounds of polonium. There are around 50 synthetic or artificially made compounds of polonium. Due to its highly reactive nature, it causes radiolysis of chemical bonds and little is known about the chemical characteristics and compounds of polonium.

Significance and Uses

  • Polonium is used as a source of alpha particles by various industries for measuring thickness of coatings.
  • Polonium produce intense alpha particles that generate considerable heat, which is used as source of atomic heat to run radioisotope thermoelectric generators in moon rovers and various satellites.
  • Polonium-beryllium alloys are used as trigger or neutron in initiators of nuclear weapons.
  • Polonium is used for discovering oil wells.
  • Polonium is used a source of static charge in making photographic plates, plastic sheets etc.

Health Hazards

Polonium is a highly toxic element. Its acute radioactivity makes it very dangerous and is considered more toxic than hydrogen cyanide (polonium-210 is about 250,000 times more toxic). The alpha particles produced by polonium can cause severe damage to organic tissues when absorbed, ingested or inhaled. On average, exposure of acute polonium radiation of around 4.5 Sv is considered as the lethal dose (LD50). The biological half-life of polonium-210 is around 50 days and the lethal does of polonium-210 is 0.089 microgram. Theoretically, one 1 gram of polonium-210 can adverse effect 20 million people and half of them will die [4].

Isotopes of Polonium

Polonium have 33 known isotopes. Polonium is highly radioactive, and all its isotopes are highly unstable and radioacitve. The atomic masses of polonium isotopes range in atomic masses from 188 to 220u. Poloium-214, polonium-210 and polonium-218 are produced during the decay chain of uranium-238. Polonium-209 is the most stable isotope and have a half-life of around 125 years [5].

REFERENCES

[1]. Nuclear Weapons FAQ, Section 4.1, Version 2.04: 20 February 1999. Nuclearweaponarchive.org. Retrieved on 2013-04-28.

[2]. Pfützner, M. (1999). “Borders of the Nuclear World – 100 Years After Discovery of Polonium”. Acta Physica Polonica B. 30: 1197. Bibcode:1999AcPPB..30.1197P

[3]. The beta Po (A_i) Structure”. Naval Research Laboratory. 2000-11-20. Archived from the original on 2001-02-04. Retrieved 2009-05-05

[4]. Carey Sublette (2006-12-14). “Polonium Poisoning”. Retrieved 2009-05-05

[5]. Boutin, Chad. “Polonium’s Most Stable Isotope Gets Revised Half-Life Measurement”. nist.gov. NIST Tech Beat. Retrieved 9 September 2014

Platinum

Platinum is a precious and strong metal and has been known since ancient times. It was formally discovered in 1753 in South America.

History and Discovery

Platinum is an ancient metal, as in around 1200 BC, it was identified as a contamination in gold in ancient Egypt. The traces of platinum have been found in pre-Columbia American civilizations, where it was used in making artifacts of white gold. Later, Antonio de Ulloa and Don Jorge Juan (1753) found raw platinum from mines and studied its chemical and physical properties in 1748 and identified it as a distinct metal [1]. In 1752, Henrik Scheffer published a comprehensive description of the novel metal as termed it as “white gold”. The name platinum has been derived from the word platino, which is the Spanish word for little silver [2].

Platinum

Periodic Table ClassificationGroup 10
Period 6
State at 20CSolid
ColorSilvery white
Electron Configuration[Xe] 4f14 5d9 6s1
Electron Number78
Proton Number78
Electron Shell2, 8, 18, 32, 17, 1
Density21.45 g.cm-3 at 20°C
Atomic number78
Atomic Mass195.08 g.mol -1
Electronegativity according to Pauling2.28

Occurrence

Platinum is a rare transition metal. It is present in a concentration of as low as around 0.005 ppm (5micrograms per kg) in the Earth’s crust. Platinum is mostly present in its native form and as alloy with iron. It is primarily prevalent in the alluvial deposit layer along with sand and clay particles. Various ores, including copper and nickel deposits contain platinum in combination with sulfide, arsenide and antimonides. The most common ore of platinum is sperrylite (PtAs2). Cooperite ((Pt,Pd,Ni)S is the sulfide ore of platinum and is present in South Africa, although this ore is quite rare. The largest platinum deposits are present in South Africa, India, Colombia and Russia [3].

Physical Characteristics

Platinum is a silvery white, beautiful metal. It is ductile, lustrous and malleable and is considered the most ductile metal [4]. Platinum is highly stable at high temperature and has a high boiling point (3800 °C). It is very resistant to corrosion. Platinum is a fair conductor of electricity. Platinum is not tarnished in the presence of air or heat. It does not react with acids but is readily dissolved in aqua regia (mixture of concentrated hydrochloric acid and nitric acid). The atomic number of platinum is 78 and its atomic mass is 195.09.

Chemical Characteristics

Platinum is a chemically stable element as it is one of the least reactive metals (Nobel metal). platinum have two oxidation states, +2 and +4. Platinum readily reacts with carbon. Certain non-metals, including phosphorus, silicon and sulfur also combine with platinum. Platinum is readily attacked by peroxides and fluorine at high temperatures. Platinum (IV) also forms oxide, PtO2 (also called Adam’s catalyst).

Significance and Uses

  • Platinum is widely used as a catalyst in exhaust system of internal combustion engine where it is part of the catalytic converter.
  • Platinum is used in making ornaments, artifacts and jewellery.
  • Platinum is used in making dental alloys and implants.
  • Various surgical tools, and laboratory utensils are made of platinum.
  • Platinum is used in making electrical contact points and resistance wires.
  • Platinum is used in aircraft and sport car industries.
  • Platinum is used in making liquid glass display in laptops
  • Platinum is used to make optical fibers.

Health Hazards

Platinum is non-toxic, but certain salts of platinum are considerably dangerous and carcinogenic. Platinum toxicity is primarily an occupational hazard, as it is emitted from cars and vehicles with leaded gasoline. And personals working at garages and terrains of automobile companies are considered be at risk of platinum toxicity. The exposed individual can experience irritation of throat, eyes and nose and continuous exposure can develop skin allergies and respiratory trouble. There are certain health care standards that propose that about 1 mg/m3 over an 8-hour workday is considered as a harmless exposure limit (REL) for individuals exposed to platinum [5].

Isotopes of Platinum

Platinum has 35 isotopes. There are six isotopes in naturally occurring platinum: platinum-190, platinum-192, platinum-194, platinum-195, platinum-196 and platinum-198. The most abundant and the only stable isotope is platinum-195.  

REFERENCES

[1]. Weeks, M. E. (1968). Discovery of the Elements (7th ed.). Journal of Chemical Education. pp. 385–407. ISBN 978-0-8486-8579-9. OCLC 23991202.

[2]. Harper, Douglas. “platinum”. Online Etymology Dictionary.

[3]. Loferski, P. J. (July 2012). “Platinum–Group Metals” (PDF). USGS Mineral Resources Program. Archived (PDF) from the original on 7 July 2012. Retrieved 17 July 2012

[4]. Lagowski, J. J., ed. (2004). Chemistry Foundations and Applications. 3. Thomson Gale. pp. 267–268. ISBN 978-0-02-865724-0.

[5]. “CDC – NIOSH Pocket Guide to Chemical Hazards – Platinum”. www.cdc.gov. Archived from the original on 21 November 2015. Retrieved 21 November 2015.

Osmium

Osmium is a Nobel metal and belongs to the platinum family. It is the densest and corrosion-resistant element. It was discovered in 1803.

History and Discovery

Osmium has an intertwined history with platinum and dates to the late 17th century. Initially, in 1748, platinum was identified as a distinct element and osmium was obtained as an insoluble impurity when platinum was dissolved in aqua regia. Later, in 1803, Smithson Tennant analyzed the insoluble fraction and identified two new elements, iridium and osmium. Osmium was identified due to its unique smell and formation of yellow solution when reacted with sodium hydroxide at high temperature. Osmium was name after the Greek work osme, which refers to smoky and shy smell due to the formation of osmium tetraoxide [1].

Osmium

Periodic Table ClassificationGroup 8
Period 6
State at 20CSolid
ColorSilvery, blue cast
Electron Configuration[Xe] 4f14 5d6 6s2
Electron Number76
Proton Number76
Electron Shell2, 8, 18, 32, 14, 2
Density22.60 g.cm-3 at 20°C
Atomic number76
Atomic Mass190.23 g.mol -1
Electronegativity according to Pauling2.20

Occurrence

Osmium is the one of the rarest natural element [2]. It is present in about 50 parts per trillion in the Earth’s crust. Osmium is present in nature in elemental form or as alloy with iridium. There are two most common alloys of osmium, iridosmium and osmiridium. Osmium is also found in alloys or copper and nickel, but they are quite rare. Currently, osmium is primarily extracted from nickel and platinum ores [3]. The largest natural reserves of osmium have been discovered in South Africa and are also present in Russia.

Physical Characteristics

Osmium is a silver metal with a grayish blue tint. It is very hard and brittle. Osmium belongs to the platinum family. It is considered as the densest metal and have a density of around 22.59 g/cm3 [4]. Osmium retains its lustrous shine even at high temperature and is very resistant to corrosion. Osmium has one of the highest melting and boiling points. It has the lowest vapor pressure among the members of platinum group.

Chemical Characteristics

There are various oxidation states of osmium, ranging from -2 to +8, and the most common are +2, +3 and +8. Osmium tetra-oxide exhibit the oxidation of +8 and is formed by the exposure of powdered osmium to air. This pale-yellow compound has a characteristic smell and is highly toxic. Osmium reacts with base, such as ammonia and forms nitride-osmates. Osmium reacts with halogens, and reacts with fluorine to form osmium pentafluoride, while forms tribromide, triiodide, and diiodide with other halogens.

Significance and Uses

  • Osmium alloys are used in making hard and high-wear items, including instrument pivots, tips of fountain pen, compasses and electrical contacts.
  • Osmium tetroxide is used for the detection of fingerprints.
  • Osmium tetroxide is used in electron microscopy for staining of fatty tissues. It is used in transmission electron microscopy (TEM) for biological studies.
  • Osmium is used in arthritis therapy through a technique termed as synovectomy.

Health Hazards

Osmium in elemental form is non-toxic, however, certain salts and compounds of osmium pose various health hazards. Osmium is powder form undergoes spontaneous inflammation when exposed to air, so care should be taken while its handling. Fumes of osmium tetroxide are very toxic and cause problems if inhaled, ingested or comes in contact with skin. It rapidly absorbs into the tissues and lead to severe irritation and lung congestion [5].

Isotopes of Osmium

Osmium has seven naturally occurring isotopes. There are six stable isotopes of osmium, osmium-184, osmium-187, osmium-188, osmium-189, osmium-190 and osmium-192. The most abundant stable isotope is osmium-192. The radioactive isotope of osmium is osmium-186 and has a very long half-life (2 × 1015 years).

REFERENCES

[1]. Weeks, M. E. (1968). Discovery of the Elements (7 ed.). Journal of Chemical Education. pp. 414–418. ISBN 978-0-8486-8579-9. OCLC 23991202.

[2]. “Reading: Abundance of Elements in Earth’s Crust | Geology”. courses.lumenlearning.com. Retrieved 2018-05-10

[3]. George, Micheal W. “2006 Minerals Yearbook: Platinum-Group Metals” (PDF). United States Geological Survey USGS. Retrieved 2008-09-16

[4]. Arblaster, J. W. (1995). “Osmium, the Densest Metal Known”. Platinum Metals Review. 39 (4): 164

[5]. George, Micheal W. “2006 Minerals Yearbook: Platinum-Group Metals” (PDF). United States Geological Survey USGS. Retrieved 2008-09-16

Lead

Lead has been known since old ages and its use has been largely limited due to its high toxicity. It is the heaviest stable element and is resistant to corrosion.

History and Discovery

Lead is a prehistoric metal and was used by people of ancient Rome and Western Asia around 7000 BCE. It was widely used to make water pipes by the Romans and named it as plumbum nigrum (black lead). The use of lead decreased with the fall of the Roman Umpire. Lead was used as a currency in Ancient Chinese courts. Civilizations of Indus valley and Ancient Greece used lead to make amulets, glasses, ornaments, glazes and sinkers in fishing net. The name plumbum, was given to the metal and the English word plumbing was originated from this Latin word. The origin of name of lead is intertwined with tin, as olovo translates to lead in Czech, while it translate to tin in Russian language. The word lead has been derived from Old English word lead.

Lead

Periodic Table ClassificationGroup 14
Period 6
State at 20CSolid
ColorMetallic gray
Electron Configuration[Xe] 4f14 5d10 6s2 6p2
Electron Number82
Proton Number82
Electron Shell2, 8, 18, 32, 18, 4
Density11.35 g.cm-3 at 20°C
Atomic number82
Atomic Mass207.20 g.mol -1
Electronegativity according to Pauling1.87 (+2)

Occurrence

Lead is an abundant metal and is present around 14 ppm in the Earth’s crust. It is considered as the 38th most abundant element on Earth [1]. It is primarily present in combined form with sulfur and is rarely found in elemental or metallic form. The most common mineral of lead is galena (PbS). It is found in zinc ores. There are various impurities in lead minerals and ores, including tin, arsenic, gold, silver and copper. The largest deposits of lead are found in Australia, Russia, China, US, and Ireland [2].

Physical Characteristics

Lead is a silver colored metal with a tint of blue. It tarnishes to dark gray color when exposed to air. Lead is soft but is significantly denser than other metals. it is malleable and has a low melting point. Lead has the atomic number of 82, which is considered as the highest among all stable naturally occurring elements.

Chemical Characteristics

Lead is not very reactive. It belongs to the post-transition metal group in the periodic table. Lead frequently form stable covalent bonds as compared ionic bonding. Lead reacts with acids and bases. The common oxidation state of lead in compounds is +2. Lead can also form bonds with other lead molecule and can acquire unique arrangement, such as rings, chain and polyhedral structures.

Significance and Uses

  • Lead toxicity has led to major decline in its uses since mid-1980s. It is still used in various industries where its toxic effects are minimal for the environment and humans.
  • Lead has been widely used for bullets.
  • It is used in weight belts used by scuba divers to counteract their buoyancy.
  • Lead is used to cover underwater cables as it is resistant to corrosion.
  • It is widely used in construction industry. And is part of gutters, roofing material, cladding etc., to reinforce the structure.
  • Lead is used to make sculptures and statues.
  • Lead alloys with copper, including bronze and brass are used to make components of machinery.
  • Lead is used in lead batteries and various supercapacitors are being used to in US, Australia and Japan in various megawatt scale applications.
  • Lead is used to detect aldehydes, and organic acids (Oddy test).

Health Hazards

Lead is highly toxic element. Its toxicity was recognized in the late 19th century. It can accumulate in bones and soft tissues and damages the neurons and nervous system. Lead has the ability to cross the blood-brain barrier and cause damage to brain and other organs. Lead toxicity is specially alarming for children as it can lead to lifelong neurological disorders, and behavioral challenges. Lead exposure during pregnancy can cause miscarriage and can lead to delay in puberty in girls. Lead is known to interfere with many biologically significant enzymes, including enzyme of heme synthesis pathway [3]. Lead toxicity is primarily caused by the ingestion of lead-based paints, in toys, or in home. Lead dust from furniture or window sill painted with lead can enter the body via hand to mouth contact. Inhalation of lead is the second most common pathway of lead toxicity, and lead from automobiles and cigarette smoking can cause severe toxic effects on the human body. About 100 mg/m3 of airborne lead concentration is considered dangerous to health and life [4]. Lead can persist in our environment, especially organic soil and can remain there for hundreds of years. From contaminate soil and water, lead can enter the food chain and effect animals. It also enters the human body through consumption of contaminated fruits, and vegetables. Lead can accumulate in bodies of marine animals, especially fishes and cause bioaccumulation.

Isotopes of Lead

Lead consist of four stable isotopes, lead-204, lead-206, lead-207 and lead-208 [5]. There are five unstable isotopes of lead. The atomic number of lead is 83, which makes lead the heaviest stable element and isotope-208 is the heaviest stable nucleus. The theoretical half-life of isotopes of lead is around 1035 to 10189. There are around 43 artificial isotopes of lead, and their atomic mass range from 178-220.

REFERENCES

[1]. Elemental abundance figures are estimates and their details may vary from source to source

[2]. United States Geological Survey 2017, p. 97.

[3]. Cohen, Trotzky & Pincus 1981, pp. 904–06.

[4]. National Institute for Occupational Safety and Health.

[5]. IAEA – Nuclear Data Section 2017

Iridium

Iridium belongs to the platinum group of metals and is highly dense and resistant to corrosion. It was discovered in 1803.

History and Discovery

Ancient South Americans and Ethiopians have used platinum along with iridium. Iridium was discovered as an impurity in platinum metal by Smithson Tennant in 1803. When platinum was dissolved in aqua regia, iridium appeared as dark insoluble residue, which was later identified as a new metal. The name iridium was given by Tennant after the Greek goddess Iris (Goddess of rainbow), as the newly discovered metal formed varying color compounds and salts [1].

Iridium

Periodic Table ClassificationGroup 9
Period 6
State at 20CSolid
ColorSilvery white
Electron Configuration[Xe] 4f14 5d7 6s2
Electron Number77
Proton Number77
Electron Shell2, 8, 18, 32, 15, 2
Density22.4 g.cm-3 at 20°C
Atomic number77
Atomic Mass192.22 g.mol -1
Electronegativity according to Pauling2.20

Occurrence

Iridium is an extremely rare element. And is present in about 0.001 ppm in crustal rocks. Iridium is an element of space and is more abundant on meteorites than in Earth’s crust and has an average abundance of 0.5 ppm [2]. Traces of iridium from core samples of Pacific Ocean and Cretaceous-Paleogene boundary support the hypothesis that massive meteorites showers led to extinction of dinosaurs around 66 million years ago. Due to its low reactivity, iridium is found in its elemental form or in the form of natural alloys, including iridium-osmium alloys (idrosmine and osmiridium). Some minerals of iridium have also been found, but they are quite rare, such as cuproiridsite and irarsite. The annual production and consumption of iridium is only three tons.

Physical Characteristics

Iridium is a whitish silver transition metal. It is brittle solid at standard temperature and pressure. It is a significantly dense metal and is considered as the 2nd densest element (22.56 g/cm3). Iridium is considered as the most corrosion-resistant metal and does not react with water or oxygen even at high temperatures [3]. In powdered form, iridium is highly flammable. Indium has very high boiling and melting points. It can become a super conductor at temperature lower than 0.14K [?]. Indium has an extraordinary ability to withstand deformation and is very stiff. Indium is resistant to most acids and alkalis. It is a very costly metal.

Chemical Characteristics

Iridium is considered as a Nobel metal due to its low reactivity. It does not react with molten metals, acids or silicate. However, certain salts, including potassium and sodium cyanide can react with iridium at high temperature. Iridium also reacts with fluorine at high temperature [4].

Significance and Uses

  • Iridium is widely used in electronic industry and is primarily used as a coating agent.
  • Iridium is used as a catalyst in various chemical industries, such as Cativa process that involves the formation of acetic acid from methanol by carbonylation.
  • Alloys of osmium-iridium are used to make compass bearings, tips of fountain pen and balances used for precision.
  • Iridium alloys are used to make electrical contact points in spark plugs.
  • Iridium is used to make aircraft engines due to its high resistant to corrosion and heat.
  • Iridium radioactive isotope, iridium-192 is used in making energy generators.

Health Hazards

Indium is a highly flammable metal. However, it is not considered very toxic. Exposure to indium can lead to minor irritation of eyes and ingestion can lead to slight stomach disorder.

Isotopes of Iridium

Iridium has only two naturally occurring isotopes, iridium-191 and iridium-193 [5]. And has around 34 artificially occurring isotopes, that range in mass number from 164 to 199. The most stable radioactive artificial isotope is irdium-192 (73 days).

REFERENCES

[1]. Weeks, M. E. (1968). Discovery of the Elements (7th ed.). Journal of Chemical Education. pp. 414–418. ISBN 0-8486-8579-2. OCLC 23991202.

[2]. Iridium” (PDF). Human Health Fact Sheet. Argonne National Laboratory. 2005. Archived from the original (PDF) on March 4, 2012. Retrieved 2008-09-20.

[3]. Emsley, J. (2003). “Iridium”. Nature’s Building Blocks: An A–Z Guide to the Elements. Oxford, England, UK: Oxford University Press. pp. 201–204. ISBN 0-19-850340-7.

[4]. Lagowski, J. J., ed. (2004). Chemistry Foundations and Applications. 2. Thomson Gale. pp. 250–251. ISBN 0028657233.

[5]. Audi, G.; Bersillon, O.; Blachot, J.; Wapstra, A. H. (2003). “The NUBASE Evaluation of Nuclear and Decay Properties”. Nuclear Physics A. Atomic Mass Data Center. 729: 3–128. Bibcode:2003NuPhA.729….3A. doi:10.1016/j.nuclphysa.2003.11.001

Hafnium

Hafnium was discovered in 1923 as a novel metal by Hevesy and Coster. In nature, it exists in combination with zirconium and its alloys have high refractory properties.

History and Discovery

Hafnium was discovered as a novel element by Georg von Hevesy and Dirk Coster in 1923. They analyzed the mineral zircon through X-ray spectroscopic analysis and found the novel element Hafnium. However, its presence was predicted by Dmitri Mendeleev (1869).  The name hafnium has been derived from Latin word Hafnia, that was the name of Copenhagen, the home town of Niels Bohr and the discoverers of hafnium. Bohr’s theory predicted that a novel element was associated with zirconium [1].

Hafnium

Periodic Table ClassificationGroup 4
Period 6
State at 20CSolid
ColorSteel gray
Electron Configuration[Xe] 4f14 5d2 6s2
Electron Number72
Proton Number72
Electron Shell2, 8, 18, 32, 10, 2
Density13.31 g.cm-3 at 20°C
Atomic number72
Atomic Mass178.49 g.mol -1
Electronegativity according to Pauling1.3

Occurrence

Hafnium is not very abundant element and is found in a concentration of about 5.8 ppm in the Earth’s crust. Hafnium does not exist in free metallic form in nature. It is found in combined mineral with zirconium, including thortveitite, alvite [(Hf, Th, Zr) SiO4 H2O] and zircon (ZrSiO4). Hafnium is obtained as byproduct during the refinement of zirconium. However, the separation of hafnium and zirconium is extremely difficult as the two elements closely resemble reach other. Large mineral deposits of hafnium and zirconium have been found in Malawi and Brazil and Australia [2].

Physical Characteristics

Hafnium is a greyish-silver lustrous metal.  It is a transition metal and resembles zirconium in its chemical properties, as both have equal number of valence electrons. It is ductile and is resistant to corrosion. Hafnium is denser than zirconium.

Chemical Characteristics

Hafnium is resistant to attacks by concentrated alkalis. It reacts with halogens to form hafnium tetrahalides. When exposed to air, hafnium forms a protective layer on its surface that is prves to be protective against corrosion. Hafnium also react with carbon, oxygen, sulfur and nitrogen, at elevated temperatures. Hafnium nitride is characterized as the most refractory of all nitrides of metals, and it has melting point of as high as 3310°C. So, it can withstand high temperatures. It has significant nuclear properties as it can absorb high thermal neutrons, whereas, zirconium is transparent to neutrons. The common oxidation state of hafnium is +4. Compounds of hafnium and zirconium have similar attributes.

Significance and Uses

  • Hafnium is widely used to make neutron absorbing rods (control rods) in nuclear reactors.
  • Hafnium is used in incandescent lamps, as it can scavenge nitrogen and oxygen.
  • Hafnium dioxide is being considered as an ideal candidate for use as insulators in High-K gates used in integrated circuits.
  • Hafnium nuclear isomer, Hf-178-ms has potential for use in nuclear energy generation projects and nuclear war heads.
  • Hafnium is used to make electrodes and filaments.
  • Hafnium is used to make various superalloys, with tungsten, niobium and titanium that are used in various significant applications.
  • Hafnium and its carbides are widely used as construction materials that are exposed to very high temperature.
  • Hafnium alloys are used in making simulation of supercomputer that can withstand temperatures as high as 4400 K [3].

Health Hazards

Hafnium metal is non-toxic. However, exposure of various compounds and salts of hafnium are considered potentially dangerous. Hafnium in powdered or fine divided form is considered hazardous and needs to be handled with care. As powdered hafnium can spontaneously ignite when exposed to air (pyrophoric).

Isotopes of Hafnium

Hafnium has 34 isotopes, with mass number ranging from 153 to 186 [3]. There are five stable isotopes of hafnium, hafnium-176 to 180. The most stable radioactive isotope is hafnium-174, that has a half-life of 1015 years [4].

REFERENCES

[1]. Bob Weintraub, George De Hevesy (1885 1966) (pdf document)

[2]. Dubbo Zirconia Project Fact Sheet” (PDF). Alkane Resources Limited. June 2007. Archived from the original (PDF) on 2008-02-28. Retrieved 2008-09-10.

[3]. Georges, Audi; Bersillon, O.; Blachot, J.; Wapstra, A. H. (2003). “The NUBASE Evaluation of Nuclear and Decay Properties”. Nuclear Physics A. Atomic Mass Data Center. 729: 3–128. Bibcode:2003NuPhA.729….3A. doi:10.1016/j.nuclphysa.2003.11.001.

[4]. EnvironmentalChemistry.com. “Hafnium Nuclides / Isotopes”. Periodic Table of Elements. J.K. Barbalace. Retrieved 2008-09-10.

Francium

Francium was discovered in 1939. It is very unstable alkali metal and considered the second rarest element in the earth crust.

History and Discovery

Francium was discovered by Marguerite Perey in 1939, who was studying the decay of actinium-227 by negative beta decay to an isotope of thorium and by alpha emission into an isotope of Francium-223, which was known as actinium.  Dmitri Mendeleev predicted the existence of element based on the gap in the periodic table in 1870. Perey suggested the name francium after France and this name was adopted by the IUPAC (International Union of Pure and Applied Chemistry) in 1949. Francium is the last natural element to be discovered [1].

Francium

Periodic Table ClassificationGroup 1
Period 7
State at 20CSolid (predicted)
ColorSilver-gray-metallic (presumed)
Electron Configuration[Rn] 7s1
Electron Number87
Proton Number87
Electron Shell2, 8, 18, 32, 18, 8, 1
Density0.00 g.cm-3 at 20°C
Atomic number87
Atomic Mass223 g.mol -1
Electronegativity according to Pauling>0.79

Occurrence

Francium is formed by radioactive decay of actinium, and artificially made by bombarding thorium with protons. It is naturally present in uranium and consider the second rarest element in the earth crust. It exists in short-lived radioactive forms and cannot be isolated in pure stable form. It is estimated that less than 30 grams of francium occur at any time in the earth crust.

Physical Characteristics

Francium is the shiny metal in its pure state and exist in liquid form at room temperature rather than a solid. Francium belongs to alkali group of the periodic table so its physical properties are similar with alkali group elements. Its melting point is about 27oC and its boiling point is 677oC, but both have uncertainty due to high radioactivity and is extremely rare in nature. Francium is heaviest known metal of alkali group. Its atomic number is 87 and atomic mass is 223 [2].

Chemical Characteristics

Francium chemical properties are similar with caesium. It has slightly higher ionization energy and electron affinity than caesium. It is the least electronegative element so it is chemically reactive alkali metal. And readily loses it outer shell to become Nobel element. Like alkali metals it is readily oxidized in air and vigorously react with water. It exit in +1 oxidation state. It has slightly higher ionization energy than cesium. Nearly all francium salts are water soluble.

Significance and Uses

  • There are no commercial applications due to its instability and rarity in nature.
  • Francium has been used in research purpose only [3].

Health Hazards

Francium has no known biological role in human life. Its toxicity is just due to its radioactivity, that can cause damage to cells and nuclear material.

Isotopes of Francium

The longest-lived isotope of francium is Fr-223, which has a half-life of only 22 minutes. Thirty four artificial isotopes with atomic masses from 199 to 232 because natural isotope of francium cannot be concentrated. All isotopes decay into astatine, radium or radon.

REFERENCES

[1]. https://www.britannica.com/science/francium

[2]. http://www.newworldencyclopedia.org/entry/Francium

[3]. Winter, Mark. “Uses”. Francium. The University of Sheffield. Retrieved March 25, 2007.

Cesium

Cesium was discovered in 1860. It is outstanding in keeping time with precision, so it is used in atomic clocks. It forms alloys with alkali metals, gold and mercury.

History and Discovery

Cesium is considered the first element who was discovered spectroscopically in 1860 by Robert Bunsen and Gustav Kirchhoff. They also derived its name from Latin caesius ‘’sky-blue’’ due to the formation of unique blue lines in the emission spectrum. [1]

Cesium

Periodic Table ClassificationGroup 1
Period 6
State at 20CSolid
ColorPale gold
Electron Configuration[Xe] 6s1
Electron Number55
Proton Number55
Electron Shell2, 8, 18, 18, 8, 1
Density1.87 g.cm-3 at 20°C
Atomic number55
Atomic Mass132.91 g.mol -1
Electronegativity according to Pauling0.79

Occurrence

Cesium occurs in minute quantity in earth crust in the form of minerals like pollucite (zeolite mineral cesium ore). It is mostly present with rubidium in nature and other alkali metals. The abundance of cesium on the earth crust is about 3 part per million and it is the 50th most common element in the earth crust [2].

Physical Characteristics

Cesium is a silvery-gold metallic element. It is an extremely soft metal. Cesium is one of four elements who exist in liquid form at or near room temperature. In periodic table it belongs to alkaline elements. Its physical properties are similar with rubidium and potassium. In the presence of mineral oil it loses its metallic luster. It has the melting point of 28.5oC and also has a low boiling point 641oC. Its golden color is due to decreasing frequency of light that is why it partially absorbs violet light while other colors are reflected hence it appears yellowish or golden in color. Cesium atomic number is 55 and its atomic mass is 132.90 g/mol.

Chemical Characteristics

Cesium is very reactive and pyrophoric (ignites spontaneously in air). It reacts with water vigorously and explosively, even at low temperatures. Cesium resembles rubidium in its chemical characteristics [3]. Cesium can be handled only under an inert gas, such as argon. It is exit in +1 oxidation state. In compounds it is present as Cs+ and binds ionically with anions. Its salts are usually colorless unless anion itself is colored. Double salts are less soluble but others like phosphate, acetate, carbonate are water soluble. Salts are hygroscopic in nature (attracting and holding water from surrounding). It is difficult to handle cesium because it reacts spontaneously and react with air. Cesium burns readily to form superoxide. Cesium hydroxides is a strong base which can attack glass. It react with halogens and forms fluoride, chloride, bromide and iodide.

Significance and Uses

  • Cesium is used in vacuum tubes as a “getter” to clean the traces of oxygen and other gases when sealed.
  • Cesium compounds with chlorides are used in photoelectric cells.
  • Cesium is used in industries as a catalyst promoter.
  • Cesium nitrate is used to make optical glasses.
  • Cesium is widely used in the production of electricity, electronics and in chemistry.
  • Cesium is also used in the manufacturing of infrared lamps.
  • Cesium is widely used in clocks. And it also used to determine the fundamental unit of time.
  • Cesium salts are used in water treatment and making mineral water.
  • Cesium vapor is used in making magnetometers.
  • Cesium is used in molecular biology for density gradient ultracentrifugation.
  • It is used in the catalytic conversion of sulfur dioxide into sulfur trioxide.
  • Cesiums-137 is radioactive isotope used as a gamma –emitter in various industrial application. It is used in medical field to treat various types of cancer.
  • Cesium and rubidium are used as a carbonate to manufacture high quality glass because they reduce electrical conductivity and improve stability.
  • It is used as cesium formate (anion derived from formic acid) for drilling fluids.

Health Hazards

Due to its high reactivity, cesium is considered as a hazardous metal. People who work in nuclear power station may be exposed to cesium, otherwise there is no health risk associated with cesium. People can experience cell damage due to its radiation effects and may suffer from nausea, vomiting, diarrhea and bleeding.

Isotopes of Cesium

It has thirty-nine known isotopes, having atomic masses ranging from 112 to 151. The only stable isotope of cesium is 133 Cs. Cs-135 has very long half-life of about 2.3 million years.

REFERENCES

[1]. https://www.britannica.com/science/cesium

[2]. Turekian, K. K.; Wedepohl, K. H. (1961). “Distribution of the elements in some major units of the Earth’s crust”. Geological Society of America Bulletin72(2): 175–192.

[3]. Greenwood, N. N.; Earnshaw, A. (1984). Chemistry of the Elements. Oxford, UK: Pergamon Press. ISBN 978-0-08-022057-4.