Tellurium

This week's element is tellurium, which has the symbol Te and the atomic number, 52. Its name comes from the Latin, tellus , for "earth". Despite its name, this lustrous, pale grey metalloid is quite rare on earth, rarer than it is elsewhere in the universe, in fact. The reason for its comparative rarity is attributed to the formation of H 2 Te, a volatile gas that was lost to space during the early formation of earth. Tellurium is used in a number of industrial and commercial applications. It is alloyed with stainless steel and copper to improve their machinability and tellurium is used as a semiconductor, cadmium telluride is used in solar panels because it has the highest efficiency for electricity generation, tellurium speeds the curing of rubber and renders it less susceptible to aging and to the softening effects of oil, and tellurium oxide , Te O , is used in some rewritable CDs and DVDs. When I was a microbiologist, one of the many types of growth media that I used to diagnose human pathogens was an agar made with serum and potassium tellurite ( K 2 Te O 3 ). This agar is used specifically to diagnose the human respiratory pathogen, Corynebacterium diphtheriae . Tellurite agar is a selective medium because tellurium inhibits growth of a variety of bacteria, and it is a differential medium because Corynebacterium will reduce tellurite to metallic tellurium, producing characteristic black or brownish-black colonies on the otherwise pale straw-coloured and transparent agar. In humans and other animals, tellurium has no known biological role, but the body does metabolise it to create the volatile gaseous compound, dimethyl telluride, ( C H 3 ) 2 Te, which is excreted in sweat and exhaled, and is the source of a charmingly potent "garlic breath", similar to what happens with selenium ingestion. (Which makes me wonder why don't any of these elements make people smell minty or fruity? Why must we always smell like a litter box?) I should point out that taking vitamin C can reduce these odoriferous effects. Tellurium can be toxic if ingested in high enough quantities. * Chemically speaking, the discovery of tellurium caused the inventor of the periodic table of elements, Dmitri Mendeleev, a lot of headaches. This is because tellurium has an atomic mass of 127.6 whilst the element that comes after it, iodine, is lighter with an atomic weight of 126.9. Mendeleev concluded that the atomic mass for one of these two elements must be wrong because tellurium clearly preceded iodine in the periodic table. After 50 years of headbanging frustration and effort by a number of chemists to accurately determine the atomic mass of these two elements, the concept of chemical isotopes was discovered. Isotopes are variant forms of an element that maintain the element's characteristic number of protons, but contain variable numbers of neutrons. As it turns out, the most common isotopes of tellurium have atomic masses of 128 and 130, whilst iodine's most common isotope has an atomic mass of 127. Thus, tellurium has an average atomic mass of 127.6 whilst iodine has an average atomic mass of 126.9. Here's our favourite chemistry professor telling us more about tellurium: Visit PeriodicVideos 's YouTube channel [ video link ]. * [added 1430 on 2 March 2012] Tellurium is "[h]ighly toxic, may be fatal if inhaled, swallowed or absorbed through skin. Avoid any skin contact. Effects of contact or inhalation may be delayed." [ link ]. Sodium tellurite is also toxic: "The material is both an oral and dermal toxic hazard. The material is toxic by ingestion. Oral ingestion of tellurium compounds is generally regarded as extremely toxic. The probable oral lethal dose is 5-50 mg/kg or between 7 drops and 1 teaspoonful for a 70 kg (150 pound) person. Tellurium compounds are regarded as super toxic for skin exposures." [ link ]. .. .. .. .. .. .. .. .. .. .. .. .. Video journalist Brady Haran is the man with the camera and the University of Nottingham is the place with the chemists. You can follow Brady on twitter @ periodicvideos and the University of Nottingham on twitter @ UniNottingham You've already met these elements: Antimony : Sb , atomic number 51 Tin : Sn , atomic number 50 Indium : In , atomic number 49 Cadmium : Cd , atomic number 48 Silver : Ag , atomic number 47 Palladium : Pd , atomic number 46 Rhodium : Rh , atomic number 45 Ruthenium : Ru , atomic number 44 Technetium : Tc , atomic number 43 Molybdenum : Mo , atomic number 42 Niobium : Ni , atomic number 41 Zirconium : Zr , atomic number 40 Yttrium : Y , atomic number 39 Strontium : Sr , atomic number 38 Rubidium : Rr , atomic number 37 Krypton : Kr , atomic number 36 Bromine : Br , atomic number 35 Selenium : Se , atomic number 34 Arsenic : As , atomic number 33 Germanium : Ge , atomic number 32 Gallium : Ga , atomic number 31 Zinc : Zn , atomic number 30 Copper : Cu , atomic number 29 Nickel : Ni , atomic number 28 Cobalt : Co , atomic number 27 Iron : Fe , atomic number 26 Manganese : Mn , atomic number 25 Chromium : Cr , atomic number 24 Vanadium : V , atomic number 23 Titanium : Ti , atomic number 22 Scandium : Sc , atomic number 21 Calcium : Ca , atomic number 20 Potassium : K , atomic number 19 Argon : Ar , atomic number 18 Chlorine : Cl , atomic number 17 Sulfur : S , atomic number 16 Phosphorus : P , atomic number 15 Silicon : Si , atomic number 14 Aluminium : Al , atomic number 13 Magnesium : Mg , atomic number 12 Sodium : Na , atomic number 11 Neon : Ne , atomic number 10 Fluorine : F , atomic number 9 Oxygen : O , atomic number 8 Nitrogen : N , atomic number 7 Carbon : C , atomic number 6 Boron : B , atomic number 5 Beryllium : Be , atomic number 4 Lithium : Li , atomic number 3 Helium : He , atomic number 2 Hydrogen : H , atomic number 1 Here's a wonderful interactive Periodic Table of the Elements that is just really really fun to play with! .. .. .. .. .. .. .. .. .. .. .. .. twitter: @ GrrlScientist facebook: grrlscientist evil google+: grrlscientist email: [email protected]