These mole fractions lead to a value of about 7.00 for the atomic weight of the lithium sample that is depleted in 6Li.įigure 1: Lithium cellproposed for IUPAC’s Periodic Table of the Isotopes.Īt this point, let it be noted that the isotopic abundance values are also weighting factors that relate the thermal neutron absorption cross section (or probability that a neutron reaction will occur) of each stable isotope to the thermal neutron absorption cross section of the natural chemical element. For the isotopically fractionated lithium samples with depleted 6Li in our story, the mole fractions in the extreme case 2 would be 6Li is 0.02007 (or isotopic abundance of 2.007%) and 7Li is 0.97993 (or isotopic abundance of 97.993%). The product of each isotope’s atomic mass and its isotopic abundance, summed over both isotopes leads to a calculated value of 6.94 for the atomic weight of lithium. The standard isotopic reference material for lithium, 1 IRMM-016, has a measured stable isotope ratio that leads to a mole fraction for 6Li of 0.0759 (which corresponds to an isotopic abundance value of 7.59%) and a mole fraction for 7Li of 0.9241 (which corresponds to the isotopic abundance value of 92.41%). Lithium is an element with only two stable isotopes, 6Li and 7Li, and so there is only one stable isotope ratio involved (see Figure 1). This background story brings to light an interesting page of history. Lithium has become the least accurately known atomic weight because of the existence and the distribution in the distant past of some chemical reagents, which were depleted in the 6Li isotope of natural lithium. As a result, the standard atomic weight of lithium is more accurately characterized as a range of atomic weight values from 6.9387 to 6.9959. Li (lithium) is one of a handful of elements whose stable isotopic ratio varies in natural terrestrial samples to the extent that the resulting atomic weight variation exceeds the measurement uncertainty on the value. Lithium reacts with water, but not as violently as sodium.Įstimated Crustal Abundance: 2.0×10 1 milligrams per kilogramĮstimated Oceanic Abundance: 1.The Impact of Depleted 6Li on the Standard Atomic Weight of Lithium Lithium carbonate (Li 2CO 3) is used as a drug to treat manic depression disorder. Lithium stearate (LiC 18H 35O 2) is used as a general purpose and high temperature lubricant. Lithium hydroxide (LiOH) is used to remove carbon dioxide from the atmosphere of spacecraft. Lithium is the lightest known metal and can be alloyed with aluminium, copper, manganese, and cadmium to make strong, lightweight metals for aircraft. It is used to make special glasses and ceramics, including the Mount Palomar telescope's 200 inch mirror. Lithium has the highest specific heat of any solid element and is used in heat transfer applications. Many uses have been found for lithium and its compounds. Lithium is not found free in nature and makes up only 0.0007% of the earth's crust. Today, larger amounts of the metal are obtained through the electrolysis of lithium chloride (LiCl). It was first isolated by William Thomas Brande and Sir Humphrey Davy through the electrolysis of lithium oxide (Li 2O). Lithium was discovered in the mineral petalite (LiAl(Si 2O 5) 2) by Johann August Arfvedson in 1817.
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