Geological specimens are known in which the element has an isotopic composition outside the limits for normal material. The difference between the atomic weight of the element in such specimens and that given in the Table may exceed the stated uncertainty.
Range in isotopic composition of normal terrestrial material prevents a more precise value being given; the tabulated value should be applicable to any normal material.
Modified isotopic compositions may be found in commercially available material because it has been subject to an undisclosed or inadvertent isotopic fractionation. Substantial deviations in atomic weight of the element from that given in the Table can occur.
Commercially available Li materials have atomic weights that range between 6.939 and 6.996; if a more accurate value is required, it must be determined for the specific material [range quoted for 1995 table 6.94 and 6.99].
Element has no stable nuclides. The value enclosed in brackets, e.g. [209], indicates the mass number of the longest-lived isotope of the element. However three such elements (Th, Pa, and U) do have a characteristic terrestrial isotopic composition, and for these an atomic weight is tabulated.
The names and symbols for elements 112-118 are under review. The temporary system recommended by J Chatt, Pure Appl. Chem., 51, 381-384 (1979) is used above. The names of elements 101-109 were agreed in 1997 (See Pure Appl. Chem., 1997, 69, 2471-2473) and for element 110 in 2003 (see Pure Appl. Chem., 2003, 75, 1613-1615). The approved name for element 111 is also included.
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