Conversion Charts

• Unit of Measure Conversion Factor
• Temperature Conversion Formula
• Weight Conversion Table
• Volume Conversion Table
• Length Conversion Table
• Flow Rate Conversion Table
• Common Molecular Biology Conversion Factors
• Acid Base Concentrations

Atomic Weights

The atomic weights of many elements are not invariant but depend on the origin and treatment of the material. The footnotes to this table elaborate the types of variation to be expected for individual elements. The values of Ar(E) given here apply to elements as they exist naturally on earth and to certain artificial elements. When used with due regard to the footnotes they are considered reliable to ±1 in the last digit, unless otherwise stated. Values in parentheses are used for radioactive elements whose atomic weights cannot be quoted precisely without knowledge of the origin of the elements; the value given is the atomic mass number of the isotope of that element of longest known half-life.

Pure & Applied Chemistry 63, pp. 975–990 (1991); Pure & Applied Chemistry 64, pp. 1519–1534 (1992); Chemistry International 16, p. 68 (1994).

Atomic Weights of the Elements, 1991— Scaled to the relative atomic mass, Ar(12C) = 12

• Element for which the value of Ar is that of the radioisotope of longest half-life. .
• Element for which range in isotopic composition of normal terrestrial material prevents a more precise Ar(E) being given; the listed value should be applicable to any normal material. .
• Element for which geologically exceptional 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 considerably the implied uncertainty. .
• Element for which modified isotopic compositions may be found in commercially available material because it has been subjected to an undisclosed or inadvertent isotopic separation. Substantial deviations in atomic weight of the element from that given in the table can occur.