Dwi-

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In chemistry, the prefix dwi- (Sanskrit: "two") was formerly used to name undiscovered chemical elements lying two periods under a known element in the periodic table. For example, rhenium was called dwi-manganese before its discovery in 1926. Current official IUPAC practice is to use a systematic element name based on the atomic number of the element as the provisional name, instead of being based on its position in the periodic table as these prefixes require.

[edit] See also

• Mendeleev's predicted elements