註釋 The present volume continues the edition of a number of supplement volumes dealing with the elements tungsten and molybdenum. The compounds of molybdenum with noble gases, hydrogen and oxygen, anhydrous antimony-, bismuth- and alkalimolybdates as well as compounds of molybdenum oxides with oxides of other metals have been described in volume B 1 and B 2. The oxide hydrates and the molybdate ions are dealt with in volume B 3a. The volume molybdenum supplement B 4 contains the hydrous oxocompounds of the metals Sb to Cr with molybdenum. Description of the element molybdenum is covered by the supplement volumes A 1, A 2a, A 2b and A3. In the first part of this volume the description of the oxomolybdenum (VI) species in aqueous solution, which was started in the "Molybdenum" Supplement Volume B 3a, 1987, is continued and completed with the Section on the chemical reactions. After a general overview on the chemical properties of the molybdate ions in aqueous solution, the typical reactions are treated in separate chapters, e.g., reduction, precipitation, formation of heteropolymolybdate ions, reactions with organic ligands, etc. The second part of this volume deals with the oxomolybdenum (VI) species in nonaqueous (organic) solvents. Most of the polymeric species are different from those occurring in aqueous media. The last Section on the oxospecies in solution describes the species in melts such as alkali chlorides, nitrates, and chromates. Finally, the peroxomolybdate ions are treated in a separate Section. 