Polonium selenate

P0O2 is obtained by direct combination of the elements at 250° or by thermal decomposition of polonium(IV) hydroxide, nitrate, sulfate or selenate. The yellow (low-temperature) fee form has a fluorite lattice it becomes brown when heated and can be sublimed in a stream of O2 at 885°. However, under reduced pressure it decomposes into the elements at almost 500°. There is also a high-temperature, red, tetragonal form. P0O2 is amphoteric, though appreciably more basic than Te02 e.g. it forms the disulfate Po(S04)2 for which no Te analogue is known. 

The physical properties of the metal (Table II) resemble those of thallium, lead and bismuth, its neighbors in the Periodic Table, rather than those of tellurium, its lower homologue. The low melting and boiling points are particularly noteworthy an attempted study of the Hall effect in polonium metal has also been reported (90). In chemical properties the metal is very similar to tellurium, the most striking resemblance being in its reactions with concentrated sulfuric acid (or sulfur trioxide) and with concentrated selenic acid. The products are the bright red solids, PoSOs and... 

Aqueous 1 M chromium trioxide (12) does not react with metallic polonium, but with polonium(IV) hydroxide or tetrachloride yields an orange-yellow solid, thought to be Po(Cr04)2. This is insoluble in an excess of the reagent and is easily hydrolyzed by water or wet acetone to a dark brown basic chromate with a composition close to 2Po02 Cr()3 (cf., the basic sulfate and selenate). On long standing in an excess of aqueous chromium trioxide, oxidation to polonium(VI) may occur (Section VI,A). 

The white basic selenate, 2Po02Se03, is obtained by treating polonium V) hydroxide or chloride with selenic acid (0.015 iV-5.0 N) the salt is yellow above 250°C and is stable to over 400°C. It is rather less soluble than the basic sulfate, but the solubility increases a hundredfold in passing from 0.05 N to 5 N selenic acid (10), indicating complex ion formation. 

The white basic sulfate, 2Po02-S03, results when polonium(IV) hydroxide or chloride is treated with 0.02 N-0.25 N sulfuric acid. Like the selenate, it is yellow above 250°C and decomposes to the dioxide at 550°C. Solubility studies indicate that it is metastable in contact with 0.1 N-0.5 N sulfuric acid (10). 

The salts 2Po02-X03 (X=S, Se) have been reported to form when the tetrachloride or hydroxide of polonium is treated with more dilute acid (0.02-0.25 N). The basic sulfate is yellow in color, while the selenate is white. 

Sauerstoff ist unter Normalbedingungen ein Gas, Schwefel und Selen sind kovalente Feststoffe, Tellur ist ein Halbmetall und Polonium ist ein Metall. 

---