Tellurium trioxide, TeO

Tellurium trioxide, TeOs, is made by carefully heating H2TeO< to a red heat. It is an orange-yellow crystalline substance, sparingly soluble in water, and easily decomposed by heat, forming the dioxide and oxygen. 

Tellurium burns in air with a greenish-blue flame. The combustion product is dioxide, Te02, the most stable oxide of the metal. Tellurium also forms other oxides the monoxide, TeO, the trioxide, TeOs, and the pentoxide, Te205. Monoxide has not yet been obtained in solid form. Like sulfur and selenium, tellurium forms oxyacids. Such oxyacids include orthotelluric acid, HeTeOe and tellurous acid, H2Te03, in which the metal is in +6 and +4 valence states respectively. 

Oxygen forms three oxides, TeO, Te02, and TeOj. The first two are somewhat basic in nature and are represented by numerous salts in which tellurium is bivalent or quadrivalent, respectively. The dioxide and the trioxide are both mainly acidic in character, although a few hexavalent salts of tellurium are known. 

Tellurium sulfoxide, TeSOj, may be made by direct union of tellurium and sulfur trioxide or by dissolving tellurium in strong sulfuric acid with gentle warming. It forms a red solution which on further heating yields a colorless solution, which is the basic sulfate. The sulfoxide forms a red amorphous solid, which on heating to 230° loses SO2 and leaves behind TeO. 

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