Nonmetal are called "metalloids" mainly in light of their physical resemblance to metals. While they each have a metallic appearance, they are brittle and only fair conductors of electricity. Boron, silicon, germanium, tellurium are semiconductors. Arsenic and antimony have the electronic band structures of semimetals although both have less stable semiconducting allotropes. Astatine has been predicted to have a metallic crystalline structure. Chemically the metalloids generally behave like (weak) nonmetals. They have moderate ionisation energies, low to high electron affinities, moderate electronegativity values, are poor to moderately strong oxidising agents, and demonstrate a tendency to form alloys with metals. The reactive
Tellurium hexafluoride Tellurium hexafluoride Tellurium hexafluoride is a chemical compound of tellurium and fluorine with the chemical formula TeF. It is a colorless, highly toxic gas with an extremely unpleasant smell. Tellurium hexafluoride is most commonly prepared by passing fluorine gas over tellurium at 150 °C. Below this temperature a mixture of lower fluorides form, including tellurium tetrafluoride and ditellurium decafluoride. It can also be prepared by passing fluorine gas over TeO or indirectly by reacting TeO with SeF to produce TeF and then heating TeF in excess of 200 °C to make TeF and Te. Tellurium hexafluoride is a highly symmetric