Chapter 12

As pure elements, all of the halogens are diatomic molecular species. Their melting points are: \(\mathrm{F}_{2}, 54 \mathrm{K}\) \(\mathrm{Cl}_{2}, 172 \mathrm{K} ; \mathrm{Br}_{2}, 266 \mathrm{K} ;\) and \(\mathrm{I}_{2}, 387 \mathrm{K} .\) Using the Periodic Table. predict as best you can the molecular formula of clemental astatine, At, the only radioactive element in this family. Also predict whether it will be a solid, liquid, or gas at room temperature. Elemental formula: _________ Phase at room temperature: _______ .

Substances \(A_{2}, B_{2}\), and \(C_{2}\) can all act as oxidizing agents. In solution, \(A_{2}\) is green, \(B_{2}\) is yellow, and \(C_{2}\) is red. In the reactions in which they participate, they are reduced to A^{ - } \(, B^{2}\), and \(C\) - ions, all of which are colorless. When a solution of \(C_{2}\) is mixed with one containing \(B^{-}\) ions, the color changes from red to yellow. Which species is oxidized?_________ . Which is reduced? _______ . When a solution of \(C_{2}\) is mixed with one containing \(A^{-}\) ions, the color remains red. Is \(C_{2}\) a better oxidizing agent than \(A_{2} ?\) _______ . Is \(C_{2}\) a better oxidizing agent than \(B_{2} ?\) ________ . Arrange \(A_{2}, B_{2},\) and \(C_{2}\) in order of increasing strength as an oxidizing agent. __________ < ___________ < _________ .