Chapter 12

As pure elements, all of the halogens are diatomic molecular species. Their melting points are: \(\mathrm{F}_{2}, 85 \mathrm{K}\) \(\mathrm{Cl}_{2}, 239 \mathrm{K}, \mathrm{Br}_{2}, 332 \mathrm{K},\) and \(\mathrm{I}_{2}, 457 \mathrm{K} .\) Using the Periodic Table, predict as best you can the molecular formula of elemental 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, B, and C can all act as oxidizing agents. In solution, A is green, B is yellow, and C is red. In the reactions in which they participate, they are reduced to \(A^{-}, B^{-},\) and \(C^{-}\) ions, all of which are colorless. When a solution of \(C\) 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 \(C\) is mixed with one containing \(A^{-}\) ions, the color remains red. Is \(\mathrm{C}\) a better oxidizing agent than \(\mathrm{A} ?\) _____ Is \(\mathrm{C}\) a better oxidizing agent than \(\mathrm{B} ?\) _____ Arrange \(\mathrm{A}, \mathrm{B},\) and \(\mathrm{C}\) in order of increasing strength as an oxidizing agent.