91Ó°ÊÓ

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 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 \(\text{A}_{2}, \text{B}_{2}\), and \(\text{C}_{2}\) can all act as oxidizing agents. In solution, \(\text{A}_{2}\) is green, \(\text{B}_{2}\) is yellow, and \(\text{C}_{2}\) is red. In the reactions in which they participate, they are reduced to \(\text{A} ^{-}\). \(\text{B} ^{-}\), and \(\text{C}^{-}\) ions, all of which are colorless. When a solution of \(\text{C}_{2}\) is mixed with one containing \(\text{A}^{-}\) ions, the color changes from red to green. Which species is oxidized? ____________ Which is reduced? ______________ When a solution of \(C_{2}\) is mixed with one containing \(B^{-}\) 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 \(\text{A}_{2}, \text{B}_{2},\) and \(\text{C}_{2}\) in order of increasing strength as an oxidizing agent. \(\frac{}{\text{Weakest oxidizing agent}} < \frac{}{\quad\quad\quad\quad\quad} < \frac{}{\text{Strongest oxidizing agent}}\)