Predict the state of astatine at room temperature?

• A. Solid
• B. Gas
• C. Liquid
• D. Plasma

Answer: (A)

The state at room temperature follows a trend for the halogens: as you go down the group, melting and boiling points rise because larger atoms with more electrons have stronger London dispersion forces. Fluorine and chlorine are gases, bromine is a liquid, and iodine is a solid at room temperature. Astatine is even heavier, so its melting point is predicted to be well above room temperature. That means astatine would be a solid when left at room temperature. (Its radioactivity and scarcity mean we rely on trends rather than direct measurements, but the pattern clearly points to a solid.)