Physical Properties
Astatine is a highly radioactive element just below iodine in the Periodic Table.
We can guess at its physical properties by extrapolating from the halogens above it in Group 17.
#bb("Property"color(white)(mmmm)"F"color(white)(mmm)"Cl"color(white)(mmm)"Br"color(white)(mmmll)"I"color(white)(mmm)"At")#
#"State at 20 °C"color(white)(mm)"gas"color(white)(mmm)"gas"color(white)(mml)"liquid"color(white)(mmll)"solid"color(white)(mll)"solid"#
#"Colour"color(white)(mmmmm)"pale yel"color(white)(m)"grn-yel"color(white)(m) "red-brn"color(white)(mll)"purple"color(white)(m)"black"#
#"mp/°C"color(white)(mmmmm)"-220"color(white)(mmm)"-101"color(white)(mm)"-7.2"color(white)(mmll)114color(white)(mmm)220#
#"bp/°C"color(white)(mmmmml)"-188"color(white)(mmmll)"-35"color(white)(mll)58.8color(white)(mmll)184color(white)(mmm)310#
#"Density/g·cm"^"-3"color(white)(mmmmmmmmmmll)3.10color(white)(mmm)4.93color(white)(mmll)6.8#
#Δ_text(fus)H"/kJ·mol"^"-1"color(white)(ml)0.51color(white)(mmll)6.41color(white)(mll)10.57color(white)(mmm)15.52color(white)(mll)20.5#
#Δ_text(vap)H"/kJ·mol"^"-1"color(white)(m)6.62color(white)(mml)20.41color(white)(mll)29.96color(white)(mmm)41.57color(white)(mll)53.2#
Chemical properties
If astatine behaves like iodine, #"At"^"-"# should be oxidized to #"At"_2# by sulfuric acid.
#4×["2At"^"-" → "At"_2 + "2e"^"-"]#
#1×["SO"_4^"2-" + "10H"^"+" + "8e"^"-" → "H"_2"S" + 4"H"_2"O"#
#stackrel(————————————————————)("8At"^"-" + "SO"_4^"2-" + "10H"^"+" → "4At"_2 + "H"_2"S" + 4"H"_2"O")#
Add the spectator ions:
#"8At"^"-" + "SO"_4^"2-" + "10H"^"+" → "4At"_2 + "H"_2"S" + color(white)(mmmmmmmll)4"H"_2"O"#
#"8Na"^"+" +color(white)(mmml) "4SO"_4^"2-"→ color(white)(mmmmmmml)"8Na"^"+" + "4SO"_4^"2-"#
#stackrel(————————————————————)("8NaAt + 5H"_2"SO"_4 color(white)(mll)→ "4At"_2 + "H"_2"S" + "4Na"_2"SO"_4 +color(white)(mll) 4"H"_2"O")#
Here's what astatine looks like.
