Astatine (At)

Isotopes of Astatine

Isotope Atomic Mass Half-life Mode of Decay Nuclear Spin
At-207  206.98578  1.81 hours  EC to Po-207; α to Bi-203 9/2 
At-208  207.98657 1.63 hours  EC to Po-208; α to Bi-204
At-209 208.98616 5.40 hours EC to Po-209; α to Bi-205 6
At-210 209.987126 8.10 hours EC to Po-210; α to Bi-206 5
At-211 210.98748 7.21 hours EC to Po-211; α to Bi-207 9/2



Astatine was discovered in 1940 by Dale R. Corson, Kenneth Ross MacKenzie and Emilio Segrè. Its name originates with the Greek word astatos, meaning "unstable."

Physical properties of this element have not been well investigated, due to the short half-lives of its isotopes. Astatine is volatile and may be distilled in a vacuum at room temperature in a glass apparatus; it may be condensed in a dry ice trap. It is soluble in chloroform, ether, hexane and many other organic solvents. Solubility in water should be of low order. Reactions of astatine should be similar to that of iodine; however, there is no evidence of existence of the diatomic molecule At2. Several compounds or polyanions are known. No practical uses of this element are known thus far.

Exposure to radiation may cause cancer. Studies on experimental animals show that such exposure induces tumors.

Properties of Astatine

Name Astatine 
Symbol At 
Atomic number 85 
Atomic weight 210 
Standard state Solid at 298 °K 
CAS Registry ID 7440-68-8 
Group in periodic table 17 
Group name Halogen 
Period in periodic table
Block in periodic table p-block 
Color Metallic 
Classification Semi-metallic 
Melting point 302 °C
Boiling point 230 °C
Thermal conductivity 1.7 (estimate) W/(m·K)
Electronegativity 2.2 
Heat of vaporization About 40 kJ·mol-1
Heat of fusion About 6 (per mole astatine atoms) kJ·mol-1
Density of solid 6.4 (estimated) g/cm3 
Electronic configuration [Xe]4f145d106s26p5 
Oxidation states in aqueous solution -1, 0, +5, +7
Most stable isotope At-210