Thallium, Tl

Thallium is a chemical element with the symbol Tl and atomic number 81. This soft gray malleable poor metal resembles tin but discolors when exposed to air. Approximately 60-70% of thallium production is used in the electronics industry, and the rest is used in the pharmaceutical industry and in glass manufacturing. It is used in infrared detectors. Thallium is highly toxic and is used in rat poisons and insecticides. Since it may cause cancer[citation needed] (although the United States EPA does not class it as carcinogen), its use has been cut back or eliminated in many countries. It is used in murders and has the nicknames "The Poisoner's Poison" and "Inheritance powder" (alongside arsenic).

This metal is very soft and malleable and can be cut with a knife. When it is first exposed to air, thallium has a metallic luster but quickly tarnishes with a bluish-gray tinge that resembles lead (it is preserved by keeping it under oil). A heavy layer of oxide builds up on thallium if left in air. In the presence of water, thallium hydroxide is formed.

Technical Data
Symbol Tl Density (20°C)/gcm3 11.85
Atomic number 81 Melting point / °C 303.5
No. of naturally occurring isotopes 2 Boiling point / °C 1457
Atomic weight 204.383 ΔHfus/kJmol-1 4.31
Electronic configuration [Xe]4f145d106s26p1 ΔHvap/kJmol-1 166.1
Metal radius(6-coordinate)/pm 170 ΔHf(monoatomic gas)/kJmol-1 180.7
Ionic radius(6-coordinate)/pm III 88.5 Electrical resistivity (20°C)/μohm cm 18
Ionic radius(6-coordinate)/pm I 150 Ionization energy/kJmol-1 I 589.1
E° (M3+(aq)\ + 3e- →M(s))/V 1.26 Ionization energy/kJmol-1 II 1970.5
E° (M+(aq)\ + e- →M(s))/V -0.34 Ionization energy/kJmol-1 III 2877.4
Electronegativity χ 1.8 Hardness (Mohs) 1.2-1.3
Evaporation Techniques
Temperature (oC) @Vap. Pressure Techniques Remarks
10-8 Torr 10-6 Torr 10-4 Torr Electron Beam Crucible Coil Boat
280 360 470 Poor Al2O3 & Quartz - Tungsten & Tantalum Wets freely, very toxic

Evaporation Materials
T4-5001-M pieces 6mm and smaller
T4-2000-R 0.500" (12.7mm)