Symbol Tl Atomic radius: pm 170 Fusion: kJ/Mole 4.14
Name Thallium Ionic radius: pm (+1)159 Boiling point: C 1473
Atomic number 81 Electron affinity 0.36 Melting point: C 304
Atomic weight 204.4 1st  ion potential 6.11 Specific Heat Cap: J/(g K) 0.13
Classification Other metal Natural form Solid Thermal Cond: W/(cm K) 0.46
Configuration [Xe]4f145d106s2p1 Crystal structure Hex Electrical Cond 0.0617
Oxidation states 1,3 Density 11.8 Abundance: mg/kg-crust 0.85
Electronegativity 1.8 Vaporization: kJ/Mole 162.1    
Sir William Crookes discovered thallium in 1861.  Crookes presumed the element was sulfur-like,but in 1862, he and Claude-Auguste Lamy independently isolated thallium. They found it to be a metal unlike the elements in the group containing sulfur. Uses - IR detectors, photocells, rat and ant poison