When freshly exposed to air, thallium exhibits a metallic lustre, but soon develops a bluish-grey tinge, resembling lead in appearance. A heavy oxide builds up on thallium if left in air, and in the presence of water the hydroxide is formed. The metal is very soft and malleable. It can be cut with a knife.
The element and its compounds are toxic and should be handled carefully. Thallium may cause cancer.
Thallium has no biological role. Thallium compounds are extremely toxic. Their effects are cumulative and they can be absorbed though the skin. Thallium poisoning takes several days to act and it affects the nervous system.
Binary compounds with halogens (known as halides), oxygen (known as oxides), hydrogen (known as hydrides), and other compounds of thallium where known.
Isotope abundances of thallium with the most intense signal set to 100%.
Thallium has two stable isotopes and one of these, Tl-203, is used to produce one of the(workhorses( of nuclear medicine: Tl-201. Tl-201 is used extensively for imaging and in particular for perfusion tests of the myocardium. These tests are done to determine the damage to the heart from a heart attack or from heart diseases. Tl205 has been proposed as an alternative target for the production of Tl-201. Tl-205 is also used in nuclear magnetic resonance research.
Isolation: thallium metal would not normally be made in the laboratory as it is available commercially. Crude thallium is present as a component in flue dust along with arsenic, cadmium, indium, germanium, lead, nickel, selenium, tellurium, and zinc. This is done by dissolving in dilute acid, precipitating out lead sulphate, and then adding HCl to precipitate thallium chloride, TlCl. Further purification can be achieve by electrolysis of soluble thallium salts.
Density of solid: 11850 kg m-3
Molar volume: 17.22 cm3
Thermal conductivity: 46 W m‑1 K‑1
Melting point: 577 [304 °C (579 °F)] K
Boiling point: 1746 [1473 °C (2683 °F)] K
Enthalpy of fusion: 20.5 kJ mol-1
Atomic radius (empirical): 190 pm
Molecular single bond covalent radius: 144 (coordination number 3) ppm
van der Waals radius: 260 ppm
Pauling electronegativity: 1.62 (Pauling units)
Allred Rochow electronegativity: 1.44 (Pauling units)
Mulliken-Jaffe electronegativity: 1.96 (sp2 orbital)
First ionisation energy: 589.36 kJ mol‑1
Second ionisation energy: 1971.03 kJ mol‑1
Third ionisation energy: 2880.28 kJ mol‑1
Universe: 0.5 ppb by weight
Crustal rocks: 530 ppb by weight
Human: (no data) ppb by weight
