Thallium

Source of the photo
http://hu.wikipedia.org/wiki/Tallium
Author of the description
Gruiz Katalin
tallium

Atomic number

81

Atomic mass

204.383 g.mol -1

Electronegativity

1.8

Density

11.71 g.cm-3 at 20°C

Melting point

304 °C

Boiling point

1473 °C

Vanderwaals radius

0.182 nm

Ionic radius

0.099 nm

Isotopes

11

Electronic shell

[ Xe ] 4f14 5d10 6s2 6p1

Energy of first ionisation

589.1 kJ.mol -1

Energy of second ionisation

1970.5 kJ.mol -1

Energy of third ionisation

2877.4 kJ.mol -1

Discovered by

Sir William Crookes in 1861

 


When freshly exposed to air, thallium exhibits a metallic lustre, but soon develops a blueish-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.

Applications

Thallium is used for making low-melting point special glass for highly reflective lenses. Thallium salts are used as reagents in chemical research. Thallium sulphate is still sold in developing countries where it is still permitted as a pesticide, although banned in Western countries. Since its electrical conductivity changes with exposure to infrared light, it is used in photocells. It is used for sink-float separation of minerals. Thallium amalgam is used in thermometers for low temperature, because it freezes at -58 °C (pure mercury freezes at -38 °C).

Source of description

http://www.lenntech.com/periodic/elements/tl.htm

Fémek és vegyületeik