Thallium

General
Name, Symbol, Number	Thallium, Tl, 81
Chemical series	True metals
Group, Period, Block	13 (IIIA), 6 , p
Density, Hardness	11850 kg/m3, 1.2
Appearance	Silvery white
Atomic Properties
Atomic weight	204.3833 amu
Atomic radius (calc.)	190 (156) pm
Covalent radius	148 pm
van der Waals radius	196 pm
Electron configuration	[Xe]44f14 5d10 6s2 6p1
e- 's per energy level	2, 8, 18, 32, 18, 3
Oxidation states (Oxide)	3,1 (mildly basic)
Crystal structure	Hexagonal
Physical Properties
State of matter	solid
Melting point	577 K (579 °F)
Boiling point	1746 K (2683 °F)
Molar volume	17.22 ×1010-3 m3/mol
Heat of vaporization	164.1 kJ/mol
Heat of fusion	4.142 kJ/mol
Vapor pressure	5.33 E-06 Pa at 577 K
Speed of sound	818 m/s at 293.15 K
Miscellaneous
Electronegativity	1.62 (Pauling scale)
Specific heat capacity	129 J/(kg*K)
Electrical conductivity	6.17 106/m ohm
Thermal conductivity	46.1 W/(m*K)
1st ionization potential	589.4 kJ/mol
2nd ionization potential	1971 kJ/mol
3rd ionization potential	2878 kJ/mol
Most Stable Isotopes
iso NA half-life DM DE MeV DP 203Tl 29.524% Tl is stable with 122 neutrons 204Tl {syn.} 3.78 y Beta- Epsilon 0.764 0.347 204Pb 204Hg 205Tl 70.476% Tl is stable with 124 neutrons
SI units & STP are used except where noted.

Thallium is a chemical element in the periodic table that has the symbol Tl and atomic number 81. This soft gray malleable true metal resembles tin but discolors when exposed to air. Thalium is highly toxic and is used in rodent and insect poisons but since it can also cause cancer, this use has been cut back or eliminated in many countries. It is also used in infrared detectors.

Table of contents

1 Notable Characteristics 2 Applications 3 History 4 Occurrence 5 Isotopes 6 Precautions 7 External Links

Notable Characteristics

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

Applications

The odorless and tasteless thallium sulfate was widely used in the past as a rat poison and ant killer. In the United States and many other countries, this use is no longer allowed due to safety concerns, however. Other uses;

• thallium sulfide's electrical conductivity changes with exposure to infrared light therefore making this compound useful in photocells.
• thallium bromide-iodide crystals have been used as infrared optical materials.
• thallium oxide has been used to manufacture glasses that have a high index of refraction.
• used in semiconductor materials for selenium rectifiers,
• in gamma radiation detection equipment,
• high-density liquid used for sink-float separation of minerals,
• used in the treatment of ringworm and other skin infections. However this use has been limited due to the narrow margin that exists between toxicity and therapeutic benefit.
• radioactive thallium-201 is used for diagnostic purposes in nuclear medicine, particularly in stress tests used for risk stratification in patients with coronary artery disease (CAD).
• combined with sulfur or selenium and arsenic, thallium has been used in the production of high-density glasses that have low melting points in the range of 125 and 150 °C. These glasses have room temperature properties that are similar to ordinary glasses and are durable, insoluble in water and have unique refractive indexes.

In addition, research activity with thallium is ongoing to develop high-temperature superconducting materials for such applications as magnetic resonance imaging, storage of magnetic energy, magnetic propulsion, and electric power generation and transmission.

History

Thallium (Greek thallos meaning "a green shoot or twig") was discovered by Sir William Crookes in 1861 in England while he was making spectroscopic determinations for tellurium on residues from a sulfuric acid plant. The name comes from Thallium's bright green spectral emission lines. In 1862 Crookes and Claude-Auguste Lamy isolated the metal independent of each other.

Occurrence

Although the metal is reasonably