Thallium

Thallium is at chemical element, it has symbol Tl and atomic number 81. Its standard atomic weight is 204.4. It is found in Group 15 of the periodic table. Thallium is a soft, heavy and gray metal, but can look red due to oxidation. Thallium and its compounds are extremely toxic, even more than cyanide and arsenic.

Thallium, ₈₁Tl

Thallium
Pronunciation	/ˈθæliəm/ ​(THAL-ee-əm)
Appearance	silvery white
Standard atomic weight Ar°(Tl)
	[204.382, 204.385]
Thallium in the periodic table
Hydrogen Helium Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson In ↑ Tl ↓ Nh mercury ← thallium → lead
Atomic number (Z)	81
Group	group 13 (boron group)
Period	period 6
Block	p-block
Electron configuration	[Xe] 4f14 5d10 6s2 6p1
Electrons per shell	2, 8, 18, 32, 18, 3
Physical properties
Phase at STP	solid
Melting point	577 K ​(304 °C, ​579 °F)
Boiling point	1746 K ​(1473 °C, ​2683 °F)
Density (near r.t.)	11.85 g/cm3
when liquid (at m.p.)	11.22 g/cm3
Heat of fusion	4.14 kJ/mol
Heat of vaporization	165 kJ/mol
Molar heat capacity	26.32 J/(mol·K)
Vapor pressure P (Pa) 1 10 100 1 k 10 k 100 k at T (K) 882 977 1097 1252 1461 1758
Atomic properties
Oxidation states	−5, −2, −1, +1, +2, +3 (a mildly basic oxide)
Electronegativity	Pauling scale: 1.62
Ionization energies	1st: 589.4 kJ/mol 2nd: 1971 kJ/mol 3rd: 2878 kJ/mol
Atomic radius	empirical: 170 pm
Covalent radius	145±7 pm
Van der Waals radius	196 pm
Spectral lines of thallium
Other properties
Natural occurrence	primordial
Crystal structure	​hexagonal close-packed (hcp)
Speed of sound thin rod	818 m/s (at 20 °C)
Thermal expansion	29.9 µm/(m⋅K) (at 25 °C)
Thermal conductivity	46.1 W/(m⋅K)
Electrical resistivity	0.18 µΩ⋅m (at 20 °C)
Magnetic ordering	diamagnetic
Molar magnetic susceptibility	−50.9×10−6 cm3/mol (298 K)
Young's modulus	8 GPa
Shear modulus	2.8 GPa
Bulk modulus	43 GPa
Poisson ratio	0.45
Mohs hardness	1.2
Brinell hardness	26.5–44.7 MPa
CAS Number	7440-28-0
History
Naming	after Greek thallos, green shoot or twig
Discovery	William Crookes (1861)
First isolation	Claude-Auguste Lamy (1862)
Isotopes of thallium
Main isotopes Decay abun­dance half-life (t1/2) mode pro­duct 201Tl synth 3.0421 d ε 201Hg 203Tl 29.5% stable 204Tl synth 3.78 y β− 204Pb ε + β+ 204Hg 205Tl 70.5% stable

Properties

Physical properties

Thallium is a soft, malleable, grayish post-transition metal. It can be cut with a knife at room temperature. It melts at a low temperature, 304 °C., which is typical of a post-transition metal. Thallium has 25 known isotopes and two stable (nonradioactive) ones. It is extremely toxic.

Chemical properties

A corroded thallium rod

Thallium is a moderately reactive metal. It corrodes easily in air with a color similar to lead. If it is kept in air for a long time, a large amount of thallium(I) oxide will build up. It corrodes in the presence of water to make the hydroxide. It burns with a greenish flame. It reacts with most acids.

Chemical compounds

Thallium makes chemical compounds in two oxidation states: +1 and +3. The +1 state is more common and less reactive. Its chemical compounds are very similar to potassium or silver compounds. It makes a hydroxide that in a strong base when dissolved in water. Most other transition metal and post-tranansition metal hydroxides do not dissolve in water. This reacts with carbon dioxide to make thallium(I) carbonate, which is also water-soluble and very heavy. It is the only heavy metal carbonate that can dissolve in water. Other compounds are similar to silver compounds. Thallium(I) bromide turns yellow when exposed to light, similar to silver(I) bromide. Thallium(I) sulfide is black, similar to silver(I) sulfide. The +3 state compounds are oxidizing agents. The black oxide, thallium(III) oxide and the hydroxide, thallium(III) hydroxide, are the only stable +3 compounds. They break down to oxygen and thallium(I) oxide when heated. Thallium and its compounds are rare because they are toxic and polluting.

Thallium(I) chloride

+1 compounds

+1 compounds are quite unreactive. It is the more common oxidation state. They are made when thallium dissolves in acids or corrodes in air.

• Thallium(I) bromide, yellowish solid, turns black when in light
• Thallium(I) carbonate, colorless solid, dissolves in water
• Thallium(I) chloride, colorless solid, does not dissolve in water
• Thallium(I) fluoride, colorless solid, dissolves in water
• Thallium(I) hydroxide, yellow solid, strong base, dissolves in water
• Thallium(I) iodide, yellow or red solid, does not dissolve in water
• Thallium(I) oxide, black solid, dissolves in water
• Thallium(I) sulfate, colorless solid, dissolves in water
• Thallium(I) sulfide, black solid, does not dissolve in water

+3 compounds

+3 compounds are oxidizing agents. They are quite rare.

• Thallium(III) halide, the thallium(III) fluoride, chloride, and bromide
• Thallium(III) hydroxide, white solid
• Thallium(III) oxide, white solid, semiconductor

History

Thallium was found by spectroscopy in 1861 by a bright green line in its spectrum. The main use for thallium, rat poison, was banned in many countries in the 1970s. Thallium was also used to poison people, similar to the more popular arsenic.

Occurrence

A mineral that has thallium in it

Thallium is found most in certain clays and granites. It cannot be gotten easily from these, though. Thallium is normally gotten from the waste after other ores like galena are processed. Hutchinsonite is another mineral that has thallium in it.

Preparation

When lead and zinc are taken from their ores, many impurities are left behind. Sulfuric acid is used to dissolve the thallium from it as thallium(I) sulfate. Then the thallium(I) sulfate is electrolyzed to make thallium metal.

Uses

It is used in rat poisons and insecticides. The use of thallium as a poison has been reduced or banned in many countries because these countries think that thallium might cause cancers. It is also used in infrared detectors. It has been used in some murders. Like arsenic, the use of thallium in murders has given it the name "inheritance powder". Thallium compounds are used in glass for infrared light. Thallium was also used to kill skin infections, but it is too toxic to be used for that now. A superconductor that can work at higher temperatures than normal ones do uses thallium. A radioactive thallium isotope was used for nuclear scans. An alloy of thallium and mercury has a low freezing temperature and is a liquid. A very dense solution of a thallium compound was used to test minerals for specific gravity, but it is too toxic for use.

Safety

Thallium is extremely toxic, even touching it is dangerous. Many of its salts easily dissolve. Some are colorless, tasteless, and odorless, but are very toxic. Some think that it is a carcinogen. Thallium can be a pollutant if the thallium waste from metal processing is washed away.