CAS Number7440-71-3
PubChem CIDna
Atomic Radius-
Atomic Volume18.4
Atomic Weight[251]
Boiling Point-
Bulk Modulus
Crystal StructureSimple Hexagonal
Covalent Radius-
Electrical Resistivity
Electron Configuration[Rn] 5f10 7s2
Electrons per shell2, 8, 18, 32, 28, 8, 2
Heat of Fusionna
Heat of Vaporizationna
Ionization Potential6.282
Magnetic Ordering
Magnetic Susceptibility
Mass Number98
Melting Point900
Atomic Number251
Oxidation States2, 3, 4
Poisson Ratio
Shear Modulus
Specific Heat Capacity-
Thermal Conductivity0.1
Van der Waals radius
Young's Modulus
Abundance in Earth's crustna
Abundance in Universena
Cf Calafoirniam 98 (251) 7 f 98 [Rn] 5f10 7s2 2 8 18 32 28 8 2 None Unknown 1.3 {"1":"608"} 608 3 10.0 1 900.6 y 1.3×103y AlphaEmission Solid, Actinide, Radioactive, Synthetic kal-eh-FOR-ni-em Synthetic radioactive metal. Powerful neutron emitter. It has no significant commercial applications. Made by bombarding curium with helium ions. eG6HyPrTccI Californium
Thallium was discovered spectroscopically by Sir William Crookes in 1861, in London.

In 1862, Claude-Auguste Lamy used a spectrometer to determine the composition of a selenium-containing substance which was deposited during the production of sulfuric acid from pyrite.

He noticed the new green line in the spectra and concluded that a new element was present. From Greek thallos, meanin a green shoot or twig 98 1950 Glenn T. Seaborg, Stanley G. Thompson, Albert Ghiorso, Kenneth Street USA Named after the State and University of "California", USA

Isotopes of Thallium

Standard Atomic Weight

Stable Isotopes

Unstable Isotopes

237Cf 238Cf 239Cf 240Cf 241Cf 242Cf 243Cf 244Cf 245Cf 246Cf 247Cf 248Cf 249Cf 250Cf 251Cf 252Cf 253Cf 254Cf 255Cf 256Cf

Thallium and its compounds are highly toxic
Agatha Christie made use of thallium's toxicity in her novel The Pale Horse
Thallium selenide has been used in a bolometer for infrared detection.

Thallium is also used in gamma radiation detection equipment.


Some of the electrodes in dissolved oxygen analyzers contain thallium.