Thallium

Atomic number

81

Atomic mass (u)

204.383

Category

Post-transition metal

Standard state

Solid

Melting point

303.85 °C (577 K)

Boiling point

1472.85 °C (1746 K)

Density (g/cm³)

11.8

Electronegativity (Pauling)

1.62

Electron configuration

[Xe]6s2 4f14 5d10 6p1

Oxidation states

+3, +1

Atomic radius (pm)

196

First ionization energy (eV)

6.108

Discovery & recognition

Discovery year / period (PubChem)

1861

Discovery credited to (RSC)

William Crookes

Date or period recorded by RSC

1861

Discovery place

London, United Kingdom; subsequent isolation in Lille, France

An ancient date does not identify a first human discovery. Different references may date observation, isolation and formal recognition differently.

Natural occurrence & production

The creation of an element’s nuclei and its concentration into terrestrial deposits are different processes. The occurrence note below concerns its presence or production on Earth; it is not a complete account of nucleosynthesis.

“Thallium is found in several ores.”

Royal Society of Chemistry · occurrence excerpt ↗

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Reference values are not product specifications. Blank values have not been estimated. For superheavy elements, some properties and family assignments are theoretical or incompletely measured.