SymbolTl
Latin nameThallium
Atomic number81
Period6
Element categoryMetals
Relative atomic mass204.3833
GroupIII.A
Electronegativity
1.8
Oxidation numbers
1, 3
Electron configuration
1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 5s2 5p6 4f14 5d10 6s2 6p1
Density [g/cm3]
11.85
State
Solid
Melting point [°C]
303.5
Boiling point [°C]
1457
Thermal conductivity [W m-1K-1]
46.1
Heat capacity [J K-1g-1]
0.129
Discovery
1861
Hardness [Mohs scale]
1.2
Young's modulus [GPa]
8
Electrical conductivity [S m-1]
5.6 · 106
Shear modulus [GPa]
2.8
1.st ionization energy [eV]
6.1083
2.nd ionization energy [eV]
20.428
3.rd ionization energy [eV]
29.829
Stable isotopes
2
Unstable isotopes
26