Discovered By: William Crookes
Discovery year: 1861

The following table showing some properties of Thallium(Tl):

Table Example
Atomic number 81
Group 13
Period 6
Block p
Electrons 81
Protons 81
Neutrons 123
Atomic weight 204.38
Oxidation states +1, +3
Ionic charge Tl^+, Tl^3+


Table Example
Electrons per shell K2 L8 M18 N32 O18 P3
Electron configuration 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^10 4p^6 5s^2 4d^10 5p^6 6s^2 4f^14 5d^10 6p^1
Atomic radius 156 pm
Covalent radius 145 pm
Van der Waals radius 196 pm
Boiling point 1473°C
Melting point 304°C
Phase Solid
Fusion heat 4.2 kJ.mol^-1
Vaporization heat 165 kJ.mol^-1


Table Example
Thermal expansion 2.99*10^-5 K^-1
Specific heat 129 J.kg^-1.K^-1
Color Silver
Brinell hardness 26.4 MPa
Bulk modulus 43 GPa
Density 11850 kg.m^-3
Liquid density 11220 kg.m^-3
Mohs hardness 1.2
Poisson ratio 0.45
Shear modulus 2.8 GPa


Table Example
Sound speed 818 m.s^-1
Young's modulus 8 GPa
Electrical type Conductor
Magnetic type Diamagnetic
Resistivity 1.5*10^-7 Ohm.m
Superconducting point 2.38 K
Electronegativity 1.62
Valence 3
Electron affinity 19.2 kJ.mol^-1
First ionization energy 589.4 kJ.mol^-1
Radioactive No
Neutron cross section 3.4 barn