Thallium Tl (Element 81) of Periodic Table

81 Tl (Thallium)

Appearance:  Silvery white

Mass number:  204

Standard Atomic weight:  204.38 g/mol

Atomic number (Z):  81

Electrons:  81

Protons:  81

Neutrons:  123

Group:  13

Period:  6

Block:  p

Element category:  Post-transition metal

Electrons per shell:  K2, L8, M18, N32, O18, P3

Electron Configuration:  1s22s22p63s23p63d104s24p64d105s25p64f145d106s26p1

Phase:  solid

Melting point:  577 K (304 oC)

Boiling point:  1746 K (1473 oC)

Density:  11.85 g/cm3 (in solid) , 11.22 g/cm3(in Liquid at m.p)

Neutron cross section (Brans):  3.4

Heat of fusion:  4.14 kJ/mol

Heat of vaporization:  165 kJ/mol

Molar heat capacity:  26.32 J/(mol∙K)

Molar volume:  0.000017248

Oxidation states:  3, 2, 1, -1, -2, -5

Ion charge:  Tl+, Tl3+

Electronegativity:  pauling scale; 1.62

Valence:  3

Electron affinity:  19.2 kJ/mol

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

Vander waals radius:  196 pm

Crystal structure:  Hexagonal close-packed

Grid parameters:  a=3.456 c=5.525

Attitude c/a:  1.599

Debye temperature:  96 K (-177.15 oC)

Sound speed:  818 m/s

Thermal expansion:  29.9 μm/(m∙K)

Thermal conductivity:  46.1 W/(m∙K)

Electrical resistivity:  0.18 μΩ∙m

Magnetic ordering:  Diamagnetic

Magnetic Susceptibility:  -50.9×10-6 cm3/mol

Volume magnetic susceptibility:  -0.0000356

Mass magnetic susceptibility:  -3×10-9 m3/kg

Molar magnetic susceptibility:  -6.13×10-10 m3/mol

Superconducting point:  2.38 K (270.77 oC)

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

Naming:  After Greek thallos

Discovery:  William Crookes (1861)

First isolation:  Claude-Auguste Lamy (1862)

Isotopes:  203Tl 204Tl 205Tl

 Uses of Thallium

Thallium sulfate was employed as a rodent(Rat) killer, Household use this poison has been prohibited in most developed countries. Thallium is mostly used photoelectric cells and Thallium oxide is used  to produce special glass with a high index refrection.

Biological role of Thallium: 

It is very toxic and there is evidence that the vapour is both teratogenic and carcinogenic. It can affecting the central nervous system of body.

Natural abundance: 

It is found in several ores like pyrites, which is used to produce sulphuric acid. But Thallium is mainly obtained as a by-product of copper, zinc and lead refining. Thallium is also present in manganese nodules found on the ocean floor.


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