Atomic number:81

Group numbers:13

Period:6

Electronic configuration:[Xe] 4f¹⁴ 5d¹⁰ 6s² 6p¹

Formal oxidation number:+1 +3

Electronegativities:1.8

Atomic radius / pm:170

Relative atomic mass:204.3833 ± 0.0002

 

Thallium was discovered by Sir William Crookes (GB) in 1861. The origin of the name comes from the Greek word thallos meaning green twig or green shoot. It is a soft grey metal that looks like lead and tarnishes in moist air. Thallium reacts in heated moist air and in acids. Its compounds are highly toxic by inhalation or ingestion and have a cumulative effect. Thallium is found in iron pyrites, in crookesite, hutchinsonite and lorandite. Most is recovered from the by-products of lead and zinc refining. Its compounds are used in rat and ant poisons and for detecting infrared radiation.

Density / g dm^-3:11850 (293 K)

 11290 (m.p.)

Molar volume / cm³mol^-1:17.25 (293 K)

 18.10 (m.p.)

Electrical resistivity / μΩcm:18 (20 °C)

Thermal conductivity / W m^-1K^-1:46.1

Melting point / °C:304

Boiling point / °C:1473

Heat of fusion / kJ mol^-1:4.31

Heat of vaporization / kJ mol^-1:166.1

Heat of atomization / kJ mol^-1:182.845

1st ionization energy / kJ mol^-1:589.36

2nd ionization energy / kJ mol^-1:1971.02

3rd ionization energy / kJ mol^-1:2878.18

in the atmosphere / ppm:-

in the Earth's crust / ppm:0.36

in the oceans / ppm:0.00001