81 2 · 8 · 18 · 32 · 18 · 3

Thallium, Tl, element 81

Post-transition metal· Period 6· Group 13· p-block

Configuration [Xe]4f¹⁴5d¹⁰6s²6p¹

Atomic weight: 204.38Da
Phase: solid
Density: 11.8g/cm³
Melting point: 577.15K 304 °C
Boiling point: 1,746.15K 1,473 °C
Electronegativity: 1.8

Pure, unreacted thallium appears silvery-white and exhibits a metallic lustre. Upon reacting with air, it begins to turn bluish-grey and looks like lead. It is very malleable, and can be cut with a knife. There are two stable isotopes, and four radioisotopes, Tl-204 being the most stable with a half-life of 3.78 years. Thallium sulphate was used as a rodenticide. Thallium sulphine's conductivity changes with exposure to infrared light, this gives it a use in infrared detectors. Discovered by Sir William Crookes via spectroscopy. Its name comes from the Greek word thallos, which means green twig. Thallium and its compounds are toxic and can cause cancer. Description from mendeleev.

Back to the table

The outermost shell: the valence electronsThe inner shellsThe nucleus One bead for each electron, on the ring of its shell, counted from the nucleus out. The rings turn at their own pace; the model is Bohr's picture of the atom, which places electrons in shells but not on true orbits.

Atomic properties

4 of 5 fields have a value for thallium

Atomic weight The standard atomic weight. For an element with no stable isotope, the mass of its longest-lived isotope.: 204.38Da; Source: mendeleev
Electron configuration: [Xe]4f¹⁴5d¹⁰6s²6p¹; Source: mendeleev
Electron configuration in full The electron configuration with the noble-gas core written out.: 1s²2s²2p⁶3s²3p⁶3d¹⁰4s²4p⁶4d¹⁰4f¹⁴5s²5p⁶5d¹⁰6s²6p¹; Source: Worked outfrom electron configuration
Electrons in each shell Counted from the electron configuration, from the first shell outward.: 2 · 8 · 18 · 32 · 18 · 3; Source: Worked outfrom electron configuration

No data uncertainty of the atomic weight.

Screening of each subshell

Clementi's screening constants: how much of the nucleus's charge the other electrons hide from an electron in each subshell. What is left is the effective nuclear charge it feels.

Subshell	Screening σ	Effective charge Z − σ
1s	1.5591	79.4409
2s	21.3158	59.6842
2p	4.5138	76.4862
3s	23.5809	57.4191
3p	22.6335	58.3665
3d	13.4658	67.5342
4s	34.9212	46.0788
4p	35.7832	45.2168
4d	37.6112	43.3888
4f	38.1324	42.8676
5s	51.878	29.122
5p	53.9115	27.0885
5d	58.975	22.025
6s	68.1804	12.8196
6p	68.7462	12.2538