Thallium (Tl)

Thallium is a chemical element of the periodic table with chemical symbol Tl and atomic number 81 with an atomic weight of 204.382 u and is classed as post-transition metal and is part of group 13 (boron group). Thallium is solid at room temperature.

Mercury Periodic table Lead

Thallium in the periodic table

Symbol	Tl
Atomic number	81
Group	13 (Boron group)
Period	6
Block	p
Classification	Post-Transition Metal

Appearance	Silvery white
Color	Silver

Number of protons	81 p⁺
Number of neutrons	123 n⁰
Number of electrons	81 e^-

From Wikipedia, the free encyclopediaThallium is a chemical element with symbol Tl and atomic number 81. This soft gray post-transition metal is not found free in nature. When isolated, it resembles tin, but discolors when exposed to air.

Physical properties

Phase at STP	Solid
Density	11.85 g/cm³
Atomic weight	204.382 u

Thermal properties

Melting point	577 K 303.85 °C 578.93 °F
Boiling point	1746 K 1472.85 °C 2683.13 °F
Heat of vaporization	162.09 kJ/mol

Atomic properties

Electronegativity (Pauling Scale)	1.62
Electron affinity	36.4 kJ/mol
Oxidation states	−5, −2, −1, +1, +2, +3 (a mildly basic oxide)
Ionization energies	589.4 kJ/mol 1971 kJ/mol 2878 kJ/mol

Electron configuration for thallium

Electron configuration

Shorthand configuration

[Xe] 4f¹⁴ 5d¹⁰ 6s² 6p¹

Electron configuration

Full configuration

1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 6s² 6p¹

Electron configuration chart

1s²
2s²	2p⁶
3s²	3p⁶	3d¹⁰
4s²	4p⁶	4d¹⁰	4f¹⁴
5s²	5p⁶	5d¹⁰
6s²	6p¹

Electrons per shell

2, 8, 18, 32, 18, 3

Valence electrons

3

Valency electrons

1,3

Bohr model

Figure: Shell diagram of Thallium (Tl) atom.

Orbital Diagram

1s

2s

2p

3s

3p

3d

4s

4p

4d

4f

5s

5p

5d

6s

6p

The history of Thallium

Discovery	William Crookes (1861)
First isolation	Claude-Auguste Lamy (1862)
Discovery of thallium Thallium (Greek θαλλός, thallos, meaning "a green shoot or twig") was discovered by William Crookes and Claude Auguste Lamy, working independently, both using flame spectroscopy (Crookes was first to publish his findings, on March 30, 1861). The name comes from thallium's bright green spectral emission lines. As both scientists discovered thallium independently and a large part of the work, especially the isolation of the metallic thallium was done by Lamy, Crookes tried to secure his own priority on the work. Lamy was awarded a medal at the International Exhibition in London 1862: For the discovery of a new and abundant source of thallium and after heavy protest Crookes also received a medal: thallium, for the discovery of the new element.

Periodic table history

Identifiers

List of unique identifiers for Thallium in various chemical registry databases

CAS Number	7440-28-0
ChemSpider ID	4514293
EC number	231-138-1
PubChem CID Number	5359464