Thallium

81
Tl
Group
13
Period
6
Block
p
Protons
Electrons
Neutrons
81
81
123
General Properties
Atomic Number
81
Atomic Weight
204.3833
Mass Number
204
Category
Post-transition metals
Color
Silver
Radioactive
No
From Greek thallos, meanin a green shoot or twig
Crystal Structure
Simple Hexagonal
History
Thallium was discovered spectroscopically by Sir William Crookes in 1861, in London.

In 1862, Claude-Auguste Lamy used a spectrometer to determine the composition of a selenium-containing substance which was deposited during the production of sulfuric acid from pyrite.

He noticed the new green line in the spectra and concluded that a new element was present.
Electrons per shell
2, 8, 18, 32, 18, 3
Electron Configuration
[Xe] 4f14 5d10 6s2 6p1
Tl
Agatha Christie made use of thallium's toxicity in her novel The Pale Horse
Physical Properties
Phase
Solid
Density
11.85 g/cm3
Melting Point
577.15 K | 304 °C | 579.2 °F
Boiling Point
1746.15 K | 1473 °C | 2683.4 °F
Heat of Fusion
4.2 kJ/mol
Heat of Vaporization
165 kJ/mol
Specific Heat Capacity
0.129 J/g·K
Abundance in Earth's crust
0.000053%
Abundance in Universe
5×10-8%
Pure
Image Credits: Images-of-elements
Pure thallium under argon
CAS Number
7440-28-0
PubChem CID Number
5359464
Atomic Properties
Atomic Radius
170 pm
Covalent Radius
145 pm
Electronegativity
1.62 (Pauling scale)
Ionization Potential
6.1082 eV
Atomic Volume
17.2 cm3/mol
Thermal Conductivity
0.461 W/cm·K
Oxidation States
1, 3
Applications
Thallium selenide has been used in a bolometer for infrared detection.

Thallium is also used in gamma radiation detection equipment.

Thallium oxide has been used to produce glasses with a high index of refraction, and is used in the manufacture of photo cells.

Some of the electrodes in dissolved oxygen analyzers contain thallium.
Thallium and its compounds are highly toxic
Isotopes
Stable Isotopes
203Tl, 205Tl
Unstable Isotopes
176Tl, 177Tl, 178Tl, 179Tl, 180Tl, 181Tl, 182Tl, 183Tl, 184Tl, 185Tl, 186Tl, 187Tl, 188Tl, 189Tl, 190Tl, 191Tl, 192Tl, 193Tl, 194Tl, 195Tl, 196Tl, 197Tl, 198Tl, 199Tl, 200Tl, 201Tl, 202Tl, 204Tl, 206Tl, 207Tl, 208Tl, 209Tl, 210Tl, 211Tl, 212Tl