Thallium

Chaitra 26/06/2026 19:58:09 Updated 26/06/2026 19:58:09

Property	Value
Atomic Number	81
Element	Thallium
Symbol	Tl
Atomic Mass	204.38 u
Number of Neutrons	123 (most common isotope, Thallium-205)
Number of Protons	81
Number of Electrons	81
Period	6
Group	13
Phase	Solid
Radioactive	No (Tl-204 is radioactive)
Natural	Yes
Metal	Yes
Nonmetal	No
Metalloid	No
Type	Post-transition Metal
Atomic Radius	156 pm
Electronegativity	1.62 (Pauling scale)
First Ionization Energy	6.108 eV
Density	11.85 g/cm³
Melting Point	304 °C
Boiling Point	1473 °C
Number of Isotopes	2 stable (Tl-203, Tl-205)
Discoverer	William Crookes
Year	1861
Specific Heat	0.129 J/g·K
Number of Shells	6
Number of Valence Electrons	3