Lanthanum

Chaitra 26/06/2026 19:58:08 Updated 26/06/2026 19:58:08

Property	Value
Atomic Number	57
Element	Lanthanum
Symbol	La
Atomic Mass	138.905 u
Number of Neutrons	82 (most common isotope, Lanthanum-139)
Number of Protons	57
Number of Electrons	57
Period	6
Group	3
Phase	Solid
Radioactive	No (La-138 is weakly radioactive but occurs naturally)
Natural	Yes
Metal	Yes
Nonmetal	No
Metalloid	No
Type	Lanthanide
Atomic Radius	240 pm
Electronegativity	1.10 (Pauling scale)
First Ionization Energy	5.577 eV
Density	6.15 g/cm³
Melting Point	920 °C
Boiling Point	3464 °C
Number of Isotopes	2 naturally occurring (La-138, La-139)
Discoverer	Carl Gustaf Mosander
Year	1839
Specific Heat	0.195 J/g·K
Number of Shells	6
Number of Valence Electrons	3