57
La
Lanthanum
138.90547
Lanthanum (La)
LanthanideGroup 3Period 6d-block-block
Lanthanum is a soft, ductile, silvery-white metallic chemical element with symbol La and atomic number 57. It tarnishes rapidly when exposed to air and is soft enough to be cut with a knife. It gave its name to the lanthanide series, a group of 15 similar elements between lanthanum and lutetium in the periodic table:it is also sometimes considered the first element of the 6th-period transition metals.
Latin name: Lanthanum
Atomic Number
57
Atomic Mass
138.90547 g/mol
Phase (STP)
Solid
Electron Config.
[Xe] 5d¹ 6s²
General
SymbolLa
Atomic Number57
Atomic Mass138.90547 g/mol
CategoryLanthanide
Group3
Period6
Blockd-block
Electron Configuration[Xe] 5d¹ 6s²
Valence Electrons3
Coloursilvery-white metallic
Appearancesilvery white
CAS NumberCAS7439-91-0
Physical Properties
Phase (STP)Solid
Density6.146 g/cm³
Melting Point919.85°C · 1687.73°F · 1193.00 K
Boiling Point3463.85°C · 6266.93°F · 3737.00 K
Atomic Properties
Atomic Radius240 pm
Electronegativity1.1 Pauling
Ionization Energy538 kJ/mol
Oxidation States+3
Ion ChargeLa3+
Thermodynamic
Molar Heat27.11 J/(mol·K)
Crystal Structure
Crystal Structurehexagonal close-packed
Mechanical Properties
Mohs Hardness2.5
Nuclear & Hazards
Half-lifestable
Abundance
In Universe0.00005999999999999999%
In Sun0.00005%
In Earth's Crust0.3400%
In Meteorites0.0002%
Discovery & History
Discovery Year1839
Discovered ByCarl Gustaf Mosander
Country of DiscoverySweden
Isotopes of Lanthanum
| Isotope | Abundance | Half-life | Decay |
|---|---|---|---|
| La-138 | 0.08881% | 1.02 × 10¹¹ years | EC, β⁺ |
| La-139 | 99.91119% | Stable | — |