Lanthanum
(From the Greek word lanthanein, to line hidden) Silvery metallic element belonging to group 3 of the periodic table and oft considered to be one of the lanthanoids. Found in some rare-earth minerals. Twenty-five natural isotopes exist. La-139 which is stable, and La-138 which has a half-life of 10^10 to 10^15 years. The other twenty-three isotopes are radioactive. It resembles the lanthanoids chemically. Lanthanum has a low to moderate level of toxicity, and should be handled with care. Discovered in 1839 by C.G. Mosander.
Gallery
Jurii, CC BY 3.0 <https://creativecommons.org/licenses/by/3.0>, via Wikimedia Commons, source: https://images-of-elements.com/lanthanum.php
Physical Propertiesmass · density · phase · crystal
Atomic Mass
138.9055Da
Density
6.1500g/cm³
Phase (STP)
Solid
Melting Point
1193.2K
Boiling Point
3737.2K
Molar Heat
0.1950J/(mol·K)
Crystal Structure
HEX
Lattice Constant
3.750Å
Atomic Radiiatomic · covalent · van der Waals
Atomic (Empirical)
195.00pm
Covalent
180.00pm
Van der Waals
243.00pm
Electronic Propertieselectronegativity · ionization · affinity
Electron Configuration
[Xe] 5d 6s2
Electron Shells
2, 8, 18, 18, 9, 2
Electronegativity
1.10Pauling
Electron Affinity
0.5kJ/mol
1st Ionization Energy
5.6kJ/mol
Oxidation States
+2, +3
Orbital DiagramAufbau · Hund's rule · Pauli exclusion
Full: 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 5s2 5p6 5d1 6s2Short: [Xe] 5d 6s2
Ionization Energies (57 known)
Emission Spectrumvisible range · characteristic spectral lines
Abundanceby mass
Log scale · ppm = parts per million by mass
Biological Role
No known biological role. Low toxicity.
Discovery
Discovered By
Carl Mosander
Named By
—
Year
1839
Nuclear Data
Known Isotopes
42
Stable Isotopes
1
Stable Mass Numbers
139
Natural isotopic abundance (IUPAC recommended values)
Isotopes of La42 known
| Nuclide | Z | N | Mass (AMU) | Half-life | Decay | Jπ | Abundance |
|---|---|---|---|---|---|---|---|
| 116La | 57 | 59 | 115.957005 | Unknown | β⁺, β⁺p, p | — | — |
| 117La | 57 | 60 | 116.950326 | 21.7 ms | p (1%), β⁺, β⁺p | 3/2+ | — |
| 118La | 57 | 61 | 117.946731 | Unknown | β⁺, β⁺p | 1- | — |
| 138La | 57 | 81 | 137.907124 | 103 Gy | β⁺ (0.655%), β⁻ (0.345%) | 5+ | 8.8810% |
| 139Lastable | 57 | 82 | 138.906363 | Stable | stable (1%) | 7/2+ | 9991.1190% |
| 155La | 57 | 98 | 154.959280 | 101 ms | β⁻ (1%), β⁻n, 2n | 1/2+ | — |
| 156La | 57 | 99 | 155.964519 | 84.0 ms | β⁻ (1%), β⁻n | 4+ | — |
| 157La | 57 | 100 | 156.968792 | Unknown | β⁻, β⁻n | 1/2+ | — |