Element 57 · Lanthanide
Lanthanum (La) — Element 57
Greek lanthanein — to lie hidden
Lanthanum (La) is a lanthanide in Period 6 (f-block) of the periodic table with atomic number 57, standard atomic weight 138.91 u, and ground-state electron configuration [Xe] 5d¹ 6s². At standard temperature and pressure it is classified as a solid with 3 valence electrons and common oxidation states +3.
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What are the atomic properties and physical constants of Lanthanum?
Reference constants compiled from IUPAC standard atomic weights, the NIST Atomic Spectra Database, and the CRC Handbook.
- Atomic number (Z)
- 57
- Standard atomic mass
- 138.91 u
- Chemical family
- Lanthanide
- Ground-state configuration
- [Xe] 5d¹ 6s²
- Electrons per shell
- 2, 8, 18, 18, 9, 2
- Valence electrons
- 3
- Common ion charges / oxidation states
- +3
- Phase at STP
- Solid
- Pauling electronegativity
- 1.10 Pauling
- First ionization energy
- 538 kJ/mol
- Atomic radius
- 240 pm
- Melting point
- 920 °C
- Boiling point
- 3,464 °C
- Discovery year
- 1839
- Table coordinate
- Period 6, f-block
- Radioactivity
- Has stable isotope(s)
How are electrons arranged across Lanthanum’s shells?
A neutral Lanthanum atom contains 57 electrons distributed across 6 occupied principal energy shells ([Xe] 5d¹ 6s²). The table below compares Lanthanum’s shell occupancy against each shell’s theoretical 2n² capacity.
| Principal Shell (n) | Spectroscopic Letter | Electrons in La | Max Shell Capacity (2n²) |
|---|---|---|---|
| n = 1 | K | 2 e⁻ | 2 e⁻ |
| n = 2 | L | 8 e⁻ | 8 e⁻ |
| n = 3 | M | 18 e⁻ | 18 e⁻ |
| n = 4 | N | 18 e⁻ | 32 e⁻ |
| n = 5 | O | 9 e⁻ | 50 e⁻ |
| n = 6 | P | 2 e⁻ | 72 e⁻ |
Frequently Asked Questions about Lanthanum (La)
What is the atomic mass and atomic number of Lanthanum (La)?
Lanthanum (La) has atomic number Z = 57 (57 protons in its nucleus) and an IUPAC standard atomic weight of 138.91 u. It sits in Period 6 in the f-block and is classified as a lanthanide.
What is the ground-state electron configuration of Lanthanum?
The neutral ground-state electron configuration of Lanthanum (Z = 57) is [Xe] 5d¹ 6s². Across its 6 occupied principal shells (n = 1 to n = 6), the electrons per shell are 2, 8, 18, 18, 9, 2, with 3 valence electrons participating in bonding.
What are the common ion charges and electronegativity of Lanthanum?
Lanthanum commonly forms +3 oxidation states or ion charges in compounds. Its Pauling electronegativity is 1.10 and its first ionization energy is 538 kJ/mol.
When was Lanthanum discovered and what is it used for?
Lanthanum was discovered in 1839 (Greek lanthanein — to lie hidden). Camera lenses, hybrid batteries
How does Lanthanum compare to neighboring elements?
Other lanthanide elements: