Lanthanides
Lanthanum
The first rare-earth element, used in camera lenses.
Atomic #57Mass138.91Blockf-blockPeriod6Group—
La57 · 138.91
3D Atom Explorer
Inside the Lanthanum atom
Switch between Bohr and Quantum Cloud modes to compare a simple teaching model with a more realistic probability-based view, and follow the guided tour to explore the Lanthanum atom step by step.
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Electron configuration
[Xe] 5d1 6s2
A neutral Lanthanum atom has 57 electrons (equal to its proton count). Choosing a different isotope above changes only the neutron count.
Shell distribution
Shell 12 e⁻Shell 28 e⁻Shell 318 e⁻Shell 418 e⁻Shell 59 e⁻Shell 62 e⁻
Electrons fill inner shells before outer ones; the outermost (valence) shell drives the element's chemistry.
Properties
Physical & atomic properties
- State (room temp)
- Solid
- Melting point
- 1193 K (920 °C)
- Boiling point
- 3737 K (3464 °C)
- Density
- 6.145 g/cm³
- Electronegativity
- 1.1 Pauling
- Atomic radius
- 195 pm
- 1st ionization energy
- 538 kJ/mol
- Category
- Lanthanides
History
Discovery & naming
- Discovered
- 1839
- Discovered by
- Carl Gustaf Mosander
- Origin of name
- Greek 'lanthanein', meaning to lie hidden.
Notable uses
Camera lenses, hybrid-car batteries, and catalysts.
Cosmic origin
Where Lanthanum comes from
Stellar fusion and dying stars
An important source is slow neutron capture in dying low-mass stars.
Simplified origin map — many elements form through more than one astrophysical pathway.
Summary
- Atomic number
- 57
- Atomic mass
- 138.91
- Category
- Lanthanides
- Group · Period
- — · 6
- Block
- f-block
- Shells
- 2 · 8 · 18 · 18 · 9 · 2