Lanthanum (La)
Element 57 · Lanthanide · atomic mass 138.91 u · f-block, period 6
Electron shells: 2, 8, 18, 18, 9, 2
Lanthanum heads the rare-earth series and is neither rare nor especially exotic. It gives camera glass a high refractive index and low dispersion.
Its first real job was making gas-lantern mantles glow brightly in the 1880s.
- Atomic number
- 57
- Atomic mass
- 138.91 u
- Electron configuration
- [Xe] 6s² 5d¹
- Group · period · block
- f-block · 6 · f
- Oxidation states
- +3
- Electronegativity
- 1.1 (Pauling)
- Melting point
- 918 °C
- Boiling point
- 3,464 °C
- Density
- 6.15 g/cm³
- State at 20 °C
- Solid
- Appearance
- Silvery-white, malleable metal
- Discovered
- Carl Gustaf Mosander, 1839
57 protons, and 57 electrons when neutral
IUPAC standard atomic weight
Shown in the strip below the table
What Lanthanum is used for
- High-quality camera and telescope lenses
- Nickel-metal-hydride battery electrodes
- Petroleum cracking catalysts
- Carbon-arc studio lighting
Atomic structure of Lanthanum
A neutral lanthanum atom has 57 protons and 57 electrons. Its most common isotope carries about 82 neutrons, which is where the mass number 139 comes from. Change the neutron count and you have a different isotope of lanthanum; change the proton count and you have a different element entirely.
Those electrons fill shells from the inside out: 2, 8, 18, 18, 9, 2. In orbital notation that is [Xe] 6s² 5d¹. As a f-block element its valence count is variable, which is why it can form compounds in several oxidation states.
3D electron orbitals
See where Lanthanum's electrons actually are — a cloud of 26,000 points sampled from the probability density |ψ|², not a cartoon of a lobe.
Where Lanthanum sits in the periodic table
Discovery and naming
Lanthanum was discovered by Carl Gustaf Mosander in 1839. Its name comes from Greek lanthanein, "to lie hidden".
Keep exploring
Atomic weight from IUPAC/CIAAW; physical properties from PubChem (US National Library of Medicine). Values that have never been measured are shown as “not measured” rather than estimated.
Related Calculators
Frequently Asked Questions
What is the atomic mass of Lanthanum?
The standard atomic weight of Lanthanum is 138.91 u, as published by IUPAC's Commission on Isotopic Abundances and Atomic Weights.
How many protons, neutrons and electrons does Lanthanum have?
Lanthanum has 57 protons, because the atomic number is the proton count and that is what makes an atom Lanthanum at all. A neutral Lanthanum atom has the same number of electrons, 57. The neutron count varies by isotope; the most common one has about 82, since 139 − 57 = 82.
What is the electron configuration of Lanthanum?
The electron configuration of Lanthanum is [Xe] 6s² 5d¹. Its electrons are arranged 2, 8, 18, 18, 9, 2 across 6 shells.
Is Lanthanum a metal?
Yes. Lanthanum is classified as a lanthanide, on the metallic side of the table.
What group and period is Lanthanum in?
Lanthanum sits in the f-block strip below the main table, in period 6, among the lanthanides. Elements in that strip are not given a group number in the standard 18-column layout.
What is the charge of Lanthanum?
Lanthanum most commonly forms a 3+ ion. Like most transition metals it has several accessible oxidation states, so the charge depends on the compound.
What is the melting point of Lanthanum?
Lanthanum melts at 918 °C and boils at 3,464 °C. That puts it in the solids at everyday temperatures.
What is Lanthanum used for?
High-quality camera and telescope lenses, Nickel-metal-hydride battery electrodes, Petroleum cracking catalysts, Carbon-arc studio lighting. Lanthanum heads the rare-earth series and is neither rare nor especially exotic.
Who discovered Lanthanum, and where does its name come from?
Lanthanum (La) was discovered by Carl Gustaf Mosander in 1839. The name comes from Greek lanthanein, "to lie hidden".