Recognised as Chemical element
Lanthanum
- La
- Z = 57
- lanthanide
Lanthanum (La) is element 57, a lanthanide in period 6. Its standard atomic weight is 138.91 Da. Weights follow IUPAC standard atomic weights, 2021 revision.
Identity
SymbolLa
Standard atomic weight138.91atomic mass units (Da)
Mass in kilograms2.3066548 × 10^-25
Categorylanthanide
GroupLanthanide/actinide series, with no group number
Period6
Blockf-block
Electrons in a neutral atom57
Neutrons in the most common isotope82≈
Electron configuration
Configuration1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁶ 5d¹ 6s²ground state, subshells written in order of n
Noble gas shorthand[Xe] 5d¹ 6s²
Electrons per shell2, 8, 18, 18, 9, 2K, L, M and outward
Electrons in the outer shell2
Unpaired electrons1Hund's rule; unpaired electrons make the free atom paramagnetic
Madelung ruleBrokenthe measured ground state differs from the filling-order prediction, 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹ 5s² 5p⁶ 6s²
Quantities
Molar mass138.91 g/mol
Mass of one mole138.91 grams
Atoms in one gram4.3352824 × 10^21
Mass of one atom2.3066548 × 10^-22 g
Keep nerding
Every link below is a page Nerdulator can generate from what it already knows about this value.
Neighbouring elements
The number
Nerdulate something else
Nothing in mind? Surprise me · today’s page