57La138.91
Lanthanum (La)
Element 57 · Lanthanide
Lanthanum (La) is a chemical element with atomic number 57. It is classified as a lanthanide in period 6 of the periodic table (the f-block). Its standard atomic weight is 138.91 u and its ground-state electron configuration is [Xe] 5d¹ 6s².
Lanthanum facts
| Atomic number (Z) | 57 |
|---|---|
| Symbol | La |
| Standard atomic weight | 138.91 u |
| Category | Lanthanide |
| Group | — (f-block) |
| Period | 6 |
| Block | f-block |
| Electron configuration | [Xe] 5d¹ 6s² |
| Electronegativity (Pauling) | 1.1 |
| State at 20 °C | Solid |
| Protons / electrons | 57 / 57 |
| Neutrons (most common isotope, approx.) | 82 |
| Molar mass | 138.91 g/mol |