Atomic Number
57
Element 57
Lanthanum (La)
Lanthanum is a chemical element with symbol La and atomic number 57. It is a soft, ductile, silvery-white metal that tarnishes slowly when exposed to air and is soft enough to be cut with a knife.
Atomic Mass
138.91 u
Category
Lanthanide
Period
6
Group
Lanthanide series
Phase
solid
Density
6.162 g/cm3
Electron Shells
2, 8, 18, 18, 9, 2
Atomic Structure
Protons: 57. Electrons: 57. Neutrons: Varies by isotope.
Electron configuration: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 5d¹
Why Lanthanum Matters
Lanthanum helps connect atomic number 57, lanthanide behavior, period 6 trends, and electron shell structure. Its solid phase, atomic mass of 138.91 u, and electron configuration 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 5d¹ make it useful for comparing bonding patterns across the periodic table.
Discovery and Occurrence
Lanthanum was discovered 1839 by Carl Gustaf Mosander. Lanthanum is a chemical element with symbol La and atomic number 57. It is a soft, ductile, silvery-white metal that tarnishes slowly when exposed to air and is soft enough to be cut with a knife.
Safety and Handling Context
Lanthanum is presented here for learning and comparison. Pure elements and laboratory compounds can have hazards that depend on dose, form, and setting.
Related Elements
Frequently Asked Questions
- What is the atomic number of Lanthanum?
- Lanthanum has atomic number 57, which means a neutral atom has 57 protons and 57 electrons.
- What is the chemical symbol for Lanthanum?
- The chemical symbol for Lanthanum is La.
- What category is Lanthanum in?
- Lanthanum is classified as a lanthanide and sits in period 6 of the periodic table.
Explore Lanthanum in 3D
Use the interactive table above to rotate atomic models, compare periodic trends, and move from Lanthanum to neighboring elements without losing your place.