What Is Lanthanum?
Lanthanum is a chemical element with the symbol La and atomic number 57, part of the lanthanide series of rare earth elements.
The first lanthanide. A soft, silvery-white metal used in camera lenses and EV batteries.
As a lanthanide in Period 6 and Group 3 (Transition Metals), lanthanum's placement on the table reflects its electron configuration of [Xe] 5d¹ 6s², which governs its bonding behavior and the type of compounds it typically forms.
Position on the Periodic Table
Lanthanum is located in Period 6, an unusually long row that includes the entire lanthanide series.
Within that row, lanthanum sits in Group 3 (Transition Metals), alongside elements that share a similar number of valence electrons and, by extension, similar chemical behavior.
This position is not arbitrary — the periodic table was deliberately organized so that an element's row and column reveal its expected reactivity, bonding pattern, and physical state at a glance.
Physical & Chemical Properties
Lanthanum has an atomic mass of 138.905 u and a density of 6.162 g/cm³. Its melting point is 918°C and its boiling point is 3464°C.
Lanthanum displays the typical lanthanide combination of a silvery appearance and chemistry dominated by its f-orbital electrons.
Electron Configuration Explained
Lanthanum's electron configuration is [Xe] 5d¹ 6s², describing how its electrons are distributed across shells and subshells around the nucleus.
Reading the configuration in order shows electrons filling shells of increasing energy, following the standard Aufbau principle that explains how atomic structure builds up across the periodic table.
The outermost (valence) electrons shown in this configuration are what ultimately determine lanthanum's chemical reactivity and the type of bonds it forms with other elements.
History & Discovery
Lanthanum was formally discovered in 1839, C.G. Mosander, identified through the careful isolation and analytical techniques typical of that era's chemical research.
Many elements from this period were anticipated by Dmitri Mendeleev's periodic table, which successfully predicted gaps corresponding to undiscovered elements well before laboratory instruments existed to confirm them directly.
What Is Lanthanum Used For?
Lanthanum's specific properties make it useful in several applications, including:
- Camera lenses
- Hydrogen storage
- Electric car batteries
- Petroleum refining
- Studio lighting
These uses reflect lanthanum's underlying classification as a lanthanide, since the same properties that define its category in chemistry also determine where it becomes practically useful.
Fun Facts About Lanthanum
- A typical Prius battery has about 10–15 kg of lanthanum.
- Lanthanum is element number 57 on the periodic table, in Period 6 and Group 3.
- Its standard atomic mass is 138.905 u, calculated from the natural abundance of its isotopes.
Frequently Asked Questions
What is Lanthanum's atomic number?
Lanthanum has atomic number 57.
What is Lanthanum's chemical symbol?
Lanthanum's symbol is La.
What group and period is Lanthanum in?
Lanthanum is in Period 6, Group 3 (Transition Metals).
What is Lanthanum's atomic mass?
Lanthanum's standard atomic mass is 138.905 u.