57La138.905
Lanthanidef-block
Lanthanum
Element 57 on the periodic table, symbol La, group 3, period 6.
Lanthanum is a soft, ductile, silvery-white metallic chemical element with symbol La and atomic number 57. It tarnishes rapidly when exposed to air and is soft enough to be cut with a knife. It gave its name to the lanthanide series, a group of 15 similar elements between lanthanum and lutetium in the periodic table: it is also sometimes considered the first element of the 6th-period transition metals.
Appearance: silvery white
Properties
- Atomic Number
- 57
- Atomic Mass
- 138.9055 u
- Group
- 3
- Period
- 6
- Block
- f-block
- Category
- Lanthanide
- State at 25 °C
- Solid
- Melting Point
- 1,193 K · 919.9 °C
- Boiling Point
- 3,737 K · 3,463.9 °C
- Density
- 6.162 g/cm³
- Atomic Radius
- 195 pm
- Electronegativity
- 1.1
- Oxidation States
- +3
- Abundance in Crust
- 39 mg/kg
- Discovered
- 1839
- Discovered By
- Carl Gustaf Mosander
Electron Configuration
[Xe] 5d16s2
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 5d1
Ionisation Energies (kJ/mol)
- 1. 538.1
- 2. 1,067
- 3. 1,850.3
- 4. 4,819
- 5. 5,940
Elements near Lanthanum
Elements in the same group share the number of outer electrons and behave in similar ways. Elements in the same period share a shell, so they change steadily from left to right.