57 2 · 8 · 18 · 18 · 9 · 2

Lanthanum, La, element 57

Lanthanide· Period 6· f-block

Configuration [Xe]5d¹6s²

Atomic weight: 138.905Da
Phase: solid
Density: 6.15g/cm³
Melting point: 1,193.15K 920 °C
Boiling point: 3,737.15K 3,464 °C
Electronegativity: 1.1

(From the Greek word lanthanein, to line hidden) Silvery metallic element belonging to group 3 of the periodic table and oft considered to be one of the lanthanoids. Found in some rare-earth minerals. Twenty-five natural isotopes exist. La-139 which is stable, and La-138 which has a half-life of 10^10 to 10^15 years. The other twenty-three isotopes are radioactive. It resembles the lanthanoids chemically. Lanthanum has a low to moderate level of toxicity, and should be handled with care. Discovered in 1839 by C.G. Mosander. Description from mendeleev.

Back to the table

The outermost shell: the valence electronsThe inner shellsThe nucleus One bead for each electron, on the ring of its shell, counted from the nucleus out. The rings turn at their own pace; the model is Bohr's picture of the atom, which places electrons in shells but not on true orbits.

Atomic properties

5 of 5 fields have a value for lanthanum

Atomic weight The standard atomic weight. For an element with no stable isotope, the mass of its longest-lived isotope.: 138.9055Da; Source: mendeleev
Electron configuration: [Xe]5d¹6s²; Source: mendeleev
Uncertainty of the atomic weight: 7×10⁻⁵Da; Source: mendeleev
Electron configuration in full The electron configuration with the noble-gas core written out.: 1s²2s²2p⁶3s²3p⁶3d¹⁰4s²4p⁶4d¹⁰5s²5p⁶5d¹6s²; Source: Worked outfrom electron configuration
Electrons in each shell Counted from the electron configuration, from the first shell outward.: 2 · 8 · 18 · 18 · 9 · 2; Source: Worked outfrom electron configuration

Screening of each subshell

Clementi's screening constants: how much of the nucleus's charge the other electrons hide from an electron in each subshell. What is left is the effective nuclear charge it feels.

Subshell	Screening σ	Effective charge Z − σ
1s	1.1317	55.8683
2s	15.0466	41.9534
2p	4.2044	52.7956
3s	19.0569	37.9431
3p	18.8604	38.1396
3d	13.9398	43.0602
4s	28.2036	28.7964
4p	29.2936	27.7064
4d	32.2748	24.7252
4f	55.64	1.36
5s	39.189	17.811
5p	41.104	15.896
6s	47.688	9.312