89 predicted 2 · 8 · 18 · 32 · 18 · 9 · 2

Actinium, Ac, element 89

Actinide· Period 7· f-block

Configuration [Rn]6d17s2

Atomic weight
227Da
Phase
solid
Density
10g/cm³
Melting point
1,323.15K, predicted 1,050 °C
Boiling point
3,473.15K, predicted 3,200 °C
Electronegativity
1.1

Silvery radioactive metallic element, belongs to group 3 of the periodic table. The most stable isotope, Ac-227, has a half-life of 217 years. Ac-228 (half-life of 6.13 hours) also occurs in nature. There are 22 other artificial isotopes, all radioactive and having very short half-lives. Chemistry similar to lanthanumpy. Used as a source of alpha particles. Discovered by A. Debierne in 1899. 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

4 of 5 fields have a value for actinium

Atomic weight The standard atomic weight. For an element with no stable isotope, the mass of its longest-lived isotope.
227Da
Source: mendeleev
Electron configuration
[Rn]6d17s2
Source: mendeleev
Electron configuration in full The electron configuration with the noble-gas core written out.
1s22s22p63s23p63d104s24p64d104f145s25p65d106s26p66d17s2
Source: Worked outfrom electron configuration
Electrons in each shell Counted from the electron configuration, from the first shell outward.
2 · 8 · 18 · 32 · 18 · 9 · 2
Source: Worked outfrom electron configuration

No data uncertainty of the atomic weight.