Ac

Actinium · element 89

Actinide · Solid at room temperature

Actinium is a radioactive chemical element with symbol Ac (not to be confused with the abbreviation for an acetyl group) and atomic number 89, which was discovered in 1899. It was the first non-primordial radioactive element to be isolated. Polonium, radium and radon were observed before actinium, but they were not isolated until 1902.

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Actinium-225 medical radioisotope held in a v-vial at ORNL. The blue glow comes from the ionization of surrounding air by alpha particles
Actinium-225 medical radioisotope held in a v-vial at ORNL. The blue glow comes from the ionization of surrounding air by alpha particles - Oak Ridge National Laboratory, CC BY 2.0 <https://creativecommons.org/licenses/by/2.0>, via Wikimedia Commons, source: https://www.flickr.com/photos/oakridgelab/31481701837/

Key facts

Atomic mass
227 u
how heavy one atom is
Phase (room temp.)
Solid
Density
10 g/cm³
how tightly packed it is
Melting point
1500 K (1227 °C)
when solid turns to liquid
Boiling point
3500 K (3227 °C)
when liquid turns to gas
Period
7
its row in the periodic table
Group
3
its column in the periodic table
Block
F-block
the neighbourhood it lives in
Electronegativity
1.1
how strongly it pulls electrons
Electron configuration
[Rn] 6d1 7s2
where its electrons live
Shells
2 · 8 · 18 · 32 · 18 · 9 · 2
electrons in each layer, inside to out
Discovered by
Friedrich Oskar Giesel
who found it

Source: Wikipedia

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