Symbol	Ac
Atomic number	89
Group	3 (Scandium group)
Period	7
Block	d
Classification	Actinide

Appearance	-
Color	Silver

Number of protons	89 p+
Number of neutrons	138 n0
Number of electrons	89 e-

From Wikipedia, the free encyclopediaActinium 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.

Phase at STP	Solid
Density	10 g/cm3
Atomic weight	227 u

Melting point	1500 K 1226.85 °C 2240.33 °F
Boiling point	3500 K 3226.85 °C 5840.33 °F
Heat of vaporization	400 kJ/mol

Electronegativity (Pauling Scale)	1.1
Electron affinity	33.77 kJ/mol
Oxidation states	+3 (a strongly basic oxide)
Ionization energies	499 kJ/mol 1170 kJ/mol 1900 kJ/mol 4700 kJ/mol

Electron configuration Shorthand configuration	[Rn] 6d1 7s2
Electron configuration Full configuration	1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d10 6s2 6p6 6d1 7s2
Electron configuration chart	1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d10 6s2 6p6 6d1 7s2
Electrons per shell	2, 8, 18, 32, 18, 9, 2
Valence electrons	2
Valency electrons	3
Bohr model	Figure: Shell diagram of Actinium (Ac) atom.
Orbital Diagram 1s 2s 2p 3s 3p 3d 4s 4p 4d 4f 5s 5p 5d 6s 6p 6d 7s

Discovery	Friedrich Oskar Giesel (1902)
First isolation	Friedrich Oskar Giesel (1903)
Named by	André-Louis Debierne (1899)
Discovery of actinium André-Louis Debierne, a French chemist, announced the discovery of a new element in 1899. He separated it from pitchblende residues left by Marie and Pierre Curie after they had extracted radium. In 1899, Debierne described the substance as similar to titanium and (in 1900) as similar to thorium. Friedrich Oskar Giesel found in 1902 a substance similar to lanthanum and called it "emanium" in 1904. After a comparison of the substances' half-lives determined by Debierne, Harriet Brooks in 1904, and Otto Hahn and Otto Sackur in 1905, Debierne's chosen name for the new element was retained because it had seniority, despite the contradicting chemical properties he claimed for the element at different times. Together with polonium, radium, and radon, actinium was one of the first non-primordial radioactive elements to be isolated. The name actinium originates from the Ancient Greek aktis, aktinos (ακτίς, ακτίνος), meaning beam or ray. Its symbol Ac is also used in abbreviations of other compounds that have nothing to do with actinium, such as acetyl, acetate and sometimes acetaldehyde.

CAS Number	7440-34-8
ChemSpider ID	22404
EC number	-
PubChem CID Number	23965