Actinium (Ac)

Actinium is a chemical element with symbol Ac and atomic number 89. It is the first element of the actinide series. Actinium gave the name to the actinide series, a group of 15 similar elements between actinium and lawrencium in the periodic table.

Atomic Number

89

Atomic Mass

227 u

Category

actinide

Phase

solid

Density

10.07 g/cm³

Electron Shells

2, 8, 18, 32, 18, 9, 2

Atomic Structure

Protons: 89 • Electrons: 89 • Neutrons: Varies by isotope

Electron Configuration: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰ 6p⁶ 7s² 6d¹

Discovery

1899 • André-Louis Debierne