089Actinide · Group 3 · Period 7

Actinium

Actinium (Ac) is element 89, a actinide in the f-block — group 3, period 7. It is a solid at room temperature with 7 electron shells (2, 8, 18, 32, 18, 9, 2) and an atomic mass of 227 u.

Atomic mass: 227.0 u
Phase · STP: solid
Melting: 1500 K · 1227 °C
Boiling: 3500 K · 3227 °C
Electronegativity: 1.1
Density: 10 g/cm³

Photograph — 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/

Identity

Atomic number: 89
Standard atomic weight: 227.0 u
Category: Actinide
Group: 3
Period: 7
Block: f-block
Oxidation states: +3

Physical properties

Melting point: 1500 K · 1227 °C
Boiling point: 3500 K · 3227 °C
Density: 10 g/cm³
Molar heat capacity: 27.2 J/(mol·K)
Atomic radius: 260 pm
Electron affinity: 33.77 kJ/mol

Atomic structure

89protons

138neutrons

89electrons

2valence e⁻

Noble-gas notation: [Rn] 6d1 7s2
Full configuration: 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2 6d1
Electrons per shell: 2, 8, 18, 32, 18, 9, 2

Periodic trends

Where Actinium ranks across all 118 elements.

Electronegativity1.1

Ionization energy499 kJ/mol

Electron affinity33.77 kJ/mol

Density10 g/cm³

Atomic radius260 pm

Ionization energies

Energy to remove each successive electron (kJ/mol).

499

1.2k

Successive ionization energies (kJ/mol, log scale).

Discovery

Discovered: 1899
Discovered by: Friedrich Oskar Giesel
Named by: —
Appearance: —