Yes. Actinium is a metal, classified as an actinide on the periodic table.

How many protons does actinium have?

Actinium has 89 protons. Its atomic number is 89, which is also the number of electrons in a neutral atom of actinium.

What group and period is actinium in?

Actinium is in period 7 of the periodic table. As an actinide in the f-block, it sits in a separate row below the main table and has no standard group number.

What is the atomic mass of actinium?

The atomic mass of actinium is 227 u (unified atomic mass units).

Element 89

Actinium (Ac)

Actinide · Period 7 · f-block

Actinium (Ac) is element 89 of the periodic table, an actinide in period 7 (f-block) with an atomic mass of 227 and is a solid at standard conditions.

At a glance

Atomic number: 89
Symbol: Ac
Atomic mass: 227 u
Category: Actinides
Period: 7
Block: f-block
Phase at STP: solid

Electron structure

Electron configuration: 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d10 6s2 6p6 6d1 7s2
Shorthand configuration: [Rn] 6d1 7s2
Electrons per shell: 2, 8, 18, 32, 18, 9, 2
Oxidation states: +2, +3

Physical properties

Melting point: 1,323 K (1,049.85 °C)
Boiling point: 3,471 K (3,197.85 °C)
Density: 10.07 g/cm³
Phase: solid

Atomic properties

Electronegativity (Pauling): 1.1
Atomic radius: 195 pm
Covalent radius: 215 pm
First ionization energy: 499 kJ/mol
Electron affinity: 33 kJ/mol

Notable isotopes

Notable isotopes of Actinium: mass number, atomic mass, natural abundance, and stability.
Isotope	Mass	Abundance	Stability
Ac-227	227.02775	-	Half-life 21.8 years

Common uses

Neutron source
Cancer treatment research
Thermoelectric generators

Discovery

Year: 1899
Discovered by: André-Louis Debierne
Country: France

Frequently asked questions

Is actinium a metal?: Yes. Actinium is a metal, classified as an actinide on the periodic table.
How many protons does actinium have?: Actinium has 89 protons. Its atomic number is 89, which is also the number of electrons in a neutral atom of actinium.
What group and period is actinium in?: Actinium is in period 7 of the periodic table. As an actinide in the f-block, it sits in a separate row below the main table and has no standard group number.
What is the atomic mass of actinium?: The atomic mass of actinium is 227 u (unified atomic mass units).

Keep exploring

Actinium's row is on the printable element property sheet, and its tile is on the periodic table wall chart - the same numbers as above, laid out for A4 or A3 paper.