Home > Actinium
89 Ac Actinium 227

Actinium

ACTINIDE
Bohr Model: Electrons arranged in energy shells around the nucleus.

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.

← PreviousRadium Next →Thorium

Quick Facts

Atomic Number 89
Period 7
Group 3
Phase Solid
Appearance Unknown
About Actinides

Actinides are the 15 metallic elements with atomic numbers 89–103. All actinides are radioactive.

History

Discovered By Friedrich Oskar Giesel
Named By Unknown

Physical Properties

Atomic Mass 227
Density 10 g/L
Molar Heat 27.2 J/(mol·K)
Phase Transition (Melting & Boiling Points)

Actinium melts at 1500 K and boils at 3500 K.

Atomic Properties

Electron Config [Rn] 6d1 7s2
Electronegativity 1.1
Electron Affinity 33.77 kJ/mol
Ionization Energy 499 kJ/mol
Orbital Filling Diagram
This diagram visualizes electron configuration according to the Aufbau principle and Hund's rule. Boxes represent orbitals (s, p, d, f), while arrows indicate electrons with spin up or down. Electrons fill lower energy levels first and occupy orbitals singly before pairing.

Photograph

Image of Actinium Source: Wikipedia

External Resources

Wikipedia PubChem Royal Society of Chemistry Periodic Videos (YouTube)

Study Guide

Atomic Number

The number of protons in the nucleus, which defines the element.

Atomic Mass

The average mass of an atom, including protons and neutrons.

Electronegativity

A measure of how strongly an atom attracts electrons in a bond.

Ionization Energy

The energy required to remove an electron from an atom.

Electron Config

The arrangement of electrons in the atom's energy shells.