All practice pages/Interatomic theory/Elements
Element 89, an actinide
The first of the actinides, the row it names, and so radioactive that it glows pale blue in the dark.
Period 7, in the actinide row set below the main table. The other actinides are tinted, and every cell opens its own article.
Actinium has 89 electrons, one for every proton, so the atom carries no charge. Below are the same 89 electrons written two ways.
1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 6s² 6p⁶ 6d¹ 7s²
Short form: [Rn] 6d¹ 7s², where [Rn] stands for the 86 electrons radon already has.
That list runs by shell. In the order the subshells fill it reads [Rn] 7s² 6d¹, because a subshell fills by its energy, not by its shell number.
The simple form counts electrons shell by shell. The orbital form says which subshell each one sits in: s holds 2, p holds 6, d holds 10 and f holds 14. Shell 4 here is 4s² 4p⁶ 4d¹⁰ 4f¹⁴, and 2 + 6 + 10 + 14 is 32.
Actinium sits in period 7 and has 7 shells. The period number counts the shells.
The outer shell holds 2 electrons. Those are the ones actinium can lose, gain or share, so they are the ones that decide what it bonds with.
Radioactive, like every actinide. It gives up electrons to form positive ions.
Present in uranium ores in tiny traces. Most is made by bombarding radium with neutrons in reactors.
André-Louis Debierne reported it in 1899 in residues from pitchblende, and Friedrich Oskar Giesel found it independently in 1902. The name comes from the Greek aktis, ray.
Actinium-225 is being developed for targeted alpha therapy against cancer, and mixtures of actinium and beryllium have served as neutron sources.
Intensely radioactive, handled only in specialized facilities.