All practice pages/Interatomic theory/Elements
Element 95, an actinide
Made during World War II, first revealed on a children's radio quiz show, and now sitting in millions of smoke detectors.
Period 7, in the actinide row set below the main table. The other actinides are tinted, and every cell opens its own article.
Americium has 95 electrons, one for every proton, so the atom carries no charge. Below are the same 95 electrons written two ways.
1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 5f⁷ 6s² 6p⁶ 7s²
Short form: [Rn] 5f⁷ 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 5f⁷, 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.
Americium sits in period 7 and has 7 shells. The period number counts the shells.
The outer shell holds 2 electrons. Those are the ones americium 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.
Not found in nature. It is made in nuclear reactors from plutonium.
Glenn Seaborg, Ralph James, Leon Morgan and Albert Ghiorso made it in 1944 at the University of Chicago's wartime Metallurgical Laboratory. Seaborg first revealed it on the children's radio show Quiz Kids in November 1945, days before the official announcement. It was named after the Americas, just as europium above it had been named after Europe.
Ionization smoke detectors hold a fraction of a microgram of americium-241, whose alpha particles let a tiny current flow until smoke interrupts it. Americium-beryllium neutron sources measure moisture in soil and probe the rock around oil wells.
Radioactive. The source in a smoke detector is safe while sealed, but it should never be taken out or broken open.