All practice pages/Interatomic theory/Elements
Element 54, a noble gas
A heavy noble gas that proved noble gases can react, now lighting car headlights and pushing spacecraft through space.
Period 5, group 18. The other noble gases are tinted, and every cell opens its own article.
Xenon has 54 electrons, one for every proton, so the atom carries no charge. Below are the same 54 electrons written two ways.
1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁶
Short form: [Kr] 4d¹⁰ 5s² 5p⁶, where [Kr] stands for the 36 electrons krypton already has.
That list runs by shell. In the order the subshells fill it reads [Kr] 5s² 4d¹⁰ 5p⁶, 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 3 here is 3s² 3p⁶ 3d¹⁰, and 2 + 6 + 10 is 18.
Xenon sits in period 5 and has 5 shells. The period number counts the shells.
The outer shell holds 8 electrons. Those are the ones xenon can lose, gain or share, so they are the ones that decide what it bonds with. For a main-group element the group number gives that count: group 18 means 8.
A full valence shell, but its outer electrons sit far from the nucleus, so xenon can be forced to share them with fluorine and oxygen. It forms more compounds than any other noble gas.
About 0.09 parts per million of air, one of the rarest gases in the atmosphere, collected when air is liquefied and separated.
William Ramsay and Morris Travers found it in July 1898 in the residue of evaporated liquid air and named it from the Greek xenos, stranger. In 1962 Neil Bartlett made xenon hexafluoroplatinate, the first compound of a noble gas, overturning the belief that noble gases could not react.
Bright xenon lamps in car headlights, cinema projectors and camera flashes; ion thrusters on spacecraft such as NASA's Dawn probe; a general anesthetic; and large tanks of liquid xenon in underground detectors searching for dark matter.