Randy Hughes, age 11, of Kingston, Ont., Canada, for his question:
WHY IS XENON CALLED INERT?
The word xenon means the stranger, and inert means downright lazy. Xenon is the rarest of all the gases in the air, so certainly the name stranger seems fair enough. In chemistry, the term inert means unable to combine with other elements to form molecule compounds. For a time, xenon was thought to be chemically inert‑‑but now we know that .this is not quite true.
When ordinary air is measured by volume, 78% of the gaseous mixture is nitrogen and 21% is oxygen. This leaves about 1% of the remaining space to be shared by rare gases, water vapor and various pollutants.
Six of the rare gases are classed together as a family of chemical elements. Their chemical behavior is similar because of the structure of their electron shells.
An atom's electrons are arranged in shells, somewhat like inner and outer traffic lanes. The number of electrons equals the number of protons in the nucleus. And each shell requires so many electrons to fill it.
In most elements, the outer shell is incomplete. The problem may be solved by sharing electrons with similar atoms, which then merge and form molecules of chemical compounds. This is called chemical activity. But an atom with a complete outer shell has no call to beg, borrow or swap electrons. Hence it tends to be chemically inactive, or inert.
The six rare gases in the atmosphere are helium and neon, krypton and radon, argon, which is the least rare, and xenon which is the rarest. The normal atoms of all these elements have complete outer electron shells. The single helium shell is complete with two electrons. Each of the other five has a complete outer electron shell of eight.
Most of these rare gases were discovered in the 1890s, when scientists assumed that they would not or could not combine with any other elements at all.
Then in 1962, Canadian researchers found that xenon can be coaxed to combine with a fluoride compound. Since then, other rare gases have been combined to form several chemical compounds.
Xenon is so rare that there is only about one atom among 20 million atoms and molecules in ordinary air. It can be separated as other gases are evaporated one by one from liquid air. This concentrated xenon is used in equipment for flash photography and other high‑intensity light systems. It also is used to create those miraculous light beams called lasers.