Monatomic gas
In physics and chemistry, monatomic is a combination of words. "Mono" means single and monatomic means single atom. It is usually applied to gases: a monatomic gas is one in which atoms are not bound to each other. Examples at standard conditions include the noble gases: helium, neon, argon, krypton, and xenon, though all chemical elements will be monatomic in the gas phase at high enough temperatures.