In physics and chemistry, monatomic is a combination of the words 'mono' and 'atomic', and means 'single atom'. It is usually applied to gases: a monatomic gas is one in which atoms are not bound to each other. All chemical elements will be monatomic in the gas phase at sufficient high temperatures. The thermodynamic behavior of monatomic gas is extremely simple when compared to polyatomic gases because it is free of any rotational or vibrational energy. In physics and chemistry, monatomic is a combination of the words 'mono' and 'atomic', and means 'single atom'. It is usually applied to gases: a monatomic gas is one in which atoms are not bound to each other. All chemical elements will be monatomic in the gas phase at sufficient high temperatures. The thermodynamic behavior of monatomic gas is extremely simple when compared to polyatomic gases because it is free of any rotational or vibrational energy.