Noble gas Noble gas The noble gases (historically also the inert gases; sometimes referred to as aerogens) make up a group of chemical elements with similar properties; under standard conditions, they are all odorless, colorless, monatomic gases with very low chemical reactivity. The six noble gases that occur naturally are helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and the radioactive radon (Rn). These elements are all nonmetals. Oganesson (Og) is variously predicted to be a noble gas as well or to break the trend due to relativistic effects; its chemistry has not yet been investigated. For the first six
Fluorinated gases to be phased-out globally. PFCs and SF were already in use prior to the Montreal Protocol. F-gases are ozone-friendly, very energy efficient, and safe for users and the public due to their low levels of toxicity and flammability. However, most F-gases have a relatively high global warming potential (GWP). If released, HFCs stay in the atmosphere for decades and both PFCs and SF can stay in the atmosphere for millennia. Although the Montreal Protocol regulates the phasing out of HCFCs, there was no international agreement on the regulation of HFCs until late 2016 when the Kigali Agreement under the Montreal