Noble gas periods of the periodic table, the noble gases are exactly the members of group 18. Noble gases are typically highly unreactive except when under particular extreme conditions. The inertness of noble gases makes them very suitable in applications where reactions are not wanted. For example, argon is used in incandescent lamps to prevent the hot tungsten filament from oxidizing; also, helium is used in breathing gas by deep-sea divers to prevent oxygen, nitrogen and carbon dioxide (hypercapnia) toxicity. The properties of the noble gases can be well explained by modern theories of atomic structure: their outer shell of valence electrons
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