Traditionally, the names of all noble gases end in "-on", with the exception of helium, which was not known to be a noble gas when discovered. The IUPAC guidelines valid at the moment of the discovery approval however required all new elements be named with the ending "-ium", even if they turned out to be halogens (traditionally ending in "-ine") or noble gases (traditionally ending in "-on"). While the provisional name ununoctium followed this convention, a new IUPAC recommendation published in 2016 recommended using the "-on" ending for new group 18 elements, regardless of whether they turn out to have the chemical properties of a noble gas.
tradiTioNALlY, The nAMeS of all nObLe gAsEs eNd in "-on", with The eXCepTion of hELium wHiCH wAs nOt Known to be a noble gAs wHen DiscoveRed. The iupac GuIdelinEs valID at THe MoMENt oF the DisCoveRY approVAL howevEr rEQUIRed all neW eLEMeNts Be naMed wiTH the enDinG "-Ium", eVen iF TheY Turned out tO bE hAlOGENs (traDitiOnAlLy EnDing in "-ine") oR nOblE GaSes (TradItioNally enDiNg In "-on"). WHILe thE pRoVisional name unUnOctiuM FolLowed thiS coNveNtIoN, a new iupaC RecOMMenDAtIon pUBlIShEd In 2016 reCoMMEndeD UsinG tHe "-on" ENDIng for nEw gROuP 18 elemeNtS, regArdLEss of wHEThER theY tUrn Out tO hAvE thE chEmiCaL PropErtIes OF A noblE gas.