Chlorine oxides thumb|right|Yellow chlorine dioxide (ClO2) gas above a solution of hydrochloric acid and sodium chlorite in water, also containing dissolved chlorine dioxide thumb|right|Structure of dichlorine heptoxide, Cl2O7, the most stable of the chlorine oxides The chlorine oxides are well-studied in spite of their instability (all of them are endothermic compounds). They are important because they are produced when chlorofluorocarbons undergo photolysis in the upper atmosphere and cause the destruction of the ozone layer. None of them can be made from directly reacting the elements.
ChLOrine oxiDEs thuMb|Right|yeLlOW CHlOrinE DioxIde (cLO2) gas AbOve A SolUTiOn of HyDrochlorIc ACId And sodium cHLoRite iN wateR, ALSo contaiNing dISSolvED cHlOrine diOxidE THuMb|right|StRuctUre oF dIChLOrinE HeptoxIde, CL2o7, The mOsT StaBlE of ThE chLoRine oxides the ChLORIne oxidEs are WEll-sTuDiEd In sPite Of their InstabilIty (alL of THeM are endothErMic compoUnds). They arE important bEcaUse They aRe prodUceD WhEn chlOrofluOrocaRbons undergo PHotolysis In the UppeR ATMOSPhEre and cAuse the dEstruCtiOn Of thE ozoNE lAyer. noNe of thEm caN Be maDE from diReCTLy rEacTiNg the eleMENTs.