Group 16 elements form EO2- and EO3-type oxides (E = S, Se, Te, Po) that are acidic, reacting with water to form the corresponding oxoacid (SO2+H2O -> H2SO3; SeO3+H2O -> H2SeO4); reducing power of the dioxides falls from SO2 (reducing) to TeO2 (oxidising). Group 17 elements form many, mostly unstable oxides: fluorine's OF2/O2F2 are strong fluorinating agents; chlorine's Cl2O/ClO2/Cl2O6/Cl2O7 are explosive oxidisers (ClO2 used for bleaching/water treatment); bromine's oxides are the LEAST stable of any halogen's (the 'middle row anomaly'); iodine's I2O5 is used to estimate carbon monoxide. Group 18 is inert to oxygen directly. Towards halogens, group 16 forms EX6 (octahedral, sp3d2, e.g. SF6), EX4 (see-saw, sp3d, e.g. SF4) and EX2 (bent, sp3, e.g. SCl2) halides, plus dimeric monohalides that disproportionate; stability falls fluoride > chloride > bromide > iodide. Group 17 elements combine with each other to form interhalogen compounds (detailed separately). Group 18 is generally inert to halogens too, except that xenon (and, far more weakly, krypton) reacts directly with fluorine to give the xenon fluorides. Towards metals, group 16 forms chalcogenides (Cu+S -> CuS), group 17 forms halides essentially instantly (ionic character MF>MCl>MBr>MI), and group 18 does not react with metals at all.