17O resonance studies is the distinction between H2O in a complex, for example, [Co (NH3)], and solvent water.
Oxygen has two allotropes; dioxygen , O2 and trioxygen or ozone, O3. O is paramagnetric in all states and has the rather high dissociation energy of 496 kJ . Simple valence-bond theory predicts the electronic structure o-o whice, though accounting for the strong bond. Fails to account for the paramagnetism. However, simple MO theory (page 66) readily accounts for the triplet ground state having a double bond. There are several low-lying singlet states that are important in photochemical oxidations (page 302). Like NO, which has one unpaired electron in an antibonding () MO, oxygen molecules associate only weakly, and true electron pairing to form a symmetrical O4 species does not occur even in the solid. Both liquid and solid O2 are pale blue.
Ozone. The action of a silent electric discharge on O2 produces O3 in concentrations up to 10 Ozone gas is perceptibly blue and is diamagnetic. Pure ozone obtained by fractional liquefaction of O-O mixtures gives a deep blue, explosive liquid. The action of ultraviolet light on O2 produces traces of O3 in the upper atmosphere. The maximum concentration is at an altitude of 25 km. to ultraviolet light. It is of vital importance in protecting the earth’s surface from excessive exposure to ultraviolet light. Ozone is very endothermic
But it decomposes only slowly at 250 in absence of catalysts and ultraviolet light.
The O3 molecule is symmetrical and bent1.28A . Since the o-o bond distances are 1.49 A in HOOH (single bond) and 1.21 A in O2 (double bond), it is apparent that the O-O bonds in O3 must have considerable double-bond character .In terms of a reasonance description, this can be accounted for as follows
Chemical Properties of O2 and O3. Ozone is a much more powerful oxidizing agent than O2 and reacts with many substances under conditions where O2 will not. The reaction
is quantitative and can be used for analysis. Ozone is used for oxidations of organic compounds and in water purification. Oxidation mechanisms probably involve free radical chain processes as well as intermediates with --OOH groups. In acid solution, O3 is exceeded in oxidizing power only by F2 , the perxenate ion, atomic oxygen , OH radicals, and a few other such species.
The following potentials indicate the oxidizing strengths of strengths of O2 and O3 in ordinary aqueous solution