.16. (a) Derive an expression relating the mole fractions of alkali-earth oxides to the number of nonbridging oxygens per Si atom present in a silicate structure. (b) Repeat Worked Example 3.3 bor the composition Na2O0.5CaO2SiO2. Answer: 1.5 . (c) Show that chains of infinite length would occur at a mole fraction of Na2O of 0.5 , balance SiO2. What do you think the structure would be for a composition in between 0.33 and 0.5 ? (d) Show that for any silicate structure the number of nonbridging oxygens per Si is given by NBO=2R4 and the number of bridging oxygens is 82R, where R is the O/Si ratio. .16. (a) Derive an expression relating the mole fractions of alkali-earth oxides to the number of nonbridging oxygens per Si atom present in a silicate structure. (b) Repeat Worked Example 3.3 bor the composition Na2O0.5CaO2SiO2. Answer: 1.5 . (c) Show that chains of infinite length would occur at a mole fraction of Na2O of 0.5 , balance SiO2. What do you think the structure would be for a composition in between 0.33 and 0.5 ? (d) Show that for any silicate structure the number of nonbridging oxygens per Si is given by NBO=2R4 and the number of bridging oxygens is 82R, where R is the O/Si ratio