Suppose that CaO is added as an impurity to Li2O. If the Ca2+ substitutes for Li+, what kind of vacancies would you expect to form? How many of these vacancies are created for every Ca2+ added? (b) Suppose that CaO is added as an impurity to CaCl2. If the O2– substitutes for Cl–, what kind of vacancies would you expect to form? How many of these vacancies are created for every O2– added?

(a) When Li+ is substituted for Ca2+ in CaO, there would be oxygen vacancies created because for each Li+ that is substituted for Ca2+, a positive charge is removed (vacant). Therefore, to maintain neutrality, a negative charge must be removed. This occurs by creating oxygen vacancies. That is, for every two Li+ ions added, one oxygen vacancy is created.

(b) When Cl- is substituted by O2- in CaO, there are now calcium vacancies, .because each Cl- substituted by O2-, implies that one negative charge has been removed(vacant). Therefore, to maintain neutrality, when two Cl- ions are substituted by O2- ion, one calcium vacancy calcium vacancy is created.