Which of the following formulas correspond to possible...

Which of the following formulas correspond to possible nonstoichiometric oxides? $\mathrm{Ca}_{0.95} \mathrm{O}, \mathrm{Fe}_{0.95} \mathrm{O}, \mathrm{Co}_{0.95} \mathrm{O}, \mathrm{C}_{0.95} \mathrm{O}, \mathrm{Cr}_{0.95} \mathrm{O}_3$, and $\mathrm{Eu}_{0.95} \mathrm{O}$.

Key Concepts

Nonstoichiometry

Nonstoichiometry refers to compounds that deviate from the idealized fixed ratios of elements predicted by their chemical formulas. In these compounds, the proportions of elements can vary because of the presence of defects such as vacancies or interstitials in the crystal lattice, which are particularly common in certain metal oxides.

Crystal Defects

Crystal defects are disruptions in the regular atomic arrangement of a solid. In nonstoichiometric oxides, defects such as vacancies (missing atoms) or interstitials (extra atoms in normally empty spaces) allow the compound to accommodate deviations from the standard stoichiometric ratio, leading to unique physical and chemical properties.

Transition Metal Chemistry

Transition metal oxides often exhibit nonstoichiometry because the metals can exist in multiple oxidation states. This ability to change oxidation states facilitates the incorporation or removal of oxygen atoms in the lattice structure, thus enabling the formation of compounds with variable metal-to-oxygen ratios.

Stoichiometry

Stoichiometry is the branch of chemistry that deals with the numerical relationships of the elements in chemical compounds. In contrast to compounds with fixed stoichiometric ratios, nonstoichiometric materials exhibit a range of compositions that do not strictly adhere to simple whole-number ratios, often due to structural defects.

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