Spinels are solids with the general formula M²⁺(M′³⁺)₂O₄ (where M²⁺ and M′³⁺ are metal cations of the same or different metals). The bestknown example is common magnetite, Fe₃O₄ [which you can formulate as (Fe²⁺)(Fe³⁺)₂O₄].

(a) Given its name, it is evident that magnetite is ferromagnetic. How many unpaired electrons are in iron(II) and in iron(III) ions?

(b) Two other spinels are CoAl₂O₄ and SnCo₂O₄. What metal ions are involved in each? What are their electron configurations? Are the metal ions paramagnetic, and if so, how many unpaired electrons are involved?

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A crystal of a spinel Ⓒ Cengage Learning/Charles D. Winters