Question 3.8: Writing Formulas When Names of Compounds Are Given Write for...
Writing Formulas When Names of Compounds Are Given
Write formulas for the compounds barium oxide, calcium fluoride, and iron(III) sulfide.
Analyze
In each case, identify the cations and their charges, based on periodic table group numbers or on oxidation states appearing as Roman numerals in names: Ba^{2+}, Ca^{2+}, and Fe^{3+}. Then identify the anions and their charges: O^{2-}, F^{-}, and S^{2-}. Combine the cations and anions in the relative numbers required to produce electrically neutral formula units.
barium oxide: one {Ba}^{2+} and one {O}^{2-} = BaO
calcium fluoride: one {Ca}^{2+} and two {F}^{-} = CaF_{2}
iron(III) sulfide: two {Fe}^{3+} and three {S}^{2-} = Fe_{2}S_{3}
Assess
In the first case, an electrically neutral formula unit results from the combination of the charges 2+ and 2-; in the second case, 2+ and 2 × (1-); and in the third case, 2 × (3+) and 3 × (2-).