Chapter 5 - Molecules and Compounds - Exercises - Problems - Page 158: 53

a) $Na_{2}S$ b) $SrO$ c) $Al_{2}S_{3}$ d) $MgCl_{2}$

An ionic compound is a special type of compound in chemistry where ions are held together by electrostatic forces (i.e. ionic bonds). Ionic compounds consists of a cation and an anion. a) Sodium Sulfide ($Na_{2}S)$ is an ionic compound made of sodium and sulfur. Since Na forms $Na^{+}$ and S forms $S^{2-}$, combing the two by crossing down the charges gives us ($Na_{2}S)$. b) Strontium Oxide ($SrO)$ is an ionic compound made of strontium and oxygen. Since O forms $O^{2-}$ and Sr forms $S^{2-}$, combining the two gives us ($SrO)$. c) Aluminum Sulfide ($Al_{2}S_{3})$ is an ionic compound made of aluminum and sulfur. Since Al forms $Al^{3+}$ and S forms $S^{2-}$, combing the two and crossing down the charges gives us ($Al_{2}S_{3})$ d) Magnesium Chloride ($MgCl_{2})$ is an ionic compound made of aluminum and sulfur. Since Mg forms $Mg^{2+}$ and Cl forms $Cl^{-}$, combining the two and crossing down the charges gives us ($MgCl_{2})$