## Chemistry: The Science in Context (4th Edition)

(a) potassium bromide (KBr) (b) calcium hydride (CaH$_{2}$) (c) lithium nitride (Li$_{3}$N) (d) aluminum chloride (AlCl$_{3}$)
(a) Potassium is an alkali metal with an oxidation number of +1 whereas bromine is a halogen and has an oxidation number of -1. For a neutral compound, we need one potassium atom for every atom of bromine to keep the charge neutral. For ionic compounds, we don't need a prefix for the first element, which is a metal. For the second element (or polyatomic ion), we merely change the ending to $-ide$. The compound between potassium and bromine is potassium bromide (KBr). (b) Calcium is an alkaline earth metal with an oxidation number of +2 whereas hydrogen, with its single electron, can either act as an electron acceptor or an electron donor. In this case, hydrogen will accept an electron from calcium and take on a charge of -1. For a neutral compound, we need one calcium atom for every two atoms of hydrogen to keep the charge neutral. For ionic compounds, we don't a need a prefix for the first element, which is a metal. For the second element or polyatomic ion, which would be a nonmetal, we merely change the ending to $-ide$. The compound between calcium and hydrogen is calcium hydride (CaH$_{2}$). (c) Lithium is an alkali metal with an oxidation number of +1 whereas nitrogen, which belongs to group 15, has an oxidation number of -3. For a neutral compound, we need three lithium atoms for every atom of nitrogen to keep the charge neutral. For ionic compounds, we don't need a prefix for the first element, which is a metal. For the second element or polyatomic ion, which would be a nonmetal, we merely change the ending to $-ide$. The compound between lithium and nitrogen is lithium nitride (Li$_{3}$N). (d) Aluminum is a metal with a common oxidation number of +3 whereas chlorine, a halogen, has an oxidation number of -1. For a neutral compound, we need one aluminum atom for every three atoms of chlorine to keep the charge neutral. For ionic compounds, we don't need a prefix for the first element, which is a metal. For the second element or polyatomic ion, which would be a nonmetal, we merely change the ending to $-ide$. The compound between aluminum and chlorine is aluminum chloride (AlCl$_{3}$).