Problem 12 - Chemical Principles: The Quest for Insight

Question

Write formulas for the ionic compounds formed from (a) calcium and chloride ions; (b) iron(III) and sulfate ions; (c) ammonium and iodide ions; (d) lithium and sulfide ions; (e) calcium and phosphide ions.

Step-by-Step Solution

Answer

The ionic compounds are: (a) CaCl2, (b) Fe2(SO4)3, (c) NH4I, (d) Li2S, (e) Ca3P2.

Step 1: Determine the ions and their charges

Identify the ions of each element and their oxidation states. Calcium (Ca) typically has a charge of +2. Chloride (Cl) has a charge of -1. Iron(III) (Fe) has a charge of +3. Sulfate ((SO_4)^{2-}) has a charge of -2. Ammonium ((NH_4)^{+}) has a charge of +1. Iodide (I) has a charge of -1. Lithium (Li) has a charge of +1. Sulfide (S) has a charge of -2. Calcium (Ca) again has a charge of +2, and phosphide (P) has a charge of -3.

Step 2: Combine the ions in ratios that balance their charges

Combine the ions in a ratio so the total charge is neutral. (a) Ca(2+) and Cl(-) form CaCl2 because two chloride ions are needed to balance one calcium ion. (b) Fe(3+) and SO4(2-) form Fe2(SO4)3 because two iron(III) ions are needed to balance three sulfate ions. (c) NH4(+) and I(-) simply combine in a one to one ratio to form NH4I. (d) Li(+) and S(2-) combine in a two to one ratio to form Li2S. (e) Ca(2+) and P(3-) combine in a three to two ratio to form Ca3P2.

Key Concepts

Chemical Bonding

Understanding the basics of chemical bonding is essential to grasp how ionic compounds are formed. Chemical bonding refers to the way that atoms attach to one another to form molecules and compounds. There are several types of chemical bonds, including ionic bonds, covalent bonds, and metallic bonds, but here, we are focusing on ionic bonding.