More ionic compounds
Sodium chloride is one case of a pattern. Ionic bonds generally form between a metal of low electronegativity and a non-metal of high electronegativity.
| Compound | Formula | Ions present |
|---|---|---|
| Sodium chloride | NaCl | Na+ and Cl− |
| Lithium oxide | Li2O | Li+ and O2− |
| Magnesium sulfide | MgS | Mg2+ and S2− |
| Calcium chloride | CaCl2 | Ca2+ and Cl− |
| Potassium fluoride | KF | K+ and F− |
| Copper sulfate | CuSO4 | Cu2+ and SO42− |
| Calcium carbonate | CaCO3 | Ca2+ and CO32− |
| Ammonium chloride | NH4Cl | NH4+ and Cl− |
| Ammonium nitrate | NH4NO3 | NH4+ and NO3− |
Reading the subscripts
The subscripts follow from the charges. A calcium ion carries +2 and a chloride ion −1, so two chloride ions are needed for every calcium ion, and the formula is CaCl2. Lithium is +1 and oxide −2, so lithium oxide is Li2O. Overall, an ionic compound is always electrically neutral.
The last four entries show that a polyatomic ion behaves exactly like a single one. Ammonium nitrate is built from NH4+ and NO3−, two charged groups attracting each other just as Na+ and Cl− do.
Assignment 10.1
Draw two more
Represent, in diagrams, the way ionic bonds form in lithium oxide (Li2O) and calcium chloride (CaCl2), following the way it was shown for sodium chloride. Show the electron configuration of each atom before the transfer and of each ion afterwards, and check that the charges balance.