The Ionic Bond

Ionic compounds are made up of ions or charged particles that form when an atom, or a small groups of atoms, gains or loses one or more electrons. Ionic compounds generally form when a metal reacts with a nonmetal. Each metal atom loses a certain number of its electrons and becomes a cation while the nonmetal gains the electrons lost by the metal atom and becomes and anion. When the opposite charges of cation and an anion are strongly attracted to each other , an ionic compound results. The resulting compound is electronically neutral. All ionic compounds are crystalline solids with an array of cations and anions stacked together. The faces of the crystal are where the stacks of ions come to an end. Click on ionic bonding video clip to see an animated visualization of this process.

You can predict the relative charge on a monatomic ion from the position of the parent main group elements in periodic table Transition metals often form cations with more than one relative charge and are more difficult to predict. Main group elements generally lose or gain electrons to form ions with the same number of electrons as the nearest noble gas ( Group 18 elements), so that all halogens form -1 ions while group 16 elements like oxygen and sulfur form -2 ions.

When a small group of elements bind together but form a charged species rather than a neutral compound, it is called a polyatomic ions. The bonds within the polyatomic ion are covalent but the combination of atoms does not result in a neutral compound but rather an ion is formed. The sulfate, SO42- carbonate, CO32- and nitrate, NO3 - ions are environmentally important examples of polyatomic ions. Polyatomic ions can also be involved in ionic bonds to form ionic compounds like sodium sulfate or calcium nitrate.