Ionic Compounds

Why Care About Ionic Compounds?





The reason ionic compounds are important might not be obvious you. The first time you see them, is usually in general chemistry. Yet no one explains what they do.



As a result, ionic compounds end up as the poor cousin to molecular compounds. This creates the impression they are obscure. In particular, this article will try to point out otherwise.



Ionic Compounds Form From Metals and Nonmetals





Basic Composition




Metal and nonmetal region of periodic table. Metals give up electrons, nonmetals accept electrons
Figure 1: Metal cations and nonmetal anions form ionic compounds.

It must be remembered, ionic compounds form when a metal atom reacts with a nonmetal. Metal atoms donate electrons to a nonmetal. When a metal gives up electrons it becomes a cation. At the same time, a nonmetal absorbs electrons it adopts a negative charge to become an anion, Figure 1.





cations lose electrons and anions gain electrons
Figure 2: Metals lose electrons while nonmetals gain electrons

Electrons flow from metals to nonmetals. This provides a way to predict which combination of elements form ionic compounds.


In Figure 2, both metal and nonmetal start as neutral until the encounter each other. The metal loses electrons. At the same time, a nonmetal element gains electrons.




Polyatomic Ions




selected polyatomic ions
Figure 3: A short list of polyatomic ions

In addition, not only individual atoms form charges. Groups and clusters of atoms can act as a single unit. Therefore the entire cluster possess an overall charge.



The most common clusters form anions. Treat clusters the same way you treat a single nonmetal anion.




Figure 3 shows a short list of common polyatomic ions. Each consists of a nonmetal element and three or four oxygens. These polyatomic ions find use as structural materials for building.




Earth’s Crust Made of Ionic Compounds




molecular silicate structure
Figure 4 : Tetrahedral structure of silicate anion

For example, silicate minerals make up ninety percent of the earth’s crust. Silicates have a base unit composed of [SiO4]-4, Figure 4.



Silicon sits at the center of the four oxygens. They form a tetrahedron. The silicate tetrahedron combines to build a wide assortment of minerals.









Likewise, other polyatomic ions form large deposits of minerals. One well known type is calcite, CaCO3, known as chalk. The white cliffs of Dover are made of calcite.




Furthermore, industrial minerals are composed of metal oxides, metal sulfides, and metal halides. Each one of these will be explained.




Metallurgy Starts with Ionic Compounds




Significantly, the majority of metals exist as metal oxides or metal sulfides. On the whole, extraction of metals from minerals occurs from smelting or roasting









simple blast furnace diagram
Figure 5: Schematic picture of blast furnace shows how ionic iron oxide reacts with carbon to purify iron

For example, Iron oxide in the form of hematite, Fe2O3, occupies the role of the most important metal. Smelting takes place in a blast furnace. The metal reacts at high temperature with carbon. This produces purified metal and carbon dioxide, Figure 5.



Raw material feeds into the blast furnace. It consists of hematite, (Fe2O3), coke, (activated carbon), and limestone, (CaCO3).







Heated air “blasts” into the furnace. Under these conditions, carbon reacts with oxygen to form CO. Meanwhile, carbon monoxide reacts with iron (III) oxide. This causes iron metal and CO2 to form as products, Equation (1).



\bold{\Large{2\;Fe_2O_3 + 3\;CO \longrightarrow 2\;Fe + 3\; CO_2}} (1)






Equally important, other important metals occur as their metal sulfides. To prepare them for smelting, they undergo conversion to metal oxides. Most notable among these minerals are: Cu2S, (chalcocite) and ZnS, (sphalerite). The sulfides combust in air and result in metal oxide with the extrusion of SO2, Equations (2) and (3).



\bold{\Large{2\;Cu_2S + 3\;O_2 \longrightarrow 2\;Cu_2O + 2\; SO_2}} (2)




\bold{\Large{2\;ZnS + 3\;O_2 \longrightarrow 2\;ZnO + 2\; SO_2}}  (3)





Ceramics From Ionic Compounds




clay made of alternating layers of tetrahedral silicates and octahedral aluminates in sheets separated by water and cation layers
Figure 6: Clay composed of ionic silicate and aluminate with water and cations between sheets

Furthermore, ceramics occupy the other most important class of common building materials.



Of course, technically, all ionic compounds are ceramics. Albeit, in everyday English, “ceramics” means things made from  clay. In general, these materials consist of sheets of silicates and aluminates. Sheets separate with layers of water. Then the water layer can host cations.


After that, the raw material gets fired in an oven. Heat drives the water out. As a result, the ceramic becomes hard.