3.5 Ionic Compounds
3.5 Ionic Compounds
- Describe ionic compounds and how they form.
- Explain how ionic compounds are named.
- Identify properties and uses of ionic compounds.
The truck pictured above is spreading crystals of the salt calcium chloride on a snowy road to prevent ice from
forming. The crystals lower the freezing point of water so when the snow melts, it won’t turn to ice. Do you know
why calcium chloride lowers the freezing point of water? The answer has to do with the type of compound that
calcium chloride is. Calcium chloride is an ionic compound.
What Are Ionic Compounds?
All compounds form when atoms of different elements share or transfer electrons. Compounds in which electrons
are transferred from one atom to another are called ioniccompounds. In this type of compound, electrons actually
move between the atoms, rather than being shared between them. When atoms give up or accept electrons in this
way, they become charged particles called ions. The ions are held together by ionic bonds, which form an ionic
compound. Ionic compounds generally form between elements that are metals and elements that are nonmetals. For
example, the metal calcium (Ca) and the nonmetal chlorine (Cl) form the ionic compound calcium chloride (CaCl 2 ).
In this compound, there are two negative chloride ions for each positive calcium ion. Because the positive and
negative charges cancel out, an ionic compound is neutral in charge.
Q:Now can you explain why calcium chloride prevents ice from forming on a snowy road?
A:If calcium chloride dissolves in water, it breaks down into its ions (Ca^2 +and Cl−). When water has ions dissolved
in it, it has a lower freezing point. Pure water freezes at 0°C. With calcium and chloride ions dissolved in it, it won’t
freeze unless the temperature reaches -29°C or lower.