Introduction to Ionic Compounds

Many ions have a noble gas configuration Ions with a noble gas configuration are stable.

A sodium atom has only one electron in its outer shell. Losing this electron produces an ion, Na +, with a noble gas configuration.

A chlorine atom has 7 electrons in its outer shell. Adding one electron produces an ion, Cl -, with a noble gas configuration.

Isoelectronic ions have the same electron configuration. Many ions are isoelectronic with the noble gases. Many ions are isoelectronic with the noble gases. These are the atoms found in the s and p blocks. These are the atoms found in the s and p blocks. They follow the octet rule. They follow the octet rule.

Transition metals Transition metals do not form ions that are isoelectronic with noble gases. Transition metals do not form ions that are isoelectronic with noble gases. These metals often use d-orbital electrons in their bonding. These metals often use d-orbital electrons in their bonding. Some transition metals can form more than one cation. Some transition metals can form more than one cation. e.g. Copper can form two ions, Cu + and Cu 2+. e.g. Copper can form two ions, Cu + and Cu 2+. Iron can form two ions, Fe 2+ and Fe 3+. Iron can form two ions, Fe 2+ and Fe 3+.

Ionic substances form crystals held together by ionic bonds. Notice that each ion is surrounded by ions of the opposite charge. Notice that each ion is surrounded by ions of the opposite charge. The ions are arranged such that the coulombic force of attraction is significantly greater than the force of repulsion. The ions are arranged such that the coulombic force of attraction is significantly greater than the force of repulsion.

Formulas for Ionic Compounds THERE IS NO SUCH THING AS AN IONIC MOLECULE. THERE IS NO SUCH THING AS AN IONIC MOLECULE. Instead, formula units for ionic compounds are the simplest ratio of the ions. Instead, formula units for ionic compounds are the simplest ratio of the ions. e.g. The formula unit for sodium chloride is NaCl because there is one Na + ion for every Cl - ion.

Not all ionic compounds have the same structure. Note that each sodium ion is surrounded by 6 chlorine atoms, but each cesium atom is surrounded by 8 chlorine atoms. This structure is dictated by the relative size of the atoms.

Lattice energy is the key to ionic bond formation. Lattice energy is the energy released when ions (or atoms or molecules) come together to form a crystal. Lattice energy is the energy released when ions (or atoms or molecules) come together to form a crystal. The energy released is far greater than the energy required in the endothermic steps of separating molecules, converting them to a gaseous state, and ionization. The energy released is far greater than the energy required in the endothermic steps of separating molecules, converting them to a gaseous state, and ionization. Energy is also released by gaining electrons, but not enough to drive the process. Energy is also released by gaining electrons, but not enough to drive the process.

Properties of Ionic Compounds Ionic crystals are hard and brittle. Ionic crystals are hard and brittle. Because of their repeating crystalline pattern, they cleave along planes. Because of their repeating crystalline pattern, they cleave along planes. Ionic compounds melt and boil at high temperatures. Ionic compounds melt and boil at high temperatures. Ionic solids do not conduct electricity, but liquid ionic compounds and solutions of ionic compounds do. Ionic solids do not conduct electricity, but liquid ionic compounds and solutions of ionic compounds do.

Compare the orderly crystal arrangement of solid NaCl to molten and dissolved NaCl. Ions in a solid are packed tightly and cannot move to conduct electricity. Ions in a solid are packed tightly and cannot move to conduct electricity. Molten or dissolved ions are free to move and thus conduct electricity. Molten or dissolved ions are free to move and thus conduct electricity.