Introduction to Ionic Introduction to Ionic CompoundsCompounds

Many ions have a noble gas Many ions have a noble gas configurationconfiguration

Ions with a noble gas configuration are stable.

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

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

Isoelectronic ions have the Isoelectronic ions have the same electron configuration.same electron configuration.

Many ions are isoelectronic with the Many ions are isoelectronic with the noble gases. noble gases. These are the atoms found in the These are the atoms found in the ss and and pp blocks. blocks.

They follow the octet rule.They follow the octet rule.

Transition metals Transition metals

Transition metals do not form ions that are Transition metals do not form ions that are isoelectronic with noble gases.isoelectronic with noble gases.

These metals often use These metals often use dd-orbital electrons -orbital electrons in their bonding.in their bonding.

Some transition metals can form more Some transition metals can form more than one cation.than one cation. e.g. Copper can form two ions, Cue.g. Copper can form two ions, Cu++ and Cu and Cu2+2+.. Iron can form two ions, FeIron can form two ions, Fe2+2+ and Fe and Fe3+3+..

Ionic substances form crystals Ionic substances form crystals held together by ionic bonds.held together by ionic bonds.

Notice that each ion Notice that each ion is surrounded by is surrounded by ions of the opposite ions of the opposite charge.charge.

The ions are The ions are arranged such that arranged such that the coulombic force the coulombic force of attraction is of attraction is significantly greater significantly greater than the force of than the force of repulsion.repulsion.

Formulas for Ionic Formulas for Ionic CompoundsCompounds

THERE IS NO SUCH THERE IS NO SUCH THING AS AN IONIC THING AS AN IONIC MOLECULE.MOLECULE.

Instead, formula units Instead, formula units for ionic compounds for ionic compounds are the simplest ratio are the simplest ratio of the ions.of the ions. e.g. The formula unit for e.g. The formula unit for

sodium chloride is NaCl sodium chloride is NaCl because there is one because there is one NaNa++ ion for every Cl ion for every Cl-- ion. ion.

Not all ionic compounds have the Not all ionic compounds have the same structure.same structure.

Note that each sodium ion is surrounded by 6 chlorine Note that each sodium ion is surrounded by 6 chlorine atoms, but each cesium atom is surrounded by 8 atoms, but each cesium atom is surrounded by 8 chlorine atoms.chlorine atoms.

This structure is dictated by the relative size of the atoms.This structure is dictated by the relative size of the atoms.

Lattice energy is the key to ionic bond Lattice energy is the key to ionic bond formation.formation.

Lattice energy is the energy Lattice energy is the energy released when ions (or released when ions (or atoms or molecules) come atoms or molecules) come together to form a crystal.together to form a crystal.

The energy released is far The energy released is far greater than the energy greater than the energy required in the endothermic required in the endothermic steps of separating steps of separating molecules, converting them molecules, converting them to a gaseous state, and to a gaseous state, and ionization.ionization.

Energy is also released by Energy is also released by gaining electrons, but not gaining electrons, but not enough to drive the enough to drive the process.process.

Properties of Ionic Properties of Ionic CompoundsCompounds

Ionic crystals are hard and brittle.Ionic crystals are hard and brittle. Because of their repeating crystalline Because of their repeating crystalline

pattern, they cleave along planes.pattern, they cleave along planes. Ionic compounds melt and boil at Ionic compounds melt and boil at

high temperatures.high temperatures. Ionic solids do not conduct Ionic solids do not conduct

electricity, but liquid ionic electricity, but liquid ionic compounds and solutions of ionic compounds and solutions of ionic compounds do.compounds do.

Compare the orderly crystal Compare the orderly crystal arrangement of solid NaCl to molten arrangement of solid NaCl to molten and dissolved NaCl.and dissolved NaCl.

Ions in a solid are Ions in a solid are packed tightly and packed tightly and cannot move to cannot move to conduct electricity.conduct electricity.

Molten or dissolved Molten or dissolved ions are free to ions are free to move and thus move and thus conduct electricity.conduct electricity.