8.2: The formation and nature of ionic bonds

Objectives Describe the formation of ionic bonds Account for many of the physical properties of an ionic compound Discuss the energy involved in the formation of an ionic bond

Key Terms Ionic bond Electrolyte Lattice energy

Formation of Ionic Bonds One atom transfers its electrons to another atom These two atoms are then held together by the electrostatic (magnetic) attraction Example: NaCl

Formation of Ionic Bonds Compound formed is ‘electronically neutral’ Net + charge = Net - charge Example: Na+ would need 1 Cl-

Example 1 Al3+ and Cl- ions

Example 2 Li+ and O2-

Example 3 Fe3+ and O2-

ANSWER: 2 Fe3+ AND 3 O2-

Formation of Ionic Bonds Na+ Cl- Properties of Ionic Compounds In an ionic compound the positive and negative parts are arranged so minimize repulsion. This arrangement is called a crystal lattice.

Properties of Ionic Compounds Hard brittle solids High boiling points _________ melting points _________conductors of heat and/or electricity These properties are all related to the crystal lattice and strength of bond

Properties of Ionic Compounds Melting and boiling point Recall that the solids are rigidly arranged, liquids more loosely arranged, and gases most loosely arranged. (picture on next slide)

Properties of Ionic Compounds

Properties of Ionic Compounds Also recall melting point is the temperature that a solid becomes a liquid and boiling point is the temperature that a liquid becomes a gas. So for particles to get further away from each other (solid to liquid or liquid to gas) enough energy (temperature) must be supplied to break (or loosen) the strong ionic bonds between particles.

Properties of Ionic Compounds Ionic compounds are hard brittle solids Recall the picture of the crystal lattice. What if you moved one of the columns?

Properties of Ionic Compounds Na+ Cl- Na+ Cl-

Properties of Ionic Compounds You notice in the second picture that positives and negative line up rather than alternate. Since we know positives repel each other and negatives repel each other the second picture will split down the middle because of the positive-positive and negative-negative repulsion.

Properties of Ionic Compounds In the solid state ionic compounds are nonconductors. However, in a liquid state or dissolved in water they are good conductors. An ionic compound dissolved in water is called an electrolyte. It’s the electrolytes in water that make it a good conductor of electricity. If you have pure water it does not conduct electricity.

Properties of Ionic Compounds Energy and the ionic bond Lattice energy is the energy required to separate one mole of the ions of an ionic compound. Lattice energy is a reflection of strength of the forces holding ions place. The more negative the lattice energy the stronger the attraction.

Homework P.220 #12-18 P.236 #53,67-73