7 2 Ionic Bonds and Ionic Compounds Main

7. 2 Ionic Bonds and Ionic Compounds Main Idea: Oppositely charged ions attract each other, forming electrically neutral ionic compounds. Essential Questions: 1. How do ionic bonds form and how are the ions arranged in an ionic compounds? 2. What can you conclude about the strength of ionic bonds based on the physical properties of ionic compounds? 3. Is ionic bond formation exothermic or endothermic?

Formation of an Ionic Bond �An ionic bond is the electrostatic force that holds oppositely charged particles together. �An ionic compound is a compound that contains ionic bonds. �Binary ionic compounds are formed between a metal and nonmetal. �Ternary ionic compounds are formed between a metal (or ammonium) and a polyatomic ion.

�The total positive charge of the metal (or ammonium) ion must equal the negative charge of the nonmetal or polyatomic ion. �The overall charge MUST EQUAL ZERO!

�An ionic compound that is made of a metal and oxygen is called an OXIDE. �Examples: � Mg. O � Na 2 O �An ionic compound that is made of a metal and any other negative ion is called a SALT. �Examples: � Na. Cl � Mg. Cl 2

Properties of Ionic Compounds �Positive and negative ions exist together in a fixed ratio. �Packed together into a regular repeating pattern that balances the forces of attraction and repulsion. �Positive ions are surrounded by negative ions and negative ions are surrounded by positive ones. �This forms a crystal lattice structure.

�Physical properties: �High melting point �High boiling point �Hard, rigid, brittle �Conduct electricity in the liquid state or when dissolved in water (electrolyte)

Energy and the Ionic Bond �The formation of ionic compounds is always EXOTHERMIC. �Lattice energy – the energy required to break apart 1 mole of an ionic compound �Greater lattice energy = stronger force of attraction �Smaller ions = stronger attraction = greater lattice energy �Larger + or – charge = greater lattice energy