Ionic Bonding & Ionic Compounds

Objectives Explain how ionic compounds are formed Explain the electrical charge of an ionic compound Describe three properties of ionic compounds

Important Vocabulary Ionic compounds Ionic bonds Chemical formula Formula unit Coordination number

Formation of Ionic Compounds Compounds composed of cations and anions are called ionic compounds They usually are the combination of a metal cation with a non-metal anion For example: sodium chloride Although they are composed of ions, ionic compounds are electrically neutral The total positive charge of the cations equals the total negative charge of the anions

Ionic Bonds Opposite charges attract This attraction causes cations and anions to bind together forming an ionic bond An ionic bond is a chemical bond formed between two ions of opposite charges

Formation of an Ionic Bond

Formula Units Chemists represent the composition of substances by writing chemical formulas A chemical formulas shows the kinds and numbers of atoms in the smallest representative unit of a substance A formula unit is the lowest whole- number ratio of ions in an ionic compound

Formula Units Example NaCl is 1 sodium ion & 1 chloride ion The whole-number ratio is 1:1 MgCl 2 is 1 magnesium ion & 2 chloride ions The whole-number ratio is 1:2 Why?

Practice Problems Use electron dot structures to predict the formulas of the ionic compounds formed from the following elements 1. Potassium and oxygen 2. Magnesium and nitrogen 3. Sodium and bromine 4. Aluminum and oxygen

Properties of Ionic Compounds Most are crystalline solids at room temperature The component ions within these crystals are arranged in repeating 3-D patterns The coordination number of an ion is the number of ions of opposite charge that surround the ion in a crystal They usually have high melting points and boiling points They also can conduct electricity when dissolved in water or melted

Ionic Compound Crystals

Coordination Number In sodium chloride, (NaCl) Na + ion has a coordination number of 6 because each one is surrounded by 6 Cl - ions In titanium (IV) oxide, (TiO 2 ) the coordination number for O 2- ion is 3 because it is surrounded by 3 Ti 4+ ions

Conduction of Electricity Why can dissolved or melted ionic compounds conduct electricity?