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

MgCl2 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

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, (TiO2) the coordination number for O2- ion is 3 because it is surrounded by 3 Ti4+ ions

Conduction of Electricity

Why can dissolved or melted ionic compounds conduct electricity?