Ionic bonding

Define ‘ionic bonding’

• Electrostatic attraction between positive ions & negative ions

Cations -?

Positive ions

Anions-?

Negative ions

Give 2 examples of cations

1. Metal ions e.g Na+

2. Ammonium ions e.g NH4+

Give 2 examples of anions

• Non-metal ions e.g Cl-

• Polyatomic ions e.g NO3-

Describe the structure of ionic compounds + give 1 example

• Giant ionic lattice

• Example: Sodium chloride

→ Each Na+ is surrounded by 6 Cl- ions

→ Each Cl- is surrounded by 6 Na+ ions

What does solubility require? (2 Main processes)

1. Ionic lattice must be broken down

2. Water molecules must attract & surround ions

Describe melting & boiling points of ionic compounds

• High temp needed to provide large amount of energy to overcome strong electrostatic forces of attraction between positive & negative ions in giant ionic lattices

• The higher the ionic charge, the stronger the electrostatic forces between positive & negative ions & therefore the higher the melting 7 boiling point

Describe solubility of ionic compounds

• Many ionic compounds dissolve in polar solvents e.g water

• Polar water molecules break down the lattice & surround each ion in solution

• In a compound made of ions with large charges, ionic attraction may be too strong for water to break down giant lattice structure therefore ionic compound may not be very soluble

• The solubility of an ionic compound depends on relative strengths of attraction within giant ionic lattice & attraction between ions + water molecules

Describe electric conductivity of ionic compounds

• In the solid state, ions are in fixed positions in giant ionic lattice & no mobile charge carriers therefore an ionic compound is a non-conductor of electricity in solid state

• In the liquid state or in solution, the solid ionic lattice breakdown sown & ions are now free to move as mobile charge carriers therefore an ionic compound is a conductor of electricity in liquid & aqueous states

What state are ionic compounds at - at room temperature?

• Almost all ionic compounds are solids at room temp

• At room temp, there is insufficient energy to overcome strong electrostatic forces of attraction between positive & negative ions