Ions and Ionic compounds

What is an ion?

• An ion is an atom (or group of atoms) that has lost or gained electrons.
  
  

• Losing electrons → positive ion (cation)
  
  

• Gaining electrons → negative ion (anion)
  
  

• Opposite charges attract, forming ionic bonds.
  
  

Naming Ions

Metal ions → Keep the element name

• e.g. Magnesium ion (Mg²⁺), Aluminium ion (Al³⁺)
  
  

Non-metal ions → Change the ending to -ide

• e.g. Chloride ion (Cl⁻), Oxide ion (O²⁻)
  
  

Polyatomic Ions

These are ions made up of more than one atom that stay together.
Examples:

These ions are often found in compounds with metals and form salts.

How Ionic Compounds Form

• A metal gives electrons to a non-metal.
  
  

• This forms a cation (metal) and an anion (non-metal).
  
  

• They attract and form an ionic bond.
  
  

• The result is an ionic compound, often called a salt.
  
  

Example:
Sodium (Na) + Chlorine (Cl) → Sodium chloride (NaCl)

Naming Ionic Compounds

Two-element compounds:

• Metal name + non-metal name ending in -ide
  
  

  • Magnesium + chlorine → Magnesium chloride
    
    

  • Lithium + oxygen → Lithium oxide
    
    

  • Aluminium + nitrogen → Aluminium nitride
    
    

With polyatomic ions:

• Metal name + name of the polyatomic ion
  
  

  • Na₂SO₄ → Sodium sulfate
    
    

  • CaCO₃ → Calcium carbonate
    
    

  • Fe(NO₃)₃ → Iron nitrate
    
    

  • AlPO₄ → Aluminium phosphate
    
    

Types of Reactions

1. Precipitation Reactions

• Two solutions mix and form an insoluble solid (precipitate).
  
  

• The solid formed is usually a salt.
  
  

Examples (word equations):

• Silver nitrate + sodium chloride → silver chloride (precipitate) + sodium nitrate
  
  

• Barium chloride + sodium sulfate → barium sulfate (precipitate) + sodium chloride
  
  

• Lead nitrate + potassium iodide → lead iodide (precipitate) + potassium nitrate