Think of some properties of salt
  • Forms crystals
  • Brittle
  • Hard
  • Solid
  • High melting and boiling point
  • Forms an electrolyte (conducts 
   electricity in water)
       Ionic Compounds
  • NaCl or table salt is an ionic 
   compound.
  • Ionic compounds form from ionic 
   bonds – bonds formed by 
   electrostatic attraction of positive 
   and negative ions
  • Positive ions are called cations
  • Negative ions are called anions
  • Another frequently used description 
   for ionic bonds is that they form 
   when electrons are transferred
         Ionic Compounds
  • Form between metals and nonmetals
  • Or between metals and polyatomic 
    ions (or ammonium and nonmetals).  
    –A polyatomic ion is a covalently bonded 
     compound that has lost or gained 
     electron(s). 
    The polyatomic ion acts as a unit – one 
     thing.  Never change any part of a 
     polyatomic ion.  If you change any 
     subscripts you change the entire ion.  
       Determining ionic compound formulas
     1. Write the element symbols involved in bonding
                 K     O
     2. Next, write the oxidation numbers above the symbols
         + 1      - 2
        K      O 
     3. Now, move the numbers (only the numbers) across to 
        the other symbol’s lower right corner – they become the 
        subscripts
                      + 1         - 2
                    K      O 
        KO
          2
     Compound formulas with polyatomic ions
               + 2      - 3
            Ca   PO4  
                + 2     - 3
             Ca   PO4  
            Ca (PO )
                3      4 2
   You must use parentheses around 
     polyatomic ions if there is more than 
     one of them