The equations written up to this point have been molecular equations. All substances have been written using their full chemical formulas as if they were molecules.
Because we now know that strong electrolytes dissociate in water to their component ions, it is more accurate to write an ionic equation in which all of the ionic species are shown.
Note that the NO3 and K+ ions are unchanged on the reactant side and the product side in this equation. Ions that are unchanged are termed spectator ions. The essential part of this chemical reactionthe formation of the lead iodide precipitatecan be shown by eliminating the spectator ions and writing the net ionic equation.
To write a net ionic equation:
- Write a balanced molecular equation.
- Rewrite the equation showing the ions that form in solution when each soluble electrolyte dissociates into its component ions. Only dissolved strong electrolytes are written in ionic form.
- Identify and cancel the spectator ions that occur unchanged on both sides of the equation.