This a long process... first you write down the equation,in this case: 2NaCl (aq) + Mg(OH)2 (s) ———> MgCl2 (aq) + 2NaOH (aq) . next you break them up into ions : (only break up the aqueous solutions) (2Na+) + (2Cl-) + Mg(OH)2 {leave it together} ———> (Mg2+) + (2Cl-) + (2Na+) + (2OH-). then look at both sides of equation and cancel the ions that appear twice . In this case: Cl and Na. now the remaining is your final net atomic equation: Mg(OH)2———-> Mg2 + 2OH.