Determine the compounds needed in the reaction. To create salt, sodium (Na) and chlorine gas (Cl2) is needed. The chemical composition of salt is NaCl. The unbalanced chemical reaction is: Na + Cl2 -> NaCl.
Use a periodic table to determine which compound will be the reducer and which is the oxidizer. Compounds on the left side of the periodic table will be much more likely to donate electrons while compounds to the right will gain electrons. In the salt redox reaction, sodium (Na) oxidizes and chlorine (Cl2) reduces.
Write out the half reactions. Using the periodic table, it can be determined that sodium (Na) can donate one electron (e-) per atom. Therefore the oxidation half reaction is: Na - 1e- -> Na1+.
With the periodic table it is possible to determine that each Cl atom needs to gain 1 electron. Therefore the reduction half reaction is: Cl2 + 2e- -> 2(Cl1-).
Combine the 2 half reactions. Write all the equations out to keep everything straight--this also make its easy to spot any mistakes. The reaction should read: (Na1+ - 1e-) + (Cl2 +2e-) -> 2NaCl.
Balance the new redox equation. To give chlorine (Cl2) the necessary amount of electrons (e-) there needs to be two (Na1+ - 1e-). This newly balanced equations is: 2(Na1+ - 1e-) + Cl2 + 2e- -> 2NaCl. A simplified version becomes: 2Na + Cl2 -> 2NaCl.
Balancing the equation is the most important step. Both sides must be properly balanced. Because Chlorine (Cl) does not naturally occur, you use Cl2 instead. For each chlorine (Cl2) molecule, two salt (NaCl) molecules form.