1) In order to write formulas of chemical compounds we need the periodic table to find out some oxidation numbers.
Sulfuric acid: H2SO4. This compound has a polyatomic ion called sulfate with a 2- charge. To balance those negative charges we need two H+ ions.
Nitrogen: N2
Oxygen: O2
Ammonia: NH3
Lime: CaCO3. This compound is made up of calcium (Ca2+) and a polyatomic ion called carbonate (CO3 2-). Two positive charges and two negative charges. It is balanced.
Phosphoric acid: H3PO4. This compound has a polyatomic ion called phosphate with a 3- charge. In this compound, we need 3 H+ to balance those negative charges.
Sodium hydroxide: NaOH. Hydroxide compounds have a two-part name. The name of the cation (Na+) and the name of the hydroxide (OH-). One positive charge and one negative charge. It is balanced.
Chlorine: Cl2.
Sodium carbonate: Na2CO3. This compound has a polyatomic ion called carbonate with a 2- charge. We need two positive charges to balance the compound. Sodium is in the first group in the periodic table. That means sodium has just one positive charge, so we need two sodiums.
Nitric acid: HNO3. This compound has a polyatomic ion called nitrate with a 1- charge. To balance that negative charge we need one H+ ion.
