1. Identify the ions present in the compound: Determine the cation (positive ion) and the polyatomic ion (negative ion) present in the compound.
2. Write the symbols of the ions: Use the chemical symbols for the cation and polyatomic ion. For example, Na+ for sodium ion, Cl- for chloride ion, SO4^2- for sulfate ion, etc.
3. Determine the charges of the ions: Check the charges of the individual ions. Polyatomic ions usually have a net negative charge, while cations have a net positive charge.
4. Balance the charges: Since compounds must be electrically neutral, the total positive charge from the cations must balance the total negative charge from the anions. Adjust the number of each ion (coefficients) as needed to achieve this balance.
5. Write the chemical formula: Combine the symbols and coefficients of the ions to write the chemical formula of the compound. Enclose the polyatomic ion in parentheses if it contains more than one atom.
Here are a few examples:
Sodium chloride (NaCl): Sodium ion (Na+) has a +1 charge, and the chloride ion (Cl-) has a -1 charge. One Na+ ion and one Cl- ion combine to form a neutral compound with the chemical formula NaCl.
Calcium sulfate (CaSO4): Calcium ion (Ca2+) has a +2 charge, and the sulfate ion (SO4^2-) has a -2 charge. One Ca2+ ion and one SO4^2- ion combine to form a neutral compound with the chemical formula CaSO4.
Potassium nitrate (KNO3): Potassium ion (K+) has a +1 charge, and the nitrate ion (NO3-) has a -1 charge. One K+ ion and one NO3- ion combine to form a neutral compound with the chemical formula KNO3.
