# THREE EASY STEPS… Writing Chemical Formulas. 1. Write the symbol of the cation with its charge. 2. Write the symbol of the anion with its charge. 3. Write.

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THREE EASY STEPS… Writing Chemical Formulas

1. Write the symbol of the cation with its charge. 2. Write the symbol of the anion with its charge. 3. Write in subscript numbers so that the overall charge of the compound is zero. (Use the “criss-cross method”) 4. Reduce to lowest common multiple if necessary.

Example #1—sulfur and aluminum 1. Write the symbol of the cation with its charge. Al +3 2. Write the symbol of the anion with its charge. Al +3 S -2 3. Write in subscript #’s so that the overall charge of the compound is zero. (Use criss- cross method) Al 2 S 3

Example #2—rubidium and bromine 1. Write the symbol of the cation with its charge. Rb +1 2. Write the symbol of the anion with its charge. Rb +1 Br -1 3. Write in subscript #’s so that the overall charge of the compound is zero. (Use criss- cross method) Rb 1 Br 1 RbBr

Example #3—hydroxide ion and calcium 1. Write the symbol of the cation with its charge. Ca +2 2. Write the symbol of the anion with its charge. Ca +2 OH -1 3. Write in subscript #’s so that the overall charge of the compound is zero. (Use criss-cross method) Ca 1 OH 2 Put parentheses around polyatomic ions when you need to indicate more than one. Ca(OH) 2

Example #4—carbonate ion and lead (IV) 1. Write the symbol of the cation with its charge. Pb +4 2. Write the symbol of the anion with its charge. Pb +4 CO 3 -2 3. Write in subscript #’s so that the overall charge of the compound is zero. (Use the criss-cross method). Pb 2 (CO 3 ) 4 Now you finish it off!

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