Question

1. write the chemical formula. you do not need to include the charges of the ions.

a. in the case that more than one of a certain polyatomic ion is necessary to balance the charge, the entire formula for the polyatomic ion(s) is enclosed in parentheses and the numerical subscript is placed outside the parentheses. this shows that the subscript applies to the entire polyatomic ion.
example

name	cation	anion	chemical formula

practice exercises
write the chemical formula for each of the following compounds.

1. calcium nitrite
2. potassium carbonate
3. silver citrate
4. aluminum arsenate
5. cadmium sulfite
6. rubidium phosphite
7. strontium hydroxide
8. beryllium sulfate
9. zinc hydrogen sulfate
10. potassium perchlorate

rules for writing formulas for ternary compounds with variable charges

1. identify the cation part of the compound and determine its charge. add the roman numeral as a positive charge to the element symbol.

chemistry 2a - sa 3 writing chemical formulas

Explanation:

Step1: Identify cations and anions

For calcium nitrite, calcium ($Ca^{2 +}$) is the cation and nitrite ($NO_{2}^{-}$) is the anion.

Step2: Balance charges

To balance the +2 charge of calcium, we need 2 nitrite ions. So the formula is $Ca(NO_{2})_{2}$.

Step3: For potassium carbonate

Potassium ($K^{+}$) is the cation and carbonate ($CO_{3}^{2 -}$) is the anion. We need 2 potassium ions to balance the - 2 charge of carbonate, so the formula is $K_{2}CO_{3}$.

Step4: For silver citrate

Silver ($Ag^{+}$) is the cation and citrate ($C_{6}H_{5}O_{7}^{3 -}$) is the anion. We need 3 silver ions to balance the - 3 charge of citrate, so the formula is $Ag_{3}C_{6}H_{5}O_{7}$.

Step5: For aluminum arsenate

Aluminum ($Al^{3+}$) is the cation and arsenate ($AsO_{4}^{3 -}$) is the anion. The charges balance with a 1:1 ratio, so the formula is $AlAsO_{4}$.

Step6: For cadmium sulfite

Cadmium ($Cd^{2+}$) is the cation and sulfite ($SO_{3}^{2 -}$) is the anion. The charges balance with a 1:1 ratio, so the formula is $CdSO_{3}$.

Step7: For rubidium phosphite

Rubidium ($Rb^{+}$) is the cation and phosphite ($PO_{3}^{3 -}$) is the anion. We need 3 rubidium ions to balance the - 3 charge of phosphite, so the formula is $Rb_{3}PO_{3}$.

Step8: For strontium hydroxide

Strontium ($Sr^{2+}$) is the cation and hydroxide ($OH^{-}$) is the anion. We need 2 hydroxide ions to balance the + 2 charge of strontium, so the formula is $Sr(OH)_{2}$.

Step9: For beryllium sulfate

Beryllium ($Be^{2+}$) is the cation and sulfate ($SO_{4}^{2 -}$) is the anion. The charges balance with a 1:1 ratio, so the formula is $BeSO_{4}$.

Step10: For zinc hydrogen sulfate

Zinc ($Zn^{2+}$) is the cation and hydrogen sulfate ($HSO_{4}^{-}$) is the anion. We need 2 hydrogen - sulfate ions to balance the + 2 charge of zinc, so the formula is $Zn(HSO_{4})_{2}$.

Step11: For potassium perchlorate

Potassium ($K^{+}$) is the cation and perchlorate ($ClO_{4}^{-}$) is the anion. The charges balance with a 1:1 ratio, so the formula is $KClO_{4}$.

Answer:

1. $Ca(NO_{2})_{2}$
2. $K_{2}CO_{3}$
3. $Ag_{3}C_{6}H_{5}O_{7}$
4. $AlAsO_{4}$
5. $CdSO_{3}$
6. $Rb_{3}PO_{3}$
7. $Sr(OH)_{2}$
8. $BeSO_{4}$
9. $Zn(HSO_{4})_{2}$
10. $KClO_{4}$