Final answer:
To balance charges of polyatomic ions, use parentheses around the ion's formula and a subscript for the quantity when needed to make the total charges equal zero. In chemical equations, treat polyatomic ions as units, and in net ionic equations, balance by both mass and charge.
Step-by-step explanation:
To balance the charges of polyatomic ions in ionic compounds, the process involves ensuring that the combined charges of the cations (positive ions) and the anions (negative ions) equal zero. When you have more than one of the same polyatomic ion, you must use parentheses to enclose the ion's formula and place a numerical subscript outside the parentheses to indicate the quantity. For instance, in the compound calcium nitrate, the charge is balanced by the presence of two nitrate ions (NO3-) for every one calcium ion (Ca2+), resulting in the formula Ca(NO3)2. This showcases that the positive and negative charges balance out.
When balancing chemical equations that involve polyatomic ions, treat these ions as single units if they appear on both sides of the equation. For example, if you have the phosphate ion (PO43-) present in both reactants and products, balance PO4 as a whole rather than balancing individual phosphorus and oxygen atoms. Additionally, if fractional coefficients are used during balancing, it's important to multiply both sides of the equation by the appropriate factor to achieve whole number coefficients.
Net ionic equations require balancing by both mass and charge. To correctly balance the equation, it might involve adding electrons to one side to achieve the same overall charge on each side of the equation. Remember to always count the number of atoms of each kind to ensure the equation is balanced.