Final answer:
In an iconic compound, the total positive charge must equal the total negative charge, ensuring that the compound is electrically neutral. This is due to the immutable magnitudes of charge of protons and electrons, which are always equal and opposite.
Step-by-step explanation:
In ionic compounds, the fundamental rule is that the total positive charge of all the positive ions (cations) must equal the total negative charge of all the negative ions (anions). This is because ionic compounds must be electrically neutral overall. This principle is one reason why compounds such as NaCl (sodium chloride) or MgO (magnesium oxide) consist of one-to-one or one-to-two ratios of sodium to chloride ions and magnesium to oxide ions, respectively.
The magnitudes of charge of the proton and the electron are equal, but the charges are opposite: the proton has a positive charge, while the electron has a negative charge. Their charges are well-defined and immutable characteristics of these subatomic particles.
When writing the formula of an ionic compound, we ensure that the ratio of ions results in an electrically neutral compound. This is necessary to satisfy the law of conservation of charge, which states that the total charge in an isolated system remains constant.