For each of the following pairs of ions, write the symbol for the formula of the compound they will form. (a) \(\mathrm{Ca}^{2+}, \mathrm{S}^{2-}\) (b) \(\mathrm{NH}_{4}^{+}, \mathrm{SO}_{4}^{2-}\) (c) \(\mathrm{Al}^{3+}, \mathrm{Br}^{-}\) (d) \(\mathrm{Na}^{+}, \mathrm{HPO}_{4}^{2-}\) (e) \(\mathrm{Mg}^{2+}, \mathrm{PO}_{4}^{3-}\)

When atoms lose or gain electrons, they become ions: positively charged ions are called cations and negatively charged ions are anions. This ionic exchange is driven by the need for atoms to achieve a stable electron configuration, often resembling the closest noble gas configuration. The process of forming compounds from these ions involves the combination of cations and anions to produce a product that is electrically neutral.

Each ion carries a specific charge, indicated by a plus (+) for cations or a minus (-) for anions, alongside a numerical value that shows the relative magnitude of the charge. For example, an ion with a charge of +2 has lost two electrons, while an ion with a charge of -3 has gained three electrons.

Compounds formed from ions are called ionic compounds. They tend to form a crystalline structure and are generally solid at room temperature. These compounds have high melting and boiling points due to the strong electrostatic forces that hold the ions in place within a lattice structure.

To write the correct formula for an ionic compound, one must balance the total positive and negative charges to ensure the compound is electrically neutral. It's like a mathematical puzzle where the sum of the charges must equal zero. The key is to determine the smallest whole-number ratio of ions that leads to neutrality.

If the charges of the ions are equal but opposite, such as +2 and -2, they simply combine in a one-to-one ratio. However, when the charges are different, the quantity of each ion must be adjusted. For example, if a cation has a charge of +3 and an anion has a charge of -2, you would need two cations and three anions to balance the charges and achieve neutrality, resulting in a formula unit with a ratio of 2:3.

Remember, the goal is not to just mix ions together but to create a neutral compound where the total positive charge from the cations exactly cancels out the total negative charge from the anions.

Ionic compounds are substances composed of ions held together by the strong electrostatic forces known as ionic bonds. The ions in these compounds are typically arranged in a regular, repeating pattern that extends in all three spatial dimensions, forming a crystal lattice. This structure contributes to their properties such as high melting points, brittleness, and the ability to conduct electricity when melted or dissolved in water.

Common examples of ionic compounds include table salt (sodium chloride, NaCl) and limestone (calcium carbonate, CaCO3). In writing the chemical formula for such compounds, it is crucial to ensure the correct stoichiometry, which is the ratio of ions that reflects the balance of charge. Ionic compounds are often named by stating the cation first and the anion second, sometimes with a slight change to the anion's name to reflect its status as a part of a compound.