Write the formulas of (a) potassium hydroxide; (b) barium sulfate; (c) silver chlonide; (d) cupric chloride.

Understanding the valence of ions is crucial when writing chemical formulas, as it correlates with an ion's ability to combine with other ions. The valence, or oxidation state, is a measure of the ion's capacity to accept or donate electrons during chemical reactions. For instance, potassium (K) has a valence of +1, which means it can donate one electron to achieve a stable electronic configuration.

In contrast, the hydroxide ion (OH), carries a valence of -1, indicating it can accept one electron. When these ions (K+ and OH-) come together to form potassium hydroxide (KOH), they do so in a one-to-one ratio to neutralize each other's charges. Students usually find it helpful to visualize the process as a balancing act, where the goal is to attain electrical neutrality in the resulting compound.

Polyatomic ions, such as sulfate (SO₄^2-), cannot be overlooked when writing chemical formulas, as they are composed of two or more atoms covalently bonded that act as a single charged entity. To correctly write the formula for compounds containing polyatomic ions, it's essential to know the ion's formula, charge, and how it interacts with other ions.

Barium sulfate (BaSO₄) is an excellent example, where sulfate is the polyatomic ion with a -2 charge balancing the +2 charge of barium (Ba). Students can benefit from tables or charts of common polyatomic ions to help memorize their formulas and respective charges.

Chemical nomenclature is the standardized system for naming chemical substances. It involves rules that ensure each compound has a unique name, reflecting its composition and structure. When writing the formula for an ionic compound like silver chloride (AgCl), the cation (silver) comes first, followed by the anion (chloride).

The use of prefixes, suffixes, and Roman numerals, as seen in 'cupric chloride' (CuCl₂), corresponds with the charge of the metal ion. 'Cupric' indicates a copper ion with a +2 charge. This is integral in understanding the naming system, particularly for transition metals that can have multiple valences. The application of these rules leads to enhanced comprehension and correct notation of compounds.

Ionic compounds are formed by the electrostatic attraction between positively charged cations and negatively charged anions. Writing formulas for such compounds involves considering the balance of charges, ensuring total neutralization within the compound. The combination of copper(II) ions (Cu²⁺) with chloride ions (Cl^-), to give cupric chloride (CuCl₂), showcases that two chloride ions are needed to balance one copper(II) ion.

When dealing with ionic compounds, it's imperative to not only identify the ions involved but also to understand how to combine them in the proper ratios. Knowledge of valences and the ability to calculate ionic charges plays a significant role in mastering this concept.