On the basis of the expected charges of the monatomic ions, give the chemical formula of cach of the following compounds: (a) chromium(III) oxide; (b) manganese(II) chloride; (c) lithium nitride.

Understanding oxidation states is paramount when it comes to writing chemical formulas. Simply put, the oxidation state, often called oxidation number, is an indicator of the degree of oxidation of an atom in a chemical compound. It is represented by integers, which can be positive, negative, or zero.

For instance, in the compound chromium(III) oxide, the oxidation state of chromium is indicated by the Roman numeral III, which means that each chromium atom has a +3 charge. Similarly, manganese(II) chloride has manganese with an oxidation state of +2. Knowing these states helps us balance the charges between the positive metal ions and the negative non-metal ions to achieve a neutral compound. A mismatch of these charges would result in an unstable, and therefore, chemically impossible species.

Positive oxidation states often occur with metals, as they tend to lose electrons in chemical reactions, whereas non-metals tend to gain electrons, resulting in negative oxidation states. For example, the oxide ion, with a -2 oxidation state, gains electrons, making it an anion, whereas the chromium(III) ion loses electrons, making it a cation. The two must balance out in a compound for neutrality.

Ionic compounds are formed by the electrostatic attraction between positively charged ions (cations) and negatively charged ions (anions). This attraction results in a stable crystal lattice structure that is characteristic of ionic compounds.

In the steps of solving the textbook exercise, we saw how balancing the total positive and negative charges in a chemical formula is essential to arriving at the correct formulation for an ionic compound. Using the examples given:

• For chromium(III) oxide (Cr_2O_3), two Cr ions with a +3 charge pair with three O ions with a -2 charge.
• For manganese(II) chloride (MnCl_2), one Mn ion with a +2 charge pairs with two Cl ions with a -1 charge.
• For lithium nitride (Li_3N), three Li ions with a +1 charge pair with one N ion with a -3 charge.

It's crucial to remember that the overall charge of an ionic compound must be zero. This balance is what governs the ratios of ions in the chemical formula and dictates the compound's stability.

Chemical nomenclature is a systematic method for naming chemicals so that their names convey descriptive information about their composition. In our exercise, we dealt with the naming of ionic compounds, which involves stating the cation first and the anion second.

The cation retains the same name as the element, like lithium or chromium, and when there are multiple possible oxidation states for an element, a Roman numeral in parentheses, like (II) or (III), specifies the cation’s oxidation state. On the other hand, the anion's name is derived from the element's name, but with an ending change to 'ide', as seen with oxide (O) and nitride (N).

When writing chemical formulae, the cation's symbol is written first followed by the anion's symbol. The subscripts in the chemical formula indicate the number of each ion required to balance the charge. The recommendable approach is to balance the charges without assuming the number of each ion initially, and then adjust to the smallest whole number ratio that balances the charge. This ensures that students don't memorize fixed ratios, but rather understand the reasoning behind the formula's composition.