Problem 63 - Chemistry

Question

Name the compounds in parts a-d and write the formulas for the compounds in parts e-h. a. \(\mathrm{NaBr}\) b. \(\mathrm{Rb}_{2} \mathrm{O}\) c. \(\mathrm{CaS}\) d. \(\mathrm{AlI}_{3}\) e. strontium fluoride f. aluminum selenide g. potassium nitride h. magnesium phosphide

Step-by-Step Solution

Answer

a. Sodium bromide b. Rubidium oxide c. Calcium sulfide d. Aluminum iodide e. \(\mathrm{SrF}_{2}\) f. \(\mathrm{Al}_{2}\mathrm{Se}_{3}\) g. \(\mathrm{K}_{3}\mathrm{N}\) h. \(\mathrm{Mg}_{3}\mathrm{P}_{2}\)

Step 1: Naming the Given Compounds

To name the given compounds, we'll identify the cation (positive ion) and the anion (negative ion) for each compound and use the rules for naming ionic compounds. a. \(\mathrm{NaBr}\): Cation: \(\mathrm{Na}\) - Sodium Anion: \(\mathrm{Br}\) - Bromide Compound name: Sodium bromide b. \(\mathrm{Rb}_{2} \mathrm{O}\): Cation: \(\mathrm{Rb}\) - Rubidium Anion: \(\mathrm{O}\) - Oxide Compound name: Rubidium oxide c. \(\mathrm{CaS}\): Cation: \(\mathrm{Ca}\) - Calcium Anion: \(\mathrm{S}\) - Sulfide Compound name: Calcium sulfide d. \(\mathrm{AlI}_{3}\): Cation: \(\mathrm{Al}\) - Aluminum Anion: \(\mathrm{I}\) - Iodide Compound name: Aluminum iodide

Step 2: Writing the Formulas for the Given Compound Names

To write the formulas for the given compound names, we'll determine the chemical symbols and charges for each element and combine them to find the correct molecular formula. e. strontium fluoride: Cation: Sr (Charge: +2) Anion: F (Charge: -1) Compound formula: \(\mathrm{SrF}_{2}\) f. aluminum selenide: Cation: Al (Charge: +3) Anion: Se (Charge: -2) Compound formula: \(\mathrm{Al}_{2}\mathrm{Se}_{3}\) g. potassium nitride: Cation: K (Charge: +1) Anion: N (Charge: -3) Compound formula: \(\mathrm{K}_{3}\mathrm{N}\) h. magnesium phosphide: Cation: Mg (Charge: +2) Anion: P (Charge: -3) Compound formula: \(\mathrm{Mg}_{3}\mathrm{P}_{2}\)

Key Concepts

Chemical Nomenclature

Understanding chemical nomenclature is crucial for anyone studying chemistry. It is the systematic method for naming chemical compounds and ensures clear communication among scientists. The rules for naming ionic compounds involve identifying the cation (positive ion) and the anion (negative ion) first and foremost. The cation is named first and is typically the metal in the compound; it keeps its elemental name, such as Sodium in NaBr. The anion follows and is usually a nonmetal with its ending changed to '-ide', like Bromide in NaBr.

Additionally, in cases where the metal can form ions of different charges, a Roman numeral is used after the metal's name to indicate its charge. For example, Iron(II) chloride indicates that iron has a charge of +2. When naming compounds, no prefixes are used to denote quantity; instead, the charges of the ions dictate the ratios in the formula. Understanding these conventions is essential for correct communication in chemistry.

Ionic Compound Formulas

The formula of an ionic compound represents the ratio of cations to anions which balances out the overall charge. Unlike molecules, ionic compounds are composed of a lattice of ions and do not have a single molecular unit. For example, \( \mathrm{Mg}_3\mathrm{P}_2 \) shows that magnesium phosphide has three magnesium ions for every two phosphide ions to balance the +2 and -3 charges, giving a neutral compound. Here's a simplified way to determine the formula:

• Write down the symbols of the cation and anion.
• Determine the charge of each ion.
• Find the lowest common multiple of the ion charges to balance the compound's charge.
• Write the formula with subscripts indicating the number of each ion required to balance the charges.

Remember that the overall charge of an ionic compound must be zero, and the ratio of the ions is expressed in the smallest whole numbers.

Cation and Anion Identification

Identifying the cation and anion in an ionic compound is a foundational skill in chemistry. In most ionic compounds, the cation is a metal and the anion is a nonmetal. The cation is identified by its location in the periodic table and is usually the first element in the formula, such as Al in Aluminum iodide, \( \mathrm{AlI}_3 \). The cation typically has a positive charge resulting from the loss of electrons.

The anion is the second part of the compound and tends to gain electrons, giving it a negative charge. Anions often stem from nonmetals and are identified by the '-ide' ending, as with Oxide from oxygen in Rubidium oxide, \( \mathrm{Rb}_2\mathrm{O} \). Recognizing these ions in compounds is key to understanding ionic bonds and how elements combine to form compounds.

Chemical Formula Writing

Writing the chemical formula of an ionic compound requires a clear understanding of the charges of the cation and anion. It's a balancing act to ensure neutrality. The general steps are simple:

• Determine the valency or charge of each ion.
• Use the crossover method, where the charge on the cation becomes the subscript for the anion, and vice versa, to balance the charges.
• If necessary, reduce the subscripts to the smallest whole number ratio that balances the charge.

For example, in aluminum selenide, aluminum has a +3 charge and selenium a -2 charge. Transposing these charges, we get \( \mathrm{Al}_2\mathrm{Se}_3 \), with each subscript indicating the number of ions needed to achieve a neutral compound. Accurately writing chemical formulas is crucial for predicting reactions and understanding material properties.