Question

Name each ionic compound. In each of these compounds, the metal forms only one type of ion. (a) LiI (b) \(\mathrm{MgS}\) (c) \(\mathrm{BaF}_{2}\) (d) \(\mathrm{NaF}\)

Short answer

The names of the compounds are (a) lithium iodide, (b) magnesium sulfide, (c) barium fluoride, and (d) sodium fluoride.

Step-by-step solution

Understanding the concept of naming simple ionic compounds

To name an ionic compound, first name the cation (which is typically a metal) and then name the anion (nonmetal). For the cation, use the element name. For the anion, use the root of the element name and add the suffix '-ide'.

Naming compound (a) LiI

In compound a, 'Li' stands for lithium and 'I' stands for iodine. After applying the naming rule, the cation lithium remains unchanged, and the anion iodine becomes iodide. Thus, the compound name is lithium iodide.

Naming compound (b) \(\mathrm{MgS}\)

In compound b, 'Mg' represents magnesium and 'S' stands for sulfur. By applying the naming rule, the cation magnesium remains the same, and the anion sulfur changes to sulfide. Therefore, the name of this compound is magnesium sulfide.

Naming compound (c) \(\mathrm{BaF}_{2}\)

Compound c has 'Ba' denoting barium and 'F' for fluorine. When the rule is applied, the cation barium keeps its name, while the anion fluorine changes to fluoride. Since there are two fluoride ions for each barium ion, the stoichiometry is taken into account to give the correct formula but does not affect the name. Hence, the compound is named barium fluoride.

Naming compound (d) \(\mathrm{NaF}\)

For compound d, 'Na' is sodium, and 'F' is fluorine. Following the naming rule, sodium remains unchanged, and fluorine becomes fluoride. The compound is therefore called sodium fluoride.

Key concepts

Chemical Nomenclature

Understanding the process of naming chemical substances is crucial in the study of chemistry. Chemical nomenclature provides a systematic way for scientists to communicate formulae and compounds clearly. In ionic compounds, which are made up of cations (positively charged ions) and anions (negatively charged ions), the naming convention is pretty straightforward. The name starts with the cation followed by the anion.

In naming cations, if a metal can form ions with different charges, a roman numeral in parentheses indicates its charge, like iron(III) for Fe³⁺. However, for metals that form only one type of ion, like sodium (Na), no numeral is used. The anion is named by taking the root of the element’s name and adding the suffix ‘-ide’, as seen with chloride (Cl^-) or sulfide (S^2-).

For example, NaCl is named sodium chloride, while MgO is known as magnesium oxide. This naming system allows chemists to infer the composition of a compound from its name, and vice versa.

Cation and Anion Identification

Identification of cations and anions in ionic compounds is a foundational skill in chemistry. In general, cations are usually metal ions and anions are non-metal ions. A helpful way to remember this is that cations are ‘paws-itive’ and tend to come first, similar to their positive position in the periodic table.

When looking at a chemical formula such as LiI or \(\mathrm{NaF}\), the first element (Li and Na, respectively) is the cation, while the second element (I and F, respectively) is the anion. In more complex molecules, such as \(\mathrm{BaF}_2\), the same rule applies - barium (Ba) is the cation and fluorine (F) is the anion. Identifying these ions is a key step in correctly naming the compounds.

Monatomic Ions

Monatomic ions are ions consisting of a single atom with a positive or negative charge, resulting from the loss or gain of electrons. Metals typically form positive monatomic ions (cations), while non-metals form negative monatomic ions (anions).

For example, in sodium chloride (NaCl), sodium (Na⁺) is a monatomic cation, and chloride (Cl^-) is a monatomic anion. The charge on the ion can often be predicted based on the group number in the periodic table. Elements in group 1, like lithium (Li), tend to form +1 cations; whereas, elements in group 17, like fluorine (F), typically form -1 anions.

Stoichiometry

Stoichiometry refers to the quantitative relationship between the reactants and products in a chemical reaction. In the context of naming ionic compounds, stoichiometry can dictate the proportions of cations to anions in the chemical formula. For instance, the ionic compound \(\mathrm{BaF}_{2}\) contains one barium ion (Ba²⁺) and two fluoride ions (F^-).

The subscripts in these formulas provide information on stoichiometry, like the '2' indicating that there are two fluoride ions for every one barium ion. Although stoichiometry impacts the formula of the compound, it does not alter the basic naming procedure. For monatomic ions, stoichiometry ensures charge balance, confirming that the total positive and negative charges in the compound are equal.