Question

Write the names of the following ionic compounds. (a) \(\mathrm{Pb}\left(\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}_{2}\right)_{2}\) (b) \(\mathrm{Al}(\mathrm{OH})_{3}\) (c) \(\mathrm{Sr}\left(\mathrm{HCO}_{3}\right)_{2}\) (d) \(\mathrm{Cu}_{3}\left(\mathrm{PO}_{4}\right)_{2}\) (e) \(\mathrm{Rb}_{2} \mathrm{O}\)

Short answer

(a) \(\mathrm{Pb}\left(\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}_{2}\right)_{2}\) (b) \(\mathrm{Al}(\mathrm{OH})_{3}\) (c) \(\mathrm{Sr}\left(\mathrm{HCO}_{3}\right)_{2}\) (d) \(\mathrm{Cu}_{3}\left(\mathrm{PO}_{4}\right)_{2}\) (e) \(\mathrm{Rb}_{2} \mathrm{O}\) Answer: (a) Lead(II) acetate (b) Aluminum hydroxide (c) Strontium bicarbonate (d) Copper(II) phosphate (e) Rubidium oxide

Step-by-step solution

Identify Cations and Anions

In this step, we identify the cations and anions present in each compound. (a) \(\mathrm{Pb}\left(\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}_{2}\right)_{2}\) - Cation: \(\mathrm{Pb}^{2+}\) (Lead ion) and Anion: \(\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}_{2}^-\) (Acetate ion) (b) \(\mathrm{Al}(\mathrm{OH})_{3}\) - Cation: \(\mathrm{Al}^{3+}\) (Aluminum ion) and Anion: \(\mathrm{OH}^-\) (Hydroxide ion) (c) \(\mathrm{Sr}\left(\mathrm{HCO}_{3}\right)_{2}\) - Cation: \(\mathrm{Sr}^{2+}\) (Strontium ion) and Anion: \(\mathrm{HCO}_{3}^-\) (Bicarbonate ion) (d) \(\mathrm{Cu}_{3}\left(\mathrm{PO}_{4}\right)_{2}\) - Cation: \(\mathrm{Cu}^{2+}\) (Copper ion) and Anion: \(\mathrm{PO}_{4}^{3-}\) (Phosphate ion) (e) \(\mathrm{Rb}_{2} \mathrm{O}\) - Cation: \(\mathrm{Rb}^{+}\) (Rubidium ion) and Anion: \(\mathrm{O}^{2-}\) (Oxide ion)

Name the Ionic Compounds

In this step, we will use the identified cations and anions to name each compound. (a) \(\mathrm{Pb}\left(\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}_{2}\right)_{2}\): Lead(II) acetate (b) \(\mathrm{Al}(\mathrm{OH})_{3}\): Aluminum hydroxide (c) \(\mathrm{Sr}\left(\mathrm{HCO}_{3}\right)_{2}\): Strontium bicarbonate (d) \(\mathrm{Cu}_{3}\left(\mathrm{PO}_{4}\right)_{2}\): Copper(II) phosphate (e) \(\mathrm{Rb}_{2} \mathrm{O}\): Rubidium oxide

Key concepts

Chemical Nomenclature

Chemical nomenclature is a set framework of rules to generate the names of chemical compounds. It is vital for scientists to communicate about specific substances unambiguously. When naming ionic compounds, the name of the cation (positive ion) comes first, followed by the name of the anion (negative ion).

For metals that can form more than one type of positive ion, Roman numerals indicate the ion's charge. For example, 'Lead(II)' tells us that lead has a 2+ charge. Nonmetals and polyatomic ions (ions composed of more than one atom) have fixed names, like acetate \(\mathrm{C}_2\mathrm{H}_3\mathrm{O}_2^-\) or hydroxide \(\mathrm{OH}^-\).

In some cases, common names may differ from systematic names. For instance, \(\mathrm{NaCl}\), while scientifically named sodium chloride, is commonly known as table salt. Grasping the systematic approach to chemical nomenclature is essential in understanding chemistry language.

Cation and Anion Identification

To properly name an ionic compound, the first step is identifying the cation and the anion. Cations are positively charged ions, typically metals, which have lost one or more electrons. Anions, on the other hand, are negatively charged ions, typically nonmetals or polyatomic ions, that have gained one or more electrons.

The charge of an ion is determined by the number of electrons lost or gained relative to the neutral atom. Elements in the same group of the periodic table generally form cations or anions with the same charge. For example, alkali metals (Group 1) lose one electron to form a \(1+\) ion, while alkaline earth metals (Group 2) form ions with a \(2+\) charge. On the contrary, halogens (Group 17) tend to gain one electron, thus forming \(1-\) ions. Identifying the charge is crucial because it influences the formula of the compound and the ratio of cations to anions.

Ionic Compound Formulas

Once the cation and anion in an ionic compound are identified, their charges can be used to determine the chemical formula. Ionic compounds are neutral, so the total positive charge must balance the total negative charge. This balancing act is known as the crisscross method: take the absolute value of the charge of one ion and use it as the subscript for the other ion.

For instance, aluminum \(\mathrm{Al}^{3+}\) and hydroxide \(\mathrm{OH}^-\) combine to form aluminum hydroxide with a formula of \(\mathrm{Al}(\mathrm{OH}\)_{3}). Here, the subscript '3' for hydroxide comes from the charge on the aluminum ion. There's no need to include a '1' subscript—the absence of a number implies one.

Writing correct formulas is pivotal in chemistry, as it affects the interpretation of compositions, reactions, and stoichiometry. Students should practice with a variety of ionic compounds to become proficient in writing these formulas.