Question

Identify each of the following as molecular or ionic, and give its name: (a) \(\mathrm{CrCl}_{2}\) (e) \(\mathrm{KIO}_{3}\) (h) \(\mathrm{AgCN}\) (b) \(\mathrm{S}_{2} \mathrm{Cl}_{2}\) (f) \(\mathrm{P}_{4} \mathrm{O}_{6}\) (i) \(\mathrm{ZnBr}_{2}\) (c) \(\mathrm{SO}_{3}\) (g) \(\mathrm{CaSO}_{3}\) (j) \(\mathrm{H}_{2} \mathrm{Se}\) (d) \(\mathrm{NH}_{4} \mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}_{2}\)

Short answer

(a) Chromium(II) Chloride - Ionic, (e) Potassium Iodate - Ionic, (h) Silver Cyanide - Ionic, (b) Disulfur Dichloride - Molecular, (f) Tetraphosphorus Hexoxide - Molecular, (i) Zinc Bromide - Ionic, (c) Sulfur Trioxide - Molecular, (g) Calcium Sulfite - Ionic, (j) Dihydrogen Selenide - Molecular, (d) Ammonium Acetate - Ionic.

Step-by-step solution

Identify Molecular or Ionic

To determine whether a compound is molecular or ionic, first look at the types of elements it contains. If it is composed of nonmetals only, it is molecular. If it contains a metal and a nonmetal, or a metal and a polyatomic ion, it is ionic.

Name the Compound

For ionic compounds, name the metal (cation) first and the nonmetal (anion) second with an -ide ending if it is a single element. For molecular compounds, use the appropriate prefixes (mono-, di-, tri-, etc.) to denote the number of atoms and name the elements in the order they appear, altering the suffix of the last element to -ide.

Determine and Name Each Compound

Apply Steps 1 and 2 to each compound: (a) CrCl2 is ionic, named Chromium(II) Chloride; (e) KIO3 is ionic, named Potassium Iodate; (h) AgCN is ionic, named Silver Cyanide; (b) S2Cl2 is molecular, named Disulfur Dichloride; (f) P4O6 is molecular, named Tetraphosphorus Hexoxide; (i) ZnBr2 is ionic, named Zinc Bromide; (c) SO3 is molecular, named Sulfur Trioxide; (g) CaSO3 is ionic, named Calcium Sulfite; (j) H2Se is molecular, named Dihydrogen Selenide; (d) NH4C2H3O2 is ionic, named Ammonium Acetate.

Key concepts

Molecular Compounds

Understanding molecular compounds is quite straightforward when you break it down into the basics. These compounds are formed from nonmetals only, meaning they do not contain any metals. The atoms within these compounds are held together by covalent bonds, which occur when atoms share electrons. A perfect example to illustrate this is water (H₂O), where oxygen and hydrogen, both nonmetals, share electrons.

Key Characteristics of Molecular Compounds

Usually, molecular compounds have a low melting and boiling point, and they can be gases, liquids, or solids at room temperature. Their varied states depend on the strength of the covalent bonds between the atoms. For instance, O₂ (oxygen) is a gas, whereas S₈ (sulfur) is a solid. Furthermore, when naming these compounds, prefixes are often used to indicate the number of atoms present. For example, CO₂ is carbon dioxide, where 'di' signifies two oxygen atoms.

In the textbook exercise provided, compounds like S₂Cl₂ (disulfur dichloride) and PH₄O₆ (tetraphosphorus hexoxide) are typical representatives of molecular compounds. They're composed solely of nonmetals and named with prefixes to reflect the number of each type of atom.

Ionic Compounds

When we shift our focus to ionic compounds, we are dealing with the bonds formed between metals and nonmetals, or between metals and polyatomic ions. Ionic bonds are the glue that holds these compounds together and occur when electrons are transferred from one atom to another, forming charged ions. Metals, which tend to lose electrons, become positively charged cations, while nonmetals, which gain electrons, end up as negatively charged anions.

Properties and Naming Ionic Compounds

These compounds are typically solid at room temperature and have high melting and boiling points due to the strong ionic bonds. Salts, such as table salt (NaCl), are common examples of ionic compounds. When naming ionic compounds, the metal (cation) is named first followed by the nonmetal (anion) with an '-ide' suffix if it is a single element. For example, Na₂O is named sodium oxide, not sodium monoxide, as the prefix 'mono-' is not used for the first element.

The exercise's CrCl₂ (chromium(II) chloride) and ZnBr₂ (zinc bromide) highlight the naming method for ionic compounds, with a Roman numeral indicating the charge on the metal if it can hold more than one charge.

Chemical Nomenclature

Chemical nomenclature is the system used for naming chemical compounds. It enables scientists and students to communicate clearly and efficiently about chemical formulas. Consistent rules ensure that each compound has a unique name, avoiding confusion in scientific discussions and literature.

Understanding the System

The International Union of Pure and Applied Chemistry (IUPAC) provides the standard rules for naming compounds. There are different naming conventions for different types of compounds, including binary ionic, molecular (covalent), acids, and organometallic compounds, among others. In binary ionic compounds (like NaCl), the name is straightforward: sodium chloride. However, for compounds with elements that can have more than one charge like iron (Fe), the charge is specified using Roman numerals, such as iron(II) chloride (FeCl₂).

In molecular compounds, the prefixes mono-, di-, tri-, etc., are used to denote the count of each atom involved (such as dinitrogen tetroxide, N₂O₄). Acid nomenclature involves the use of 'hydro-' when the acid is composed of hydrogen and one other element, and '-ic' or '-ous' depending on the presence of oxygen and the number of oxygens relative to hydrogens.

The textbook exercises showcase these rules in action. Compounds such as ammonium acetate (NH₄C₂H₃O₂), sulfur trioxide (SO₃), and potassium iodate (KIO₃) are all named according to the principles of chemical nomenclature, reflecting their molecular makeup and chemical relationships.