Question

In the following pairs of binary compounds determine which one is a molecular substance and which one is an ionic substance. Use the appropriate naming convention (for ionic or molecular substances) to assign a name to each compound: (a) \(\mathrm{SiF}_{4}\) and \(\mathrm{LaF}_{3}\), (b) \(\mathrm{FeCl}_{2}\) and \(\mathrm{ReCl}_{6}\) (c) \(\mathrm{PbCl}_{4}\) and \(\mathrm{RbCl}\).

Short answer

The identified compounds with their names are: (a) silicon tetrafluoride (molecular) and lanthanum fluoride (ionic), (b) iron(II) chloride (ionic) and rhenium hexachloride (molecular), (c) lead(IV) chloride (ionic) and rubidium chloride (ionic).

Step-by-step solution

Identify Metals and Nonmetals

First, we'll identify the metals and nonmetals in each pair of compounds: (a) \(\mathrm{SiF}_{4}\) and \(\mathrm{LaF}_{3}\) Silicon (Si) is a metalloid and Fluorine (F) is a nonmetal. Lanthanum (La) is a metal and Fluorine (F) is a nonmetal. (b) \(\mathrm{FeCl}_{2}\) and \(\mathrm{ReCl}_{6}\) Iron (Fe) is a metal, and Chlorine (Cl) is a nonmetal. Rhenium (Re) is a metal, and Chlorine (Cl) is a nonmetal. (c) \(\mathrm{PbCl}_{4}\) and \(\mathrm{RbCl}\) Lead (Pb) is a metal, and Chlorine (Cl) is a nonmetal. Rubidium (Rb) is a metal, and Chlorine (Cl) is a nonmetal.

Determine Molecular and Ionic Compounds

Now, we'll determine whether each compound is molecular or ionic based on the types of elements involved. (a) \(\mathrm{SiF}_{4}\) and \(\mathrm{LaF}_{3}\) \(\mathrm{SiF}_{4}\) is a molecular compound (metalloid and nonmetal). \(\mathrm{LaF}_{3}\) is an ionic compound (metal and nonmetal). (b) \(\mathrm{FeCl}_{2}\) and \(\mathrm{ReCl}_{6}\) \(\mathrm{FeCl}_{2}\) is an ionic compound (metal and nonmetal). \(\mathrm{ReCl}_{6}\) is a molecular compound (metal and nonmetal, but Re is an exception due to its covalent bonding nature). (c) \(\mathrm{PbCl}_{4}\) and \(\mathrm{RbCl}\) \(\mathrm{PbCl}_{4}\) is an ionic compound (metal and nonmetal). \(\mathrm{RbCl}\) is an ionic compound (metal and nonmetal).

Apply Naming Conventions

Finally, we will apply the naming conventions for each compound: (a) \(\mathrm{SiF}_{4}\) and \(\mathrm{LaF}_{3}\) \(\mathrm{SiF}_{4}\) (molecular) - silicon tetrafluoride \(\mathrm{LaF}_{3}\) (ionic) - lanthanum fluoride (b) \(\mathrm{FeCl}_{2}\) and \(\mathrm{ReCl}_{6}\) \(\mathrm{FeCl}_{2}\) (ionic) - iron(II) chloride \(\mathrm{ReCl}_{6}\) (molecular) - rhenium hexachloride (c) \(\mathrm{PbCl}_{4}\) and \(\mathrm{RbCl}\) \(\mathrm{PbCl}_{4}\) (ionic) - lead(IV) chloride \(\mathrm{RbCl}\) (ionic) - rubidium chloride

Key concepts

Molecular Compounds

Molecular compounds are formed when two or more nonmetals share electrons through covalent bonds. This specific type of bond is what distinguishes molecular compounds from ionic ones. In these compounds, the atoms are bound together, forming molecules. Since they share electrons rather than transferring them, the resulting bonds are typically weaker than in ionic compounds.

For example, consider \(\mathrm{SiF}_{4}\): silicon is a metalloid and fluorine is a nonmetal. This pairing leads to a covalent molecule, silicon tetrafluoride, because they share electrons rather than transfer them.

Understanding molecular compounds involves recognizing the sharing nature of covalent bonds and the fact that they tend to exist as distinct molecules.

Ionic Compounds

Ionic compounds are characterized by the transfer of electrons from one atom to another, resulting in the formation of ions. This usually involves a metal and a nonmetal, where the metal loses electrons to become a positively charged cation, and the nonmetal gains these electrons to become a negatively charged anion.

These ions attract each other and form a lattice structure. This strong electrostatic attraction is what gives ionic compounds their characteristic properties, like high melting and boiling points.

• For example, \(\mathrm{LaF}_{3}\) is formed when lanthanum, a metal, transfers electrons to fluorine, a nonmetal, resulting in lanthanum fluoride.
• Similarly, \(\mathrm{RbCl}\) forms rubidium chloride when rubidium gives up its electron to chlorine.

Ionic compounds are often quite different in behavior and properties compared to molecular compounds.

Naming Conventions

Naming conventions for chemical compounds are essential for clear and consistent communication in chemistry.

For molecular compounds, the convention typically uses prefixes to indicate the number of each type of atom present in the compound. Common prefixes include "mono-" for one, "di-" for two, "tri-" for three, and "tetra-" for four. For example, \(\mathrm{SiF}_{4}\) is named silicon tetrafluoride, indicating that there are four fluorine atoms.

When it comes to ionic compounds, the naming conventions involve stating the cation first followed by the anion, with no prefixes needed. If the metal has multiple oxidation states, Roman numerals in parentheses follow the cation to indicate its specific charge. \(\mathrm{FeCl}_{2}\) becomes iron(II) chloride, showing that iron has a +2 charge.

Thus, understanding these naming conventions helps ensure proper identification and differentiation of various compounds.