Problem 46 - Chemistry: The Central Science in SI Units, Global Edition

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) \(\mathrm{TiCl}_{4}\) and \(\mathrm{CaF}_{2}\), (b) \(\mathrm{ClF}_{3}\) and \(\mathrm{VF}_{3}\), (c) \(\mathrm{SbCl}_{5}\) and \(\mathrm{AlF}_{3}\).

Step-by-Step Solution

Answer

(a) \(\mathrm{TiCl}_{4}\): ionic, titanium tetrachloride; \(\mathrm{CaF}_{2}\): ionic, calcium fluoride. (b) \(\mathrm{ClF}_{3}\): molecular, chlorine trifluoride; \(\mathrm{VF}_{3}\): ionic, vanadium(III) fluoride. (c) \(\mathrm{SbCl}_{5}\): molecular, antimony pentachloride; \(\mathrm{AlF}_{3}\): ionic, aluminum fluoride.

Step 1: (a) Identify the type of bond in \(\mathrm{TiCl}_{4}\) and \(\mathrm{CaF}_{2}\)

To identify the bond type, we need to look at the elements involved in the compounds: - \(\mathrm{TiCl}_{4}\) consists of \(\mathrm{Ti}\) (a metal, titanium) and \(\mathrm{Cl}\) (a non-metal, chlorine). - \(\mathrm{CaF}_{2}\) consists of \(\mathrm{Ca}\) (a metal, calcium) and \(\mathrm{F}\) (a non-metal, fluorine). Since both compounds consist of a metal and a non-metal, they both exhibit ionic bonding.

Step 2: (a) Name \(\mathrm{TiCl}_{4}\) and \(\mathrm{CaF}_{2}\) using ionic conventions

Ionic compounds are named by stating the cation (metal) first, followed by the anion (non-metal) with an "-ide" ending. - \(\mathrm{TiCl}_{4}\): titanium tetrachloride - \(\mathrm{CaF}_{2}\): calcium fluoride

Step 3: (b) Identify the type of bond in \(\mathrm{ClF}_{3}\) and \(\mathrm{VF}_{3}\)

Again, let's look at the elements in each compound: - \(\mathrm{ClF}_{3}\) consists of \(\mathrm{Cl}\) (a non-metal, chlorine) and \(\mathrm{F}\) (a non-metal, fluorine). - \(\mathrm{VF}_{3}\) consists of \(\mathrm{V}\) (a metal, vanadium) and \(\mathrm{F}\) (a non-metal, fluorine). \(\mathrm{ClF}_{3}\) consists of only non-metals, indicating a covalent bond; \(\mathrm{VF}_{3}\) has both a metal and a non-metal, indicating an ionic bond.

Step 4: (b) Name \(\mathrm{ClF}_{3}\) and \(\mathrm{VF}_{3}\) using relevant conventions

- \(\mathrm{ClF}_{3}\) (molecular): Use the standard covalent naming with prefixes: chlorine trifluoride. - \(\mathrm{VF}_{3}\) (ionic): vanadium(III) fluoride. (The (III) indicates a +3 charge on the vanadium ion).

Step 5: (c) Identify the type of bond in \(\mathrm{SbCl}_{5}\) and \(\mathrm{AlF}_{3}\)

Once more, look at the elements in each compound: - \(\mathrm{SbCl}_{5}\) consists of \(\mathrm{Sb}\) (a metalloid, antimony) and \(\mathrm{Cl}\) (a non-metal, chlorine). - \(\mathrm{AlF}_{3}\) consists of \(\mathrm{Al}\) (a metal, aluminum) and \(\mathrm{F}\) (a non-metal, fluorine). \(\mathrm{SbCl}_{5}\) has a metalloid and a non-metal, indicating a molecular bond; \(\mathrm{AlF}_{3}\) has a metal and a non-metal, indicating an ionic bond.

Step 6: (c) Name \(\mathrm{SbCl}_{5}\) and \(\mathrm{AlF}_{3}\) using relevant conventions

- \(\mathrm{SbCl}_{5}\) (molecular): antimony pentachloride. - \(\mathrm{AlF}_{3}\) (ionic): aluminum fluoride.

Key Concepts

Ionic Compounds

Ionic compounds are essential in chemistry due to their distinct properties and structure. They form when a metal and a non-metal combine. In this combination, the metal loses electrons to become a positively charged ion (cation), and the non-metal gains those electrons to become a negatively charged ion (anion). This process is called ionic bonding.
This transfer of electrons results in the attraction between oppositely charged ions, forming a stable compound.

• Examples include:
  • Calcium fluoride ( \(\mathrm{CaF}_2\) )
  • Vanadium(III) fluoride ( \(\mathrm{VF}_3\) )
  • Aluminum fluoride ( \(\mathrm{AlF}_3\) )

Ionic compounds typically have high melting and boiling points due to the strong electrostatic forces between ions. They are often hard and brittle and conduct electricity in molten form or when dissolved in water, as the ions are free to move. Understanding these properties helps in identifying and working with ionic substances. Let’s explore how these characteristics stand in contrast to molecular compounds next.

Molecular Compounds

Unlike ionic compounds, molecular compounds consist of non-metal elements bonded together through the sharing of electrons. This sharing process is known as covalent bonding. In a covalent bond, atoms tend to share electrons to achieve a full outer electron shell, resembling the electron configuration of noble gases for added stability. This results in the formation of molecules with distinct and unique structures.

• Examples include:
  • Chlorine trifluoride ( \(\mathrm{ClF}_3\) )
  • Antimony pentachloride ( \(\mathrm{SbCl}_5\) )

Molecular compounds usually have lower melting and boiling points compared to ionic compounds because the intermolecular forces holding them together, such as van der Waals forces, hydrogen bonds, or dipole-dipole interactions, are typically weaker than ionic bonds. While they may not conduct electricity, their diverse range of structures and reactivity make them critically important in the field of chemistry. Understanding the differences between molecular and ionic compounds helps in predicting their behaviors and uses.

Naming Conventions in Chemistry

Understanding how to correctly name chemical compounds is crucial for clear communication in science. The naming conventions differ significantly between ionic and molecular compounds, reflecting their different natures.
For ionic compounds, the name starts with the cation (metal) followed by the anion (non-metal), with the non-metal ending typically changed to "-ide." If the metal can form ions with different charges, a Roman numeral indicating the charge is included in parentheses.

• For example, in \(\mathrm{VF}_3\), the metal vanadium can have multiple oxidation states, hence it is named vanadium(III) fluoride.
• In \(\mathrm{CaF}_2\), calcium forms a consistent charge, so it is simply named calcium fluoride.

For molecular compounds, prefixes are used to indicate the number of each type of atom in the compound. The molecule's name ends in "-ide" as well.

• For example, \(\mathrm{ClF}_3\) is named chlorine trifluoride, indicating three fluorine atoms.
• Similarly, \(\mathrm{SbCl}_5\) is called antimony pentachloride to show five chlorine atoms in the compound.

Mastery of these naming conventions not only aids in understanding chemical formulas but also provides insight into the composition and structure of compounds.