Problem 45 - Chemistry: The Central Science

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 \(\mathrm{RbCl}\).

Step-by-Step Solution

Answer

(a) \(\mathrm{SiF}_{4}\) is a molecular compound named Silicon tetrafluoride, and \(\mathrm{LaF}_{3}\) is an ionic compound named Lanthanum fluoride. (b) \(\mathrm{FeCl}_{2}\) is an ionic compound named Iron(II) chloride, and \(\mathrm{ReCl}_{6}\) is named Rhenium hexachloride. (c) \(\mathrm{PbCl}_{4}\) is an ionic compound named Lead(IV) chloride, and \(\mathrm{RbCl}\) is an ionic compound named Rubidium chloride.

Step 1: Identify the type of compound (ionic or molecular)

First, we need to identify whether the given compounds are ionic or molecular based on the elements involved. (a) \(\mathrm{SiF}_{4}\): Si (Silicon) is a metalloid and F (Fluorine) is a non-metal. Since it is a compound of a metalloid and a non-metal, it is a molecular compound. \(\mathrm{LaF}_{3}\): La (Lanthanum) is a metal and F (Fluorine) is a non-metal. Since it is a compound of a metal and a non-metal, it is an ionic compound. (b) \(\mathrm{FeCl}_{2}\): Fe (Iron) is a metal and Cl (Chlorine) is a non-metal. Since it is a compound of a metal and a non-metal, it is an ionic compound. \(\mathrm{ReCl}_{6}\): Re (Rhenium) is a metal and Cl (Chlorine) is a non-metal. Since it is a compound of a metal and a non-metal, it is an ionic compound. (c) \(\mathrm{PbCl}_{4}\): Pb (Lead) is a metal and Cl (Chlorine) is a non-metal. Since it is a compound of a metal and a non-metal, it is an ionic compound. \(\mathrm{RbCl}\): Rb (Rubidium) is a metal and Cl (Chlorine) is a non-metal. Since it is a compound of a metal and a non-metal, it is an ionic compound. Now that we have identified the type of each compound, we can use the appropriate naming convention for each.

Step 2: Name the compounds using appropriate naming conventions

(a) For molecular compound \(\mathrm{SiF}_{4}\), we can use the following naming convention: element(prefix for the number of atoms) + second element(prefix for the number of atoms). In this case, the name is Silicon tetrafluoride. For ionic compound \(\mathrm{LaF}_{3}\), we can use the following naming convention: cation (metal) + anion (non-metal with -ide suffix). In this case, the name is Lanthanum fluoride. (b) For ionic compound \(\mathrm{FeCl}_{2}\), we can use the naming convention: cation with the roman numeral indicating its charge + anion with -ide suffix. In this case, the name is Iron(II) chloride. For ionic compound \(\mathrm{ReCl}_{6}\), the name is Rhenium hexachloride using molecular compound naming since it's a coordination complex. (c) For ionic compound \(\mathrm{PbCl}_{4}\), we can use the naming convention: cation with the roman numeral indicating its charge + anion with -ide suffix. In this case, the name is Lead(IV) chloride. For ionic compound \(\mathrm{RbCl}\), we can use the following naming convention: cation (metal) + anion (non-metal with -ide suffix). In this case, the name is Rubidium chloride.

Key Concepts

Ionic Compounds

Ionic compounds are formed when metals and non-metals combine. These compounds result from the transfer of electrons, which creates ions. Metals tend to lose electrons and become positively charged ions, while non-metals gain electrons and become negatively charged ions. This electrostatic attraction between the positive and negative ions forms an ionic bond.

Understanding ionic compounds involves recognizing their composition. A metal and a non-metal together usually indicate an ionic compound. For example, LaF e, FeCl e, PbCl, and RbCl are all ionic compounds. In each case, you have a metal (Lanthanum, Iron, Lead, or Rubidium) and a non-metal (Fluorine or Chlorine).

In terms of nomenclature, ionic compounds follow a specific naming convention:

• First, name the cation (metal).
• Then name the anion (non-metal) by changing the ending to '-ide'.
• For metals that can have multiple charges, use Roman numerals to specify the charge.

For instance, FeCl e is named Iron(II) chloride, indicating that iron is in the +2 oxidation state.

Molecular Compounds

Molecular compounds differ from ionic compounds as they consist of non-metals. In these compounds, atoms share electrons through covalent bonds. This happens because non-metals have similar electronegativities, making it energetically favorable for them to share electrons instead of transferring them.

In molecular compounds, like SiF e, the sharing of electrons results in the formation of discrete molecules. Silicon (Si) and Fluorine (F) are both non-metals, which leads to the formation of a molecular compound.

When naming molecular compounds, we apply different rules compared to ionic compounds. The naming involves the use of prefixes to indicate the number of atoms involved. For SiF e, you would name it as Silicon tetrafluoride:

• The first element keeps its name (Silicon).
• For the second element, use a prefix based on the number of atoms (tetra for four), followed by the element name with an '-ide' suffix (fluoride).

Naming Conventions

Naming chemical compounds correctly is crucial for clear communication in science. Different types of compounds have distinct naming conventions to avoid confusion. Whether you are dealing with ionic or molecular compounds, knowing the rules is essential.

Ionic Compounds Naming

The naming begins with the cation (typically a metal), followed by the anion (usually a non-metal). Here are the basic rules:

• Name the metal (cation) first.
• For anions, take the root of the element's name and add '-ide'.
• For metals that can have different charges (like transition metals), use Roman numerals to show the charge (e.g., Iron(II) chloride for FeCl e).

Molecular Compounds Naming

Molecular naming uses prefixes to denote the number of atoms. This makes it clear how many of each type of atom is in the compound.

• Use prefixes like mono-, di-, tri-, tetra-, penta-, etc.
• The first element’s full name is used.
• The second element uses a prefix and ends in '-ide'.

For example, CO e is carbon dioxide, not carbon(IV) oxide, highlighting its molecular structure. Knowing and applying these rules can significantly help in understanding chemical notation and communication.